CN118202323A - Multi-frequency touch sensing - Google Patents

Abstract

The input device includes a transmitter electrode disposed in a sensing region of the input device, a receiver electrode in the sensing region, and a processing system. The processing system includes a demodulator, and the processing system is configured to simultaneously drive at least a subset of the transmitter electrodes using a plurality of transmitter signals having unique frequencies. The processing system is further configured to receive the resulting signals on the receiver electrodes and demodulate the resulting signals using a plurality of demodulators to generate a plurality of sensing signals. Each of the demodulators operates at a different frequency in the unique frequencies.

Description

Multi-frequency touch sensing

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under Article 8 of the Patent Cooperation Treaty to U.S. patent application serial number 17/518,307 filed on November 3, 2021 and U.S. patent application serial number 17/564,159 filed on December 28, 2021.

Technical Field

The described embodiments relate generally to electronic devices and, more particularly, to touch sensors.

Background technique

Input devices including touch sensor devices (e.g., touch pads or touch sensor devices) are widely used in various electronic systems. A touch sensor device typically includes a sensing area, typically defined by a surface, in which the touch sensor device determines the presence, position, and/or motion of one or more input objects. A touch sensor device can be used to provide an interface for an electronic system. For example, a touch sensor device is typically used as an input device for a larger computing system, such as an opaque touch pad integrated into or external to a notebook or desktop computer. Touch sensor devices exist in different sizes. The number of sensor electrodes in a touch sensor device may depend on the size of the touch sensor device. The number of sensor electrodes in a larger touch sensor device may pose challenges, especially when a higher temporal resolution of touch sensing is desired.

Summary of the invention

Generally, in one aspect, one or more embodiments relate to an input device comprising: a plurality of transmitter electrodes disposed in a sensing region of the input device; receiver electrodes in the sensing region; and a processing system comprising a plurality of demodulators, the processing system being configured to: simultaneously drive at least a subset of the plurality of transmitter electrodes using a plurality of transmitter signals having unique frequencies; receive resulting signals at the receiver electrodes; and demodulate the resulting signals using the plurality of demodulators to generate a plurality of sensing signals, wherein each of the plurality of demodulators operates at a different one of the unique frequencies.

Generally, in one aspect, one or more embodiments relate to a processing system for an input device, the processing system comprising a plurality of demodulators and configured to: simultaneously drive at least a subset of a plurality of transmitter electrodes using a plurality of transmitter signals having unique frequencies, wherein the plurality of transmitter electrodes are disposed in a sensing region of the input device; receive resulting signals at receiver electrodes in the sensing region; and demodulate the resulting signals using the plurality of demodulators to generate a plurality of sensing signals, wherein each of the plurality of demodulators operates at a different one of the unique frequencies.

Generally, in one aspect, one or more embodiments relate to a method for operating an input device, the method comprising: simultaneously driving at least a subset of a plurality of transmitter electrodes using a plurality of transmitter signals having unique frequencies; receiving resulting signals at receiver electrodes, wherein the plurality of transmitter electrodes and the receiver electrodes are disposed in a sensing region of the input device; demodulating the resulting signals using a plurality of demodulators to generate a plurality of sensing signals, wherein each of the plurality of demodulators operates at a different frequency among the unique frequencies; and performing touch sensing using the resulting signals.

Other aspects of the embodiments will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an input device according to one or more embodiments.

FIG. 2 illustrates a sensing configuration according to one or more embodiments.

FIG. 3 illustrates a processing configuration according to one or more embodiments.

FIG. 4 shows a flow chart describing a method for multi-frequency zone touch sensing according to one or more embodiments.

FIG. 5 illustrates sample data in accordance with one or more embodiments.

FIG. 6A illustrates a sensing configuration according to one or more embodiments.

FIG. 6B illustrates a sensing configuration according to one or more embodiments.

FIG. 7 illustrates a processing configuration according to one or more embodiments.

FIG. 8 illustrates an example of inter-band interference analysis according to one or more embodiments.

9 shows a flow chart describing a method for inter-band harmonic interference mitigation for multi-frequency zone parallel scanning according to one or more embodiments.

FIG. 10 shows a flow chart describing a method for multi-frequency zone touch sensing according to one or more embodiments.

Detailed ways

The following detailed description is exemplary in nature and is not intended to limit the invention or the application and use of the invention. In addition, it is not intended to be bound by any express or implied theory presented in the foregoing technical field, background technology, summary of the invention, description of the drawings or the following detailed description.

Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives of elements (i.e., any nouns in this application). The use of ordinal numbers does not imply or create any particular ordering of elements, other than four consecutive quarter periods, nor does it limit any element to only a single element, unless explicitly disclosed, such as by use of the terms "before," "after," "single," and other such terms. Rather, the use of ordinal numbers is to distinguish elements. As an example, a first element is different from a second element, and the first element may contain more than one element and be after (or before) the second element in the ordering of the elements.

The use of ordinal numbers with respect to four consecutive quarter cycles indicates an ordering within the four consecutive quarter cycles. In particular, the first consecutive quarter cycle is the initial quarter cycle preceding the second consecutive quarter cycle. The second consecutive quarter cycle precedes the third consecutive quarter cycle, which in turn precedes the fourth (i.e., last) consecutive quarter cycle.

Various embodiments provide input devices and methods that promote improved usability and various other benefits. Embodiments of the present disclosure can be used to provide high frame rates for touch sensing even for larger sensing areas. Embodiments of the present disclosure use transmitter signals with different frequencies to simultaneously drive multiple sensing electrodes in a sensing area. The simultaneous drive of multiple sensing electrodes can be performed within a shorter time interval than the sequential drive of the same number of sensing electrodes. Therefore, a greater number of sensing operations can be performed during a fixed time interval. Therefore, touch sensing can be performed for a larger sensing area without an undesirable or unacceptable reduction in the frame rate for sensing. Similarly, when using simultaneous drive of multiple sensing electrodes, the frame rate can be increased for a smaller sensing area. A detailed description is provided subsequently.

Fig. 1 is a block diagram of an exemplary input device (100) according to an embodiment. The input device (100) can be configured to provide input to an electronic system (not shown). As used in this document, the term "electronic system" (or "electronic device") broadly refers to any system capable of electronically processing information. Some non-limiting examples of electronic systems include personal computers, such as desktop computers, laptop computers, netbook computers, tablet computers, web browsers, e-book readers, and personal digital assistants (PDAs). Additional example electronic systems include composite input devices, such as physical keyboards including input devices (100) and separate joysticks or key switches. Other example electronic systems include peripheral devices, such as data input devices (including remote controls and mice) and data output devices (including display screens and printers). Other examples include remote terminals, kiosks, and video game consoles (e.g., video game consoles, portable game devices, etc.). Other examples include communication devices (including cellular phones, such as smart phones) and media devices (including recorders, editors, and players, such as televisions, set-top boxes, music players, digital photo frames, and digital cameras). In addition, the electronic system can be a host or slave of the input device.

In FIG. 1 , the input device (100) is shown as a touch sensor device (e.g., a "touchpad" or "touch sensor device") that is configured to sense input provided by one or more input objects in a sensing region (120). Example input objects include a stylus, an active pen (140), and a finger (142). In addition, which specific input objects are in the sensing region can change during the course of one or more gestures. For example, a first input object can be in the sensing region to perform a first gesture, then the first input object and a second input object can be in the upper surface sensing region, and finally, a third input object can perform a second gesture. To avoid unnecessarily complicating the description, the singular form of input object is used and refers to all of the above variations.

The sensing region (120) encompasses any space above, around, in, and/or near the input device (100) where the input device (100) is capable of detecting user input (e.g., user input provided by one or more input objects). The size, shape, and location of a particular sensing region may vary widely from embodiment to embodiment.

The input device (100) may utilize any combination of sensor components and sensing technologies to detect user input in the sensing region (120). The input device (100) includes one or more sensing elements for detecting user input. The sensing elements may be capacitive.

In some capacitive implementations of the input device (100), a voltage or current is applied to create an electric field. Nearby input objects cause changes in the electric field and produce detectable changes in capacitive coupling, which can be detected as changes in voltage, current, etc.

Some capacitive implementations utilize arrays or other regular or irregular patterns of capacitive sensing elements to create an electric field. In some capacitive implementations, individual sensing elements may be ohmically shorted together to form a larger sensor electrode. Some capacitive implementations utilize a resistive sheet, which may be uniformly resistive.

