CN112653452B - A closed-loop RFID carrier automatic cancellation system - Google Patents
A closed-loop RFID carrier automatic cancellation system Download PDFInfo
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
- H03K3/02—Generators characterised by the type of circuit or by the means used for producing pulses
- H03K3/353—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of field-effect transistors