Some capacitive implementations utilize a "self-capacitance" (or "absolute capacitance") sensing method based on changes in the capacitive coupling between a sensor electrode and an input object. In various embodiments, an input object near a sensor electrode changes the electric field near the sensor electrode, thereby changing the measured capacitive coupling. In one implementation, an absolute capacitance sensing method operates by modulating the sensor electrode relative to a reference voltage (e.g., system ground) and by detecting the capacitive coupling between the sensor electrode and the input object. The reference voltage can be a substantially constant voltage or a varying voltage, and in various embodiments, the reference voltage can be system ground. Measurements obtained using an absolute capacitance sensing method can be referred to as absolute capacitive measurements.

Some capacitive implementations utilize a "mutual capacitance" (or "transcapacitance") sensing method based on changes in capacitive coupling between sensor electrodes. In various embodiments, an input object near the sensor electrodes changes the electric field between the sensor electrodes, thereby changing the measured capacitive coupling. In one implementation, the mutual capacitance sensing method operates by detecting the capacitive coupling between one or more transmitter sensor electrodes (also referred to as "transmitter electrodes" or "transmitters") and one or more receiver sensor electrodes (also referred to as "receiver electrodes" or "receivers"). The transmitter sensor electrodes may be modulated relative to a reference voltage (e.g., system ground) to transmit the transmitter signal. The receiver sensor electrodes may remain substantially constant relative to the reference voltage to facilitate reception of the resulting signal. The reference voltage may be a substantially constant voltage, and in various embodiments, the reference voltage may be system ground.

In some embodiments, both the transmitter sensor electrode and the receiver sensor electrode can be modulated. The transmitter electrode can be modulated relative to the receiver electrode to transmit the transmitter signal and facilitate the reception of the result signal. The result signal may include (one or more) effects corresponding to one or more transmitter signals and/or one or more environmental interference sources (e.g., other electromagnetic signals). (One or more) effects can be a transmitter signal, a change in the transmitter signal caused by one or more input objects and/or environmental interference, or other such effects. The sensor electrode can be a dedicated transmitter or receiver, or can be configured to both transmit and receive. The measurement results obtained using the mutual capacitance sensing method can be referred to as mutual capacitance measurement results.

In FIG. 1 , a processing system (110) is shown as part of an input device (100). The processing system (110) is configured to operate the hardware of the input device (100) to detect input in a sensing region (120). The processing system (110) includes part or all of one or more integrated circuits (ICs) and/or other circuit components. For example, a processing system (110) for a mutual capacitance sensor device may include a transmitter circuit configured to transmit a signal using a transmitter sensor electrode, and/or a receiver circuit configured to receive a signal using a receiver sensor electrode. In addition, a processing system (110) for an absolute capacitance sensor device may include a driver circuit configured to drive an absolute capacitance signal onto the sensor electrodes, and/or a receiver circuit configured to receive a signal using those sensor electrodes. In one or more embodiments, a processing system (110) for a combined mutual capacitance and absolute capacitance sensor device may include any combination of the mutual capacitance and absolute capacitance circuits described above. The processing system (110) may also include a receiver circuit configured to receive a signal emitted by a different source (e.g., an active pen (140)). The signal of the active pen (140) may be received by the receiver sensor electrode, while the transmission signal is not necessarily sent by the transmitter sensor electrode.

In some embodiments, the processing system (110) further includes electronically readable instructions, such as firmware code, software code, and/or the like. In some embodiments, the components that make up the processing system (110) are located together, such as near the sensing element(s) of the input device (100). In other embodiments, the components of the processing system (110) are physically separated, with one or more components being near the sensing element(s) of the input device (100) and one or more components being elsewhere. For example, the input device (100) may be a peripheral device coupled to a computing device, and the processing system (110) may include software configured to run on a central processing unit of the computing device and one or more ICs (possibly with associated firmware) separate from the central processing unit. As another example, the input device (100) may be physically integrated into a mobile device, and the processing system (110) may include circuitry and firmware that is part of a main processor of the mobile device. In some embodiments, the processing system (110) is dedicated to implementing the input device (100). In other embodiments, the processing system (110) also performs other functions, such as operating a display screen (155), driving a tactile actuator, and the like.

The processing system (110) may be implemented as a collection of modules that handle different functions of the processing system (110). Each module may include circuitry, firmware, software, or a combination thereof that is part of the processing system (110). In various embodiments, different combinations of modules may be used. For example, as shown in FIG. 1 , the processing system (110) may include a determination module (150) and a sensor module (160). The determination module (150) may include the following functionality: determining when at least one input object is in a sensing area, signal-to-noise ratio, position information of an input object, a gesture, determining an action to be performed based on a gesture, a combination of gestures, or other information, and/or other operations.

The sensor module (160) may include functionality to drive a sensing element to transmit a transmitter signal and receive a result signal. For example, the sensor module (160) may include a sensing circuit coupled to the sensing element. The sensor module (160) may include, for example, a transmitter module and a receiver module. The transmitter module may include a transmitter circuit coupled to a transmitting portion of the sensing element. The receiver module may include a receiver circuit coupled to a receiving portion of the sensing element and may include functionality to receive the result signal. The receiver module of the sensor module (160) may receive the result signal from the sensor electrodes in the electrode pattern using, for example, a capacitive sensing signal having a sensing frequency generated by the transmitter module. The result signal may include a desired signal (such as active pen data or signal components caused by an input object approaching the electrode pattern) or an undesired signal (such as noise or interference). As will be described in more detail below, the sensor module (160) may perform one or more demodulation operations on the result signal.

Although FIG. 1 shows a determination module (150) and a sensor module (160), alternative or additional modules may exist according to one or more embodiments. Such alternative or additional modules may correspond to modules or submodules that are different from one or more of the modules discussed above. Example alternative or additional modules include a hardware operation module for operating hardware such as sensor electrodes and a display screen (155), a data processing module for processing data such as sensor signals and position information, a reporting module for reporting information, and a recognition module configured to recognize gestures such as mode change gestures, and a mode change module for changing the operating mode. In addition, various modules may be combined in separate integrated circuits. For example, a first module may be at least partially included in a first integrated circuit, and a separate module may be at least partially included in a second integrated circuit. In addition, portions of a single module may span multiple integrated circuits. In some embodiments, the processing system as a whole may perform operations of the various modules.

In some embodiments, the processing system (110) responds to user input (or lack of user input) in the sensing area (120) directly by causing one or more actions. Example actions include changing operating modes, and graphical user interface (GUI) actions such as cursor movement, selection, menu navigation, and other functions. In some embodiments, the processing system (110) provides information about the input (or lack of input) to some portion of the electronic system (e.g., to a central processing system of the electronic system that is separate from the processing system (110), if such a separate central processing system exists). In some embodiments, some portion of the electronic system processes the information received from the processing system (110) to act on the user input, such as to facilitate a full range of actions, including mode change actions and GUI actions.

In some embodiments, the input device (100) includes a touch screen interface, and the sensing area (120) overlaps at least a portion of the working area of the display screen (155). For example, the input device (100) may include a substantially transparent sensor electrode covering the display screen and providing a touch screen interface for an associated electronic system. The display screen may be any type of dynamic display capable of displaying a visual interface to a user, and may include any type of light emitting diode (LED), organic LED (OLED), cathode ray tube (CRT), liquid crystal display (LCD), plasma, electroluminescence (EL), or other display technology. The input device (100) and the display screen (155) may share physical elements. For example, some embodiments may utilize some of the same electrical components for display and sensing. In various embodiments, one or more display electrodes of the display device may be configured for both display updating and input sensing. As another example, the display screen (155) may be operated in part or in whole by the processing system (110).

Although FIG. 1 illustrates a configuration of components, other configurations may be used without departing from the scope of the present disclosure. For example, various components may be combined to create a single component. As another example, functionality performed by a single component may be performed by two or more components. Furthermore, although a configuration for touch sensing is described, other variables such as force may be sensed.

FIG. 2 illustrates a sensing configuration (200) according to one or more embodiments. The sensing configuration (200) is based on an arrangement of sensor electrodes in a sensing region (120). Transmitter (Tx) electrodes (220) and receiver (Rx) electrodes (230) may be disposed in the sensing region (120). In the example of FIG. 2 , the Tx electrodes (220) are elongated rectangular structures arranged in columns, and the Rx electrodes (230) are elongated rectangular structures arranged in rows. In general, any shape of Tx and Rx electrodes may be used.

In one or more embodiments, the Tx electrode (220) and the Rx electrode (230) together implement mutual capacitance or transcapacitive sensing. At the intersection of the Tx (220) and Rx (230) electrodes, a local capacitive coupling is formed between a portion of the Tx electrode (220) and the Rx electrode (230). The area of the local capacitive coupling can be referred to as a "capacitive pixel", or also referred to as a sensing element (225) in this article. The transcapacitance Ct is associated with the sensing element (225). When an input object (not shown) approaches the sensing element (225), the transcapacitance Ct can change by an amount ΔCt. Therefore, the presence or absence of the input object can be detected by monitoring ΔCt. ΔCt can be measured by driving a transmitter signal (222) onto the Tx electrode (220) and receiving a result signal (232) from the Rx electrode (230). The result signal is a function of the transmitter signal and the ΔCt caused by the presence or absence of the input object. ΔCt may be obtained for multiple sensing elements to generate a capacitive image, for example, across the entire sensing region ( 120 ).

In one or more embodiments, multiple Tx electrodes (220) are driven simultaneously. In the example of FIG. 2 , when three Tx electrodes are driven simultaneously with transmitter signals Tx _F1 , Tx _F2 and Tx _F3 (222), the resulting signal (232) on each of the Rx electrodes Rx ₁ . . . Rx _n (230) will be affected by Tx _F1 , Tx _F2 and Tx _F3 . Therefore, each of the resulting signals (232) may carry information about the presence or absence of an input object proximate to the three sensing elements (225).

As described with reference to FIG3 , demodulation may be performed so that a sensing signal (225) is obtained for each of the three sensing elements. The described operation may be performed for each of the resultant signals (232) on the Rx electrodes Rx ₁ ... Rx _n (230). To obtain a complete capacitive image, the operation may then be repeated for another set of three Tx electrodes using the same Tx _F1 , Tx _F2 , and Tx _F3 . The repetition may continue until all Tx electrodes (220) are driven. To drive the Tx electrodes (220), the Tx electrodes may be grouped by frequency regions. Based on the use of three frequencies for simultaneous driving in the example of FIG2 , the sensing configuration (200) includes three frequency regions (242, 244, and 246).

Each of the three frequency zones (242, 244, 246) includes the same or nearly the same number of Tx electrodes. For example, if the sensing configuration (200) includes 60 Tx electrodes, each of the frequency zones (242, 244, 246) can contain 20 Tx electrodes. One Tx electrode from each group can be selected for simultaneous drive. For example, as shown in FIG2, the leftmost Tx electrode in each of the frequency zones (242, 244, 246) is selected for simultaneous drive. Next, the immediately adjacent Tx electrodes in each of the frequency zones (242, 244, 246) can be selected for simultaneous drive. Once all Tx electrodes (220) in all three frequency zones (242, 244, 246) have been driven once, and the corresponding result signals (232) have been received on the Rx electrodes (230), a complete capacitive image can be obtained.

In one or more embodiments, multiple Tx electrodes (220) are driven simultaneously. In the example of FIG. 2 , it is assumed that multiple Tx electrodes in frequency zone 1 (242) are driven simultaneously with multiple Tx electrodes in frequency zone 2 (244) and are driven simultaneously with multiple Tx electrodes in frequency zone 3 (246). The simultaneously driven Tx electrodes in frequency zone 1 (242) may be driven using a transmitter signal having a first frequency, the simultaneously driven Tx electrodes in frequency zone 2 (244) may be driven using a transmitter signal having a second frequency, and the simultaneously driven Tx electrodes in frequency zone 3 (246) may be driven using a transmitter signal having a third frequency. If the frequencies of the transmitter signals are selected to satisfy certain orthogonal principles (discussed below with reference to FIG. 3 ), signal processing may be performed separately for different frequency zones with no interference or with minimal interference. In order to be able to locate a touch at a particular sensing element (225), repeated driving may be performed using bursts of the transmitter signal (222), as described in the following example. In this example, it is assumed that there are 20 Tx electrodes (220) per frequency zone (242, 244, 246), i.e., there are 60 Tx electrodes in total for the three frequency zones. Correspondingly, in this example, in each frequency zone, there are 20 sensing elements (225) per Rx electrode that intersect with the 20 Tx electrodes. In order to be able to evaluate the presence or absence of touch at each of the 20 sensing elements (225), a burst mode of 20 sequential bursts (which allows a unique solution to a system of equations with 20 unknowns) can be used to sequentially and simultaneously drive the Tx electrodes 20 times. Although the frequency of the transmitter signal used in the sensing zone can be the same for the entire burst mode, the phase of the transmitter signal can vary across subsequent bursts and across the driven Tx electrodes within the burst mode. By processing the result signal (232) obtained on a single Rx electrode in response to the 20 bursts on all 20 TX electrodes, ΔCt can be determined for each sensing element. The same operation can be performed simultaneously for all result signals (232) on all Rx electrodes (230). The same operation can also be performed simultaneously in other frequency zones.Thus, in the example with three frequency zones, a total of 60 Tx electrodes can be driven simultaneously, each Tx electrode having a sequence of 20 bursts of the transmitter signal.

In the example of FIG. 2 , assuming no other parameters are adjusted, simultaneous driving of the Tx electrodes (220) can reduce the time required to acquire a complete capacitive image by one-third. To illustrate, assuming a desired frame rate of 240fps for a 17" touch screen having 60 Tx electrodes, the available time to drive the Tx electrodes with a burst of transmitter signals would be limited to 1/(240x60)=70μs, which may result in poor noise immunity. In contrast, when a set of Tx electrodes is driven simultaneously across three frequency zones, the available time to drive the Tx electrodes would be 1/(240x 20)=210μs per burst, which may provide superior noise immunity without reducing the frame rate. This may also be the case when operating smaller touch screens at even higher frame rates (e.g., 480fps or 600fps).

Although FIG. 2 shows a specific sensing configuration, and the example describes a specific touch screen scenario, embodiments of the present disclosure can be used in conjunction with many different configurations. For example, embodiments of the present disclosure can use different types of electrode arrangements, can drive fewer or more Tx electrodes at the same time, can be used for larger or smaller sensing areas, etc. Although FIG. 2 shows a specific order for driving a set of three Tx electrodes (220) at the same time, any order for driving the Tx electrodes can be used without departing from the present disclosure. In addition, although FIG. 2 shows a specific configuration of frequency zones (242, 244, 246), frequency zones can be configured differently. For example, frequency zones do not need to be continuous, equal numbers of Tx electrodes can be randomly assigned to frequency zones, and so on.

FIG3 illustrates a processing configuration (300) according to one or more embodiments. The processing configuration (300) can be used in conjunction with the sensing configuration (200) of FIG2 . Specifically, in the example shown in FIG3 , transmitter signals having three different frequencies are simultaneously transmitted to drive the Tx electrode (220) (e.g., as shown in FIG2 ). FIG3 illustrates the processing of a result signal (332) obtained on one of the Rx electrodes (230). In order to process multiple result signals on multiple Rx electrodes, the processing configuration (300) can be implemented multiple times to operate in parallel. For example, for n Rx electrodes, the components shown in FIG3 can be implemented n times.

The processing configuration (300) includes an analog front end (340) and a digital processing block (360). The analog front end (340) may include a charge integrator (342) and an analog-to-digital converter (ADC) (344). The digital processing block (360) may include operations that implement a set of demodulators (362). In the example shown, the set of digitally implemented demodulators (362) demodulates the result signal (332) obtained by the analog front end (340) to generate a sensing signal (364). The sensing signal (364) can provide a measurement of the transcapacitance at the three sensing elements (225) and can therefore indicate the presence or absence of an input object (not shown). Additional downstream operations may be performed on the sensing signal (364) to perform touch sensing. A detailed description is provided later.

In one or more embodiments, the transmitter signals (322) for simultaneously driving a set of transmitter electrodes (230) have different frequencies. More specifically, each simultaneously driven transmitter electrode is driven by a transmitter signal (322) having a unique frequency. In one or more embodiments, the transmitter signals (322) for simultaneous driving are orthogonal. In one or more embodiments, the transmitter signals (322) for simultaneous driving are selected from an orthogonal frequency division multiplexing (OFDM) spectrum of subcarriers, as shown in FIG3. FIG3 shows an example of an OFDM spectrum with eleven subcarriers. Due to the orthogonality of the subcarriers, any subcarrier can be used. For example, the subcarrier at ω ₀ and the subcarriers immediately to the left and right can be selected to obtain a transmitter signal (322) with three different frequencies. The burst of the transmitter signal (322) can then be used to simultaneously drive the Tx electrodes (220) in the sensing area (120). The first of the three frequencies may be used to drive the Tx electrodes in the frequency 1 zone (242), the second of the three frequencies may be used to drive the Tx electrodes in the frequency 2 zone (244), and the third of the three frequencies may be used to drive the Tx electrodes in the frequency 3 zone (246). Although only one frequency may be used within a frequency zone, the phase of the transmitter signal within the frequency zone may vary between electrodes and/or between subsequent bursts of the transmitter signal. In one embodiment, the phase is changed by 180° to drive the Tx electrodes using the transmitter signal and the inverted transmitter signal. Any other phase change may be used without departing from the present disclosure.

A single result signal Rx _{F1, F2, F3 (332) may be obtained from one Rx electrode (232) for further processing. The result signal Rx F1, F2, F3} (332) may include the effects of the transmitter signal (322) transmitted at all sensing elements (225) associated with the Tx electrode, the Tx electrodes being driven with transmitter signals having three different frequencies and different phases. An example is provided in FIG5 . The result signal Rx _{F1, F2, F3} (332) may further include the effects of the presence or absence of an input object at the sensing element (225).

The charge integrator (342) receives the result signal Rx _{F1, F2, F3} (332) and can integrate the result signal Rx _{F1, F2, F3} (332) during an integration time interval. The ADC (344) receives the result signal Rx _{F1, F2, F3} (332) after integration and performs analog-to-digital conversion. Additional discussion of the ADC is provided below.

The output of the ADC is provided to a set of digitally implemented demodulators (362). In one or more embodiments, the demodulators (362) are configured to generate a sensing signal (364). In one or more embodiments, the demodulators (362) include a demodulator for in-phase (I) demodulation and a quadrature (Q) demodulation specific to each of the unique frequencies of the three transmitter signals (322). In other words, there may be six demodulators (three I demodulators and three Q demodulators) configured to perform three I/Q demodulations, as shown in FIG3. Each of the six demodulators may include a multiplier operation and a windowing operation to generate the I and Q components of the sensing signal. The multiplier may multiply the input of the multiplier (i.e., the integrated, analog-to-digital converted result signal Rx _{F1, F2, F3} (332)) with a demodulated waveform to perform demodulation. The windowing operation may provide low pass filtering, such as a weighted average of the mixer results (obtained from the multiplier operation). The demodulated waveform may be based on the transmitter signal (322).

Specifically, a copy of one of the three transmitter signals (322) may be provided to each of the multipliers to cause demodulation at the frequency of the provided transmitter signal. Thus, the demodulator (362) performs code division multiplexing (CDM) decoding at each of the three frequencies in combination to separate the sensing signals (364) associated with the three sensing elements (225). Even in the presence of possible phase shifts, the demodulated I and Q components of the sensing signals associated with the sensing elements may be combined to obtain an acceptably accurate sensing signal.

In the case of using combined I and Q demodulation, accurate phase alignment between the integrated, analog-to-digital converted result signal Rx _{F1, F2, F3} (332) and the demodulated waveform is not required to perform demodulation. Therefore, the ADC (344) can be relatively slow, for example, three to five times the speed of the transmitter signal frequency. This may result in the introduction of phase offsets, which, however, are mitigated by using combined I and Q demodulation. The use of a slow ADC reduces power consumption and cost, while the additional Q demodulator is associated with negligible additional cost and power consumption because it is digitally implemented. Therefore, the described configuration using digital I/Q demodulation and analog-to-digital conversion prior to demodulation is cost-effective and energy-efficient. Although digital I/Q demodulation is described, analog I/Q demodulation can be performed without departing from the present disclosure, followed by analog-to-digital conversion.

In one embodiment, demodulation is performed using only an I demodulator (no Q demodulator). In order to obtain reasonably accurate phase alignment using only an I demodulator, a faster ADC (344) can be used to reduce possible phase offsets. For example, the ADC can operate at a speed at least 16 times the transmitter signal frequency.

Although FIG3 shows a particular processing configuration, other configurations may be used without departing from the present disclosure. For example, although FIG3 shows three Tx electrodes being driven simultaneously using transmitter signals having three unique frequencies, any number of Tx electrodes may be driven simultaneously. Furthermore, although FIG3 shows a processing configuration for processing a single result signal obtained from three Rx electrodes, the analog and digital processing components as shown may be replicated to process additional result signals.

FIG. 4 shows a flow chart according to one or more embodiments. One or more of the steps in FIG. 4 may be performed by the components discussed above with reference to FIG. 1 , FIG. 2 , and FIG. 3 . Although the various steps in the flow chart are presented and described sequentially, it will be appreciated by a person of ordinary skill that at least some of the blocks may be performed in a different order, may be combined or omitted, and some of the blocks may be performed in parallel. Additional steps may be further performed. Therefore, the scope of the present disclosure should not be considered to be limited to the specific arrangement of the steps shown in FIG. 4 .

FIG. 4 is a flow chart depicting a method ( 400 ) for multi-frequency zone touch sensing according to one or more embodiments.

In step 402, a set of Tx electrodes are driven simultaneously using multiple transmitter signals having unique frequencies. Any number of Tx electrodes may be driven simultaneously. Additional details are provided with reference to FIG. 2 and FIG. 3.

In step 404, a result signal is obtained on the Rx electrode. Step 404 can be performed in parallel with step 402. In addition, step 404 can be performed for multiple Rx electrodes at the same time. The result signal received on the Rx electrode is affected by multiple transmitter signals coupled to the Rx electrode. The coupling occurs where the Rx electrode is spatially adjacent to the Tx electrode (e.g., at the sensing element where the Tx electrode intersects the Rx electrode). The result signal is also affected by the presence or absence of an input object close to the sensing element because capacitive coupling is affected by the presence or absence of the input object.

In step 406, the result signal is demodulated to generate a set of sensing signals. A sensing signal can be obtained for each of one or more Tx electrodes driven by a transmitter signal having a specific frequency. If both I demodulation and Q demodulation are performed, the result I and Q components of the sensing signal can be processed to determine the amplitude and/or phase of the sensing signal. Additional details are provided with reference to Figures 2 and 3. Additional steps can be performed before demodulation. For example, as described above, the result signal can be integrated and/or analog-to-digital converted. A solution for sensing a signal specific to a specific sensing element can be obtained by solving the sensing signal on multiple bursts of the transmitter signal. For example, when 20 bursts are used for a configuration including 20 sensing elements, a unique solution can be obtained. If step 404 is performed for multiple Rx electrodes, step 406 can also be performed multiple times to demodulate each of the result signals associated with the multiple Rx electrodes.

The described steps may be repeated. For example, steps 402-406 may be repeated while driving a different set of Tx electrodes selected from the Tx electrodes in the frequency region, as previously described with reference to FIGS. 2 and 3. After performing steps 402-406 for all Tx electrodes in the sensing region, a capacitive image having sensing signals for a complete set of sensing elements of the capacitive image may be available.

In step 408, touch sensing may be performed using the sense signals. Touch sensing may involve evaluating the sense signals against a previously determined baseline value. If the sense signals deviate from the baseline value by at least a certain amount, the input object may be considered to be present in the vicinity of the sensing element corresponding to the sense signal. Step 408 may be performed for some or all sense signals associated with the sensing elements of the capacitive image.

Steps 402 - 408 may be repeated, for example, periodically to perform touch sensing over time.

FIG5 shows sample data (500) according to one or more embodiments. This example is for three Tx electrodes driven simultaneously using three transmitter signals with three unique frequencies. The three frequencies are 100kHz, 109.9kHz, and 119.8kHz. The three frequencies are selected from the OFDM spectrum (e.g., as shown in FIG3).

The resulting signal at the Rx electrode is shown in the time domain (502). The resulting signal is also shown in the frequency domain (504). The contributions of the three transmitter signals are clearly identifiable, although the resolution of the spectrum (obtained using an FFT applied to a single transmitter signal burst) is insufficient to distinguish the three Tx frequencies. The contribution of the noise signal at 50kHz is further visible.

Embodiments of the present disclosure have various advantages. The use of transmitter signals transmitted simultaneously with different frequencies enables touch sensing to be performed on a larger sensing area using a relatively high frame rate without compromising noise immunity. Specifically, embodiments of the present disclosure allow a large number of Tx electrodes (which may be necessary for a larger touch screen) to be driven at a high frame rate without shortening the burst of the transmitted transmitter signal, because multiple transmitter electrodes can be driven simultaneously at different frequencies. Using the burst length as proposed, a high degree of noise immunity is achieved. In addition, embodiments of the present disclosure allow other bursts to be added (e.g., for noise measurement, absolute capacitance sensing, etc.) without significantly changing the timing. For example, in an example where 20 bursts are required per frame, the time required to complete a frame with an additional burst will increase by 5%. Embodiments of the present disclosure are cost-effective and energy-saving, for example, because a relatively slow ADC can be used, and because many demodulation operations can be performed digitally using a standard DSP. Embodiments of the present disclosure also allow the use of transmitter signals based on waveforms including many harmonics. For example, a trapezoidal waveform may be used, which may have several advantages over using a sinusoidal waveform, such as relatively easy generation of higher voltages using transistor stacks, and the ability to operate using lower transmission powers (since the amplitude of the base waveform is 1.27V for a 1V square wave).

In one or more embodiments, a non-sinusoidal transmitter signal is used to simultaneously drive the sensing electrodes. The use of a non-sinusoidal transmitter signal has various advantages, but may result in the emission of higher harmonics. One or more embodiments mitigate interference that may be generated due to the presence of higher harmonics. A detailed description is provided subsequently.

FIG6A illustrates a sensing configuration (600) according to one or more embodiments. The sensing configuration (600) is based on an arrangement of sensor electrodes in a sensing region (120). Transmitter (Tx) electrodes (620) and receiver (Rx) electrodes (630) may be disposed in the sensing region (120). In the example of FIG6A , the Tx electrodes (620) are elongated rectangular structures arranged in columns, and the Rx electrodes (630) are elongated rectangular structures arranged in rows. In general, any shape of Tx and Rx electrodes may be used.

In one or more embodiments, the Tx electrode (620) and the Rx electrode (630) together implement mutual capacitance or transcapacitive sensing. At the intersection of the Tx (620) and Rx (630) electrodes, a local capacitive coupling is formed between a portion of the Tx electrode (620) and the Rx electrode (630). The area of the local capacitive coupling can be referred to as a "capacitive pixel", or also referred to as a sensing element (625) in this article. The transcapacitance Ct is associated with the sensing element (625). When an input object (not shown) approaches the sensing element (625), the transcapacitance Ct can change by an amount ΔCt. Therefore, the presence or absence of the input object can be detected by monitoring ΔCt. ΔCt can be measured by driving a transmitter signal (622) onto the Tx electrode (620) and receiving a result signal (632) from the Rx electrode (630). The result signal is a function of the transmitter signal and the ΔCt caused by the presence or absence of the input object. ΔCt may be obtained for multiple sensing elements to generate a capacitive image, such as across the entire sensing region ( 120 ).

In one or more embodiments, multiple Tx electrodes (620) are driven simultaneously. In the example of FIG. 6A , when three Tx electrodes are driven simultaneously with transmitter signals Tx _F1 , Tx _F2 , and Tx _F3 (622), the resulting signal (632) on each of the Rx electrodes Rx ₁ . . . Rx _n (630) will be affected by Tx _F1 , Tx _F2 , and Tx _F3 . Therefore, each of the resulting signals (632) may carry information about the presence or absence of an input object proximate to the three sensing elements (625).

As described with reference to FIG. 7 , demodulation may be performed so that a sensing signal (625) is obtained for each of the three sensing elements. The described operation may be performed for each of the resultant signals (632) on the Rx electrodes Rx ₁ ... Rx _n (630). To obtain a complete capacitive image, the operation may then be repeated for another set of three Tx electrodes using the same Tx _F1 , Tx _F2 , and Tx _F3 . The repetition may continue until all Tx electrodes (620) are driven. To drive the Tx electrodes (620), the Tx electrodes may be grouped by frequency regions. Based on the use of three frequencies for simultaneous driving in the example of FIG. 6A , the sensing configuration (600) includes three frequency regions (642, 644, and 646).

Each of the three frequency zones (642, 644, 646) includes the same or nearly the same number of Tx electrodes. For example, if the sensing configuration (600) includes 60 Tx electrodes, each of the frequency zones (642, 644, 646) can contain 20 Tx electrodes. One Tx electrode from each group can be selected for simultaneous drive. For example, as shown in FIG6A, the leftmost Tx electrode in each of the frequency zones (642, 644, 646) is selected for simultaneous drive. Next, the adjacent Tx electrode in each of the frequency zones (642, 644, 646) can be selected for simultaneous drive. Once all Tx electrodes (620) in all three frequency zones (642, 644, 646) have been driven once, and the corresponding result signal (632) has been received on the Rx electrode (630), a complete capacitive image can be obtained.

In one or more embodiments, multiple Tx electrodes (620) are driven simultaneously. In the example of FIG. 6A , it is assumed that multiple Tx electrodes in frequency zone 1 (642) are driven simultaneously with multiple Tx electrodes in frequency zone 2 (644) and are driven simultaneously with multiple Tx electrodes in frequency zone 3 (646). The simultaneously driven Tx electrodes in frequency zone 1 (642) may be driven using a transmitter signal having a first frequency, the simultaneously driven Tx electrodes in frequency zone 2 (644) may be driven using a transmitter signal having a second frequency, and the simultaneously driven Tx electrodes in frequency zone 3 (646) may be driven using a transmitter signal having a third frequency. If the frequencies of the transmitter signals are selected to satisfy certain orthogonal principles (discussed below with reference to FIG. 7 ), signal processing may be performed separately for different frequency zones with no interference or with minimal interference. In order to be able to locate a touch at a particular sensing element (625), repeated driving may be performed using bursts of the transmitter signal (622), as described in the following example. In this example, it is assumed that there are 20 Tx electrodes (620) in each frequency zone (642, 644, 646), that is, there are 60 Tx electrodes in total for the three frequency zones. Correspondingly, in this example, in each frequency zone, there are 20 sensing elements (625) for each Rx electrode that intersect with the 20 Tx electrodes. In order to be able to evaluate the presence or absence of touch at each of the 20 sensing elements (625), a burst mode of 20 sequential bursts (which allows a unique solution to a system of equations with 20 unknowns) can be used to sequentially and simultaneously drive the Tx electrodes 20 times. Although the frequency of the transmitter signal used in the sensing area can be the same for the entire burst mode, the phase of the transmitter signal can vary across subsequent bursts and across the driven Tx electrodes within the burst mode. By processing the result signal (632) obtained on a single Rx electrode in response to the 20 bursts on all 20 TX electrodes, ΔCt can be determined for each sensing element. The same operation can be performed simultaneously for all result signals (632) on all Rx electrodes (630). The same operation can also be performed simultaneously in other frequency zones.Thus, in the example with three frequency zones, a total of 60 Tx electrodes can be driven simultaneously, each Tx electrode having a sequence of 20 bursts of the transmitter signal.

In the example of FIG. 6A , assuming no other parameters are adjusted, simultaneous driving of the Tx electrodes (620) can reduce the time required to acquire a complete capacitive image by one-third. To illustrate, assuming a desired frame rate of 240fps for a 17" touch screen with 60 Tx electrodes, the available time to drive the Tx electrodes with a burst of transmitter signals would be limited to 1/(240x60)=70μs, which may result in poor noise immunity. In contrast, when a set of Tx electrodes is driven simultaneously across three frequency zones, the available time to drive the Tx electrodes would be 1/(240x 20)=210μs per burst, which may provide superior noise immunity without reducing the frame rate. This may also be the case when operating smaller touch screens at even higher frame rates (e.g., 480fps or 600fps).

Figure 6B shows a sensing configuration (650) according to one or more embodiments.The physical configuration of the sensing configuration including the arrangement of Tx electrodes (620) and Rx electrodes (630) may be as described with reference to Figure 6A.

In one or more embodiments, multiple Tx electrodes (620) are driven simultaneously. In the example of FIG. 6B , n Tx electrodes (652) are driven simultaneously using transmitter signals Tx _F1 ... Tx _Fn . The n Tx electrodes may include a subset of all Tx electrodes in the sensing region (120) or all Tx electrodes in the sensing region. Therefore, the result signal (662) on each of the Rx electrodes Rx ₁ ... Rx _n (630) will be affected by Tx _F1 ... Tx _Fn . Therefore, each of the result signals (662) may carry information about the presence or absence of an input object approaching the sensing element (655). In order to ensure that touch positioning can be performed for each of the n sensing elements (655), Tx _F1 ... Tx _Fn (652) may be selected to be orthogonal to each other. The described operations may be performed for each of the result signals (662) on the Rx electrodes Rx ₁ ... Rx _n (630).

As previously described with reference to FIG6A , in the example of FIG6B , the simultaneous driving of the Tx electrodes ( 620 ) can reduce the time required to acquire a complete capacitive image. The degree of reduction can depend on various factors, such as how many Tx electrodes are driven simultaneously, the burst mode used to drive the Tx electrodes, etc.

Although FIG. 6A and FIG. 6B illustrate a specific sensing configuration, and the example describes a specific touch screen scenario, embodiments of the present disclosure may be used in conjunction with many different configurations. For example, embodiments of the present disclosure may use different types of electrode arrangements, may drive fewer or more Tx electrodes simultaneously, may be used for larger or smaller sensing areas, etc.

FIG. 7 shows a processing configuration (700) according to one or more embodiments. The processing configuration (700) can be used in combination with the sensing configuration (600) of FIG. 6A. A modified processing configuration (with an additional demodulator) can be used in combination with the sensing configuration (650) of FIG. 6B. Specifically, in the example shown in FIG. 7, a transmitter signal (722) having three different frequencies is simultaneously transmitted to drive the Tx electrode (620) (e.g., as shown in FIG. 6A). The properties of the transmitter signal (722) are discussed below. FIG. 7 shows the processing of the result signal (732) obtained on one of the Rx electrodes (630). In order to process multiple result signals on multiple Rx electrodes, the processing configuration (700) can be implemented multiple times to operate in parallel. For example, for n Rx electrodes, the components shown in FIG. 7 can be implemented n times.

The processing configuration (700) includes an analog front end (740) and a digital processing block (760). The analog front end (740) may include a charge integrator (742) and an analog-to-digital converter (ADC) (744). The digital processing block (760) may include operations that implement a set of demodulators (762). In the example shown, the set of digitally implemented demodulators (762) demodulates the result signal (732) obtained by the analog front end (740) to generate a sensing signal (764). The sensing signal (764) can provide a measurement of the transcapacitance at the three sensing elements (625) and can therefore indicate the presence or absence of an input object (not shown). Additional downstream operations may be performed on the sensing signal (764) to perform touch sensing. A detailed description is provided later.

Each of the transmitter electrodes driven simultaneously is driven by a non-sinusoidal transmitter signal (722) having a unique frequency (e.g., using a trapezoidal or square waveform having a unique fundamental frequency). In one or more embodiments, the non-sinusoidal transmitter signals (722) used for simultaneous driving are orthogonal. Referring to FIG. 6A , bursts of non-sinusoidal transmitter signals can be used to simultaneously drive the Tx electrodes (620) in the sensing region (120). The first of three frequencies can be used to drive the Tx electrodes in the frequency 1 zone (642), the second of the three frequencies can be used to drive the Tx electrodes in the frequency 2 zone (644), and the third of the three frequencies can be used to drive the Tx electrodes in the frequency 3 zone (646). Although only one frequency can be used within a frequency zone, the phase of the non-sinusoidal transmitter signal within the frequency zone can vary between electrodes and/or between subsequent bursts of the non-sinusoidal transmitter signal. In one embodiment, the phase is changed by 180° to drive the Tx electrodes using the non-sinusoidal transmitter signal and the anti-phase non-sinusoidal transmitter signal. Any other phase change can be used without departing from the present disclosure.

A single result signal Rx _{F1, F2, F3 (732) may be obtained from one Rx electrode (632) for further processing. The result signal Rx F1, F2, F3} (732) may include the effects of the non-sinusoidal transmitter signal (722) transmitted at all sensing elements (625) associated with the Tx electrode, the Tx electrode being driven with the non-sinusoidal transmitter signal having three different fundamental frequencies and different phases. The result signal Rx _{F1, F2, F3} (732) may further include the effects of the presence or absence of an input object at the sensing element (625).

The charge integrator (742) receives the result signal Rx _{F1, F2, F3} (732) and can integrate the result signal Rx _{F1, F2, F3} (732) within an integration time interval. The ADC (744) receives the result signal Rx _{F1, F2, F3} (732) after integration and performs analog-to-digital conversion.

The output of the ADC is provided to a set of digitally implemented demodulators (762). In one or more embodiments, the demodulators (762) are configured to generate a sense signal (764). In one or more embodiments, the demodulators (762) include a demodulator for in-phase (I) demodulation and a quadrature (Q) demodulation specific to each of the unique frequencies of the three non-sinusoidal transmitter signals (722). In other words, there may be six demodulators (three I demodulators and three Q demodulators) configured to perform three I/Q demodulations, as shown in FIG7. Each of the six demodulators may include a multiplier operation and a windowing operation to generate the I and Q components of the sense signal. The multiplier may multiply the input to the multiplier (i.e., the integrated, analog-to-digital converted result signal Rx _{F1, F2, F3} (732)) by the demodulation waveform to perform demodulation. The windowing operation may provide a low pass filtering, such as a weighted average of the mixer results (obtained from the multiplier operation). As discussed further below, the windowing operation may pass the signal at the fundamental frequency of the corresponding non-sinusoidal transmitter signal while strongly attenuating the fundamental frequencies of other (orthogonal) non-sinusoidal transmitter signals. The demodulation waveform may be based on the non-sinusoidal transmitter signal (722). For example, the demodulation waveform may be a sinusoidal waveform at the fundamental frequency of the corresponding non-sinusoidal transmitter signal.

Thus, each demodulator performs demodulation at the fundamental frequency of the corresponding non-sinusoidal transmitter signal. The demodulator (762) performs code division multiplexing (CDM) decoding at each of the three fundamental frequencies in combination to separate the sensing signals (764) associated with the three sensing elements (625). Even in the presence of possible phase shifts, the demodulated I and Q components of the sensing signals associated with the sensing elements can be combined to obtain an acceptably accurate sensing signal.

In the case of using combined I and Q demodulation, precise phase alignment between the integrated, analog-to-digital converted result signal Rx _{F1, F2, F3} (732) and the demodulated waveform is not required to perform demodulation. Therefore, the ADC (744) can be relatively slow, for example, three to five times the speed of the fundamental frequency of the non-sinusoidal transmitter signal frequency. This may result in the introduction of phase offsets, which are however mitigated by using combined I and Q demodulation. The use of a slow ADC reduces power consumption and cost, while the additional Q demodulator is associated with negligible additional cost and power consumption because it is digitally implemented. Therefore, the described configuration using digital I/Q demodulation and analog-to-digital conversion prior to demodulation is cost-effective and energy-efficient. Although digital I/Q demodulation is described, analog I/Q demodulation can be performed without departing from the present disclosure, followed by analog-to-digital conversion.

In one embodiment, demodulation is performed using only an I demodulator (no Q demodulator). In order to obtain reasonably accurate phase alignment using only an I demodulator, a faster ADC (744) may be used to reduce possible phase offsets. For example, the ADC may operate at a speed of at least 16 times the fundamental frequency of the non-sinusoidal transmitter signal frequency.

As previously described, one or more embodiments employ a non-sinusoidal transmitter signal (722). In the example of FIG. 7 , a single non-sinusoidal transmitter signal having a trapezoidal waveform may be used. Any other non-sinusoidal waveform, such as a square wave, may be used without departing from the present disclosure. Non-sinusoidal waveforms may have various advantages over sinusoidal waveforms. For example, it may be relatively easy to synthesize non-sinusoidal waveforms using basic circuit elements. It may further be relatively easy to generate non-sinusoidal waveforms having an amplitude higher than a system voltage. For example, a 9V amplitude may be achieved using a 3V system voltage. In addition, a non-sinusoidal waveform may have a higher signal energy at a fundamental frequency than a sinusoidal waveform having the same nominal amplitude. In FIG. 7 , a trapezoidal waveform used as a non-sinusoidal transmitter signal (722) is shown in the time domain (left) and the frequency domain (right). The trapezoidal waveform has a fundamental frequency of 100kHz and an amplitude of 1V. As the spectrum shows, the amplitude at the fundamental frequency is 1.254V (1.97dB). Therefore, at the fundamental frequency, for the same voltage of the non-sinusoidal transmitter signal, the trapezoidal waveform has higher signal energy than the sine wave, thereby providing various potential advantages, such as the ability to use a lower transmitter signal voltage, obtain a higher signal-to-noise ratio when using the same voltage, etc. However, as shown in FIG7 , non-sinusoidal waveforms such as trapezoidal waveforms also include harmonics that are different from the fundamental frequency. In the case of the trapezoidal waveform shown in FIG7 , there is a 3rd (700kHz) harmonic, a 5th (500kHz) harmonic, etc. In the spectrum shown in FIG7 , the fundamental frequency amplitude of the third harmonic is 10.6dB lower than the fundamental frequency, the fundamental frequency amplitude of the fifth harmonic is 17.4dB lower than the fundamental frequency, etc. The total harmonic distortion of the first 10 harmonics is -9.6dB.

Due to the presence of higher harmonics, in one or more embodiments, aliasing occurs at the ADC (744). The effects of aliasing may be detrimental to the accuracy of the sensed signal (764). The effects are subsequently described based on the following scenario. Assume that the three fundamental frequencies of the non-sinusoidal transmitter signal (722) are 100kHz, 109.9kHz, and 119.8kHz. The fundamental frequencies of the 200μs burst length are spaced 9.9kHz apart, which results in orthogonality (or near orthogonality) when demodulation is performed using a Hanning window (discussed below). Other frequency spacings may be used for other types of windows, other burst lengths, etc. In addition, assume that the ADC sampling frequency Fs of the ADC (744) is set to 500kHz. At Fs=500kHz, the Nyquist frequency is 250kHz. Therefore, aliasing (722) occurs for the higher harmonics of all three non-sinusoidal transmitter signals. As a result of aliasing, in one or more embodiments, the higher harmonics appear as aliasing artifacts at the output of the ADC (744) at lower frequencies.

A combination of shift and fold operations may be used to determine the lower frequency at which the aliasing artifact occurs. If the higher harmonics that are the result of aliasing appear as aliasing artifacts at or near one of the fundamental frequencies of the non-sinusoidal transmitter signal, an erroneous sensing signal may result. In the above example, the 5th harmonic of the non-sinusoidal transmitter signal at 119.8kHz is 5x 119.8kHz = 599kHz. Using shift and fold operations to perform aliasing analysis, the 5th harmonic appears as an aliasing artifact at 99kHz when a 500kHz ADC sampling frequency is used. Because 99kHz is close to the 100kHz fundamental frequency of one of the non-sinusoidal transmitter signals, the sensing signal obtained for the demodulation performed at 100kHz is not accurate.

In one or more embodiments, the ADC sampling frequency Fs is selected to reduce errors caused by higher harmonics that appear as aliasing artifacts near the fundamental frequency. More specifically, Fs is adjusted so that no aliasing artifacts are close to any fundamental frequency. The desired Fs can be selected by systematically changing Fs while monitoring inter-band interference (i.e., the presence of aliasing artifacts near the fundamental frequency). The desired Fs can be the Fs at which the inter-band interference is minimized. A description of inter-band interference is subsequently provided with reference to the example shown in FIG8.

Although FIG7 shows a specific processing configuration, other configurations may be used without departing from the present disclosure. For example, although FIG7 shows the use of non-sinusoidal transmitter signals having three unique fundamental frequencies to simultaneously drive three Tx electrodes, any number of non-sinusoidal transmitter signals may be used to simultaneously drive any number of Tx electrodes. In addition, although FIG7 shows a processing configuration for processing a single result signal obtained from three Rx electrodes, the analog and digital processing components as shown may be replicated to process additional result signals.

FIG8 shows an example of inter-band interference analysis according to one or more embodiments. In this example, Fs is adjusted within a range of 500kHz +/- 10% to identify an Fs with an acceptably low inter-band interference. The frequency range analyzed is limited (in this example, +/- 10%) to reduce the possibility of interference caused by external noise (noise originating from a source different from the input device). External noise can originate from various components, such as power supplies, display devices, etc. External noise can be concentrated at a specific frequency, and an initial Fs (500kHz) can be selected so that it is less likely to be interfered with by external noise. Therefore, the variation of Fs within a limited range reduces the possibility of selecting a frequency where external noise causes significant interference.

As shown in the inter-band interference graph (802) in FIG8 , the inter-band interference is determined as Fs is adjusted in the frequency range from 450kHz to 550kHz. Inter-band interference is an indication of the amount of interference caused by driving one or more Tx electrodes at a first frequency while digitally demodulating at a second frequency (after A/D conversion and possible aliasing). Referring to the example of using 100kHz, 109.9kHz and 119.8kHz for a non-sinusoidal transmitter signal previously introduced, the following inter-band interference may occur due to aliasing:

(i) driven at 100 kHz and demodulated at 109.9 kHz;

(ii) driven at 100 kHz and demodulated at 119.8 kHz;

(iii) driven at 109.9kHz and demodulated at 100kHz;

(iv) driven at 109.9 kHz and demodulated at 119.8 kHz;

(v) driven at 119.8 kHz and demodulated at 100 kHz; and

(vi) Driven at 119.8kHz and demodulated at 109.9kHz.

Inter-band interference for each of these six cases can be obtained across a frequency range. Therefore, a graph (802) can be obtained for each of the six cases. Each graph may include high frequencies at which inter-band interference is unacceptably high, and may also include low or very low frequencies at which inter-band interference is acceptable. As shown in the graph (802), given a particular scenario, for lower Fs, the inter-band interference is particularly high, while for higher Fs, the inter-band interference is low to very low.

The inter-band interference summary (804) summarizes the results for the worst frequency (Fs=449kHz) and the best frequency (Fs=520kHz). When the non-sinusoidal transmitter signal is transmitted at F2 (109.9kHz) and the demodulation is performed at F3 (119.8kHz), the worst case interference is found to be 21.491%. This inter-band interference is clearly visible in the graph (802) (leftmost peak). In contrast, for the best frequency, all interference remains below 0.02%. The almost complete absence of interference can be seen in the graph (802) (magnified frequency range).

An optimization may be performed to select Fs at which interference is acceptable for all six cases. A method for determining Fs is discussed below. Although the example in FIG8 is for three non-sinusoidal transmitter signals, a similar analysis may be performed for any number of non-sinusoidal transmitter signals.

Figures 9 and 10 show flow charts according to one or more embodiments. One or more of the steps in Figures 9 and 10 may be performed by the components discussed above with reference to Figures 1, 6A, 6B, and 7. Although the various steps in these flow charts are presented and described sequentially, it will be appreciated by those of ordinary skill that at least some of the steps may be performed in a different order, may be combined or omitted, and some of the steps may be performed in parallel. Additional steps may be further performed. Therefore, the scope of the present disclosure should not be considered to be limited to the specific arrangement of the steps shown in Figures 9 and 10.

FIG. 9 is a flow chart depicting a method ( 700 ) for inter-band harmonic interference mitigation for multi-frequency zone parallel scanning according to one or more embodiments.

In step 902, a noise measurement is performed. Noise can be measured under realistic operating conditions, for example, in the presence of possible noise sources such as a display, power supply, etc. The noise measurement can be used to distinguish between frequency regions with noise and frequency regions with less noise or no noise. Spectral analysis can be performed to make the distinction.

In step 904, a non-sinusoidal transmitter signal is selected so that the interference of the noise identified in step 902 is avoided or at least reduced. In other words, for the non-sinusoidal transmitter signal, a frequency region in which relatively small noise exists can be selected. For example, assume that noise is detected at 50kHz based on the execution of step 902. In order to avoid the detected noise, the fundamental frequency of the non-sinusoidal transmitter signal can be placed in a region of about 100kHz. The frequency spacing of the fundamental frequency, the burst length, the shape of the non-sinusoidal transmitter signal, etc. can be selected so that certain orthogonality requirements and timing requirements are met, as discussed previously. Step 904 can be performed for any number of non-sinusoidal transmitter signals transmitted simultaneously. Although the flowchart shows the measurement of noise and the selection of non-sinusoidal transmitter signals as separate steps, these steps can be combined. For example, a set of selected non-sinusoidal transmitter signals can be used to perform measurements. If it is found that there is too much noise based on the measurement, a different set of non-sinusoidal transmitter signals can be selected. Switching to a different set of non-sinusoidal transmitter signals can continue until it is identified that the noise is determined to be an acceptable set.

In step 906, a sampling frequency Fs of an analog-to-digital converter (ADC) is selected. In one or more embodiments, Fs is selected so that aliasing artifacts associated with higher harmonics of the non-sinusoidal transmitter signal are located at a frequency different from the fundamental frequency of the non-sinusoidal transmitter signal. In other words, Fs is adjusted to reduce the amplitude of the aliasing artifacts at the fundamental frequency to reduce or eliminate inter-band harmonic interference. Additional details are provided with reference to FIG. 7. The selection of Fs can be performed starting from a default sampling frequency. The optimization can be performed within a limited range around the default sampling frequency. The optimization can be performed to minimize the aliasing artifacts at the fundamental frequency of the non-sinusoidal transmitter signal. Any standard can be used to specify an acceptable aliasing level at the fundamental frequency. For example, 1/1000 of the inter-band harmonic interference can be set as a threshold. Step 906 can be performed for a single set of non-sinusoidal transmitter signals or multiple sets of non-sinusoidal transmitter signals in different frequency ranges. Using multiple sets of non-sinusoidal transmitter signals can enable the input device to operate in different frequency ranges, for example, depending on the noise environment. The operation of step 906 can be performed by measuring the inter-band harmonic interference on an actual input device or by simulation. If simulation is used, the different components of the input device can be approximated by simulation models. For example, the characteristics of the sensing element and the analog front end can be approximated by a first-order (single-pole) simulation model, which has time constants that respectively approximate the characteristics of the actual sensing element and the actual analog front end.

The operations of steps 902-906 may be performed during setup or manufacture of the input device to program one or more sets of frequencies for the non-sinusoidal transmitter signal and the matching sampling frequency Fs into the input device. Alternatively, steps 902-906 may be performed during operation of the input device.

In step 908, touch sensing may be performed. A description is provided below with reference to FIG.

FIG. 10 is a flow chart depicting a method ( 1000 ) for multi-frequency zone touch sensing according to one or more embodiments.

In step 1002, a set of Tx electrodes are driven simultaneously using multiple non-sinusoidal transmitter signals having unique fundamental frequencies. Any number of Tx electrodes may be driven simultaneously. Additional details are provided with reference to FIG. 6A, FIG. 6B and FIG. 7.

In step 1004, a result signal is obtained on the Rx electrode. Step 1004 can be performed in parallel with step 1002. In addition, step 1004 can be performed simultaneously for multiple Rx electrodes. The result signal received on the Rx electrode is affected by multiple non-sinusoidal transmitter signals coupled to the Rx electrode. The coupling occurs where the Rx electrode is in close proximity to the Tx electrode (e.g., at the sensing element where the Tx electrode intersects the Rx electrode). The result signal is also affected by the presence or absence of an input object close to the sensing element because capacitive coupling is affected by the presence or absence of the input object.

In step 1006 , the resulting signal is analog-to-digital converted using an analog-to-digital converter operating at the sampling frequency Fs determined in step 906 .

In step 1008, after analog-to-digital conversion, the result signal is demodulated to generate a set of sensing signals. A sensing signal can be obtained for each of one or more Tx electrodes driven by a non-sinusoidal transmitter signal having a specific frequency. If both I demodulation and Q demodulation are performed, the resulting I and Q components of the sensing signal can be processed to determine the amplitude and/or phase of the sensing signal. Additional details are provided with reference to FIG. 6A, FIG. 6B and FIG. 7. A solution for sensing a signal specific to a specific sensing element can be obtained by solving the sensing signal on multiple bursts of the non-sinusoidal transmitter signal. For example, when 20 bursts are used for a configuration including 20 sensing elements, a unique solution can be obtained. If step 1004 is performed for multiple Rx electrodes, step 1008 can also be performed multiple times to demodulate each of the result signals associated with the multiple Rx electrodes.

The described steps may be repeated. For example, steps 602-606 may be repeated while driving a different set of Tx electrodes selected from the Tx electrodes in the frequency region, as previously described with reference to FIGS. 6A , 6B, and 7 . After performing steps 602-608 for all Tx electrodes in the sensing region, a capacitive image having sensing signals for a complete set of sensing elements of the capacitive image may be available.

In step 1010, touch sensing may be performed using the sense signals. Touch sensing may involve evaluating the sense signals against a previously determined baseline value. If the sense signals deviate from the baseline value by at least a certain amount, the input object may be considered to be present near the sensing element corresponding to the sense signal. Step 1010 may be performed for some or all sense signals associated with the sensing elements of the capacitive image.

Steps 1002 - 1010 may be repeated, for example, periodically to perform touch sensing over time.

Embodiments of the present disclosure have various advantages. The use of transmitter signals transmitted simultaneously with different frequencies enables a large number of Tx electrodes to be driven at a high frame rate (which may be necessary for a larger touch screen) without shortening the burst of the transmitted transmitter signal. Embodiments of the present disclosure use non-sinusoidal waveforms. Non-sinusoidal waveforms have the advantage of being relatively easy to generate, even if the amplitude is higher than the system voltage. In addition, non-sinusoidal waveforms have a higher voltage amplitude at the base frequency than sinusoidal waveforms. The higher signal energy generated at the base frequency provides various advantages, such as the ability to use a lower transmitter signal voltage, obtain a higher signal-to-noise ratio when using the same voltage, etc.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art having benefit of this disclosure will appreciate that other embodiments can be designed which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the present invention should be limited only by the claims appended hereto.

Claims (15)

1. An input device, comprising: transmitter electrodes disposed in a plurality of separate frequency zones in a sensing region of the input device, wherein each of the plurality of separate frequency zones comprises a plurality of transmitter electrodes; receiver electrodes in the sensing region; and A processing system comprising a plurality of demodulators, the processing system being configured to: simultaneously driving at least two of the plurality of transmitter electrodes in each of the plurality of separate frequency zones using a plurality of transmitter signals having unique frequencies; receiving a resulting signal at the receiver electrode; and demodulating the resultant signal using the plurality of demodulators to generate a plurality of sensing signals, wherein each of said plurality of demodulators operates at a different one of said unique frequencies, and Wherein each of the plurality of individual frequency regions is specific to one of the unique frequencies. 2. The input device according to claim 1, Wherein simultaneously driving at least two of the plurality of transmitter electrodes in each of the plurality of separate frequency zones using the plurality of transmitter signals having unique frequencies comprises: At least two of the plurality of transmitter electrodes are simultaneously driven at one of the unique frequencies specific to the frequency zone. 3. The input device according to claim 1, Wherein simultaneously driving at least two of the plurality of transmitter electrodes in each of the plurality of separate frequency zones using the plurality of transmitter signals having unique frequencies comprises: At least two of the plurality of transmitter electrodes are simultaneously driven in a first frequency zone of the plurality of separate frequency zones at a first frequency of the unique frequency, and at least two of the plurality of transmitter electrodes are simultaneously driven in a second frequency zone of the plurality of separate frequency zones at a second frequency of the unique frequency. The input device of claim 1 , wherein the transmitter signals in the plurality of transmitter signals are orthogonal to each other. 5. The input device of claim 1, wherein the plurality of transmitter signals are selected from an Orthogonal Frequency Division Multiplexing (OFDM) spectrum. 6. The input device of claim 1, wherein each of the plurality of demodulators comprises an in-phase I demodulator and a quadrature Q demodulator. 7. The input device of claim 1, wherein each of the plurality of demodulators is implemented digitally. 8. The input device according to claim 1, further comprising: An analog-to-digital converter ADC operates on the resultant signal before demodulating the resultant signal. 9. A processing system for an input device, The processing system includes a plurality of demodulators, and the processing system is configured to: simultaneously driving at least two of each of a plurality of transmitter electrodes disposed in a plurality of separate frequency zones in a sensing region of the input device using a plurality of transmitter signals having unique frequencies, wherein each of the plurality of separate frequency zones includes a plurality of transmitter electrodes; receiving resulting signals at receiver electrodes in the sensing region; and demodulating the resultant signal using the plurality of demodulators to generate a plurality of sensing signals, wherein each of said plurality of demodulators operates at a different one of said unique frequencies, and Wherein each of the plurality of individual frequency regions is specific to one of the unique frequencies. 10. The processing system according to claim 9, Wherein simultaneously driving at least two of each of the plurality of transmitter electrodes in each of the separate frequency zones using the plurality of transmitter signals having unique frequencies comprises: At least two of each of the plurality of transmitter electrodes are simultaneously driven in each of the plurality of separate frequency zones at one of the unique frequencies specific to the frequency zone. 11. The processing system according to claim 9, Wherein simultaneously driving at least two of each of the plurality of transmitter electrodes in each of the separate frequency zones using the plurality of transmitter signals having unique frequencies comprises: At least two of the plurality of transmitter electrodes are simultaneously driven in a first frequency zone of the plurality of separate frequency zones at a first frequency of the unique frequency, and at least two of the plurality of transmitter electrodes are simultaneously driven in a second frequency zone of the plurality of separate frequency zones at a second frequency of the unique frequency. 12. The processing system of claim 9, wherein the transmitter signals in the plurality of transmitter signals are orthogonal to each other. 13. The processing system of claim 9, wherein the plurality of transmitter signals are selected from an Orthogonal Frequency Division Multiplexing (OFDM) spectrum. 14. A method for operating an input device, the method comprising: simultaneously driving at least two of each of a plurality of transmitter electrodes disposed in a plurality of separate frequency zones in a sensing region of the input device using a plurality of transmitter signals having unique frequencies, wherein each of the plurality of separate frequency zones includes a plurality of transmitter electrodes; receiving the resulting signal at the receiver electrodes, wherein the receiver electrodes are disposed in the sensing region of the input device; demodulating the resultant signal using a plurality of demodulators to generate a plurality of sensing signals, wherein each of said plurality of demodulators operates at a different one of said unique frequencies; and wherein each of said plurality of separate frequency regions is specific to one of said unique frequencies; and Touch sensing is performed using the resultant signal. 15. A method for operating an input device, the method comprising: obtaining a plurality of non-sinusoidal transmitter signals having unique fundamental frequencies; and The sampling frequency of the analog-to-digital converter ADC is selected such that: A plurality of aliasing artifacts associated with higher harmonics of the non-sinusoidal transmitter signal are located at frequencies different from the fundamental frequency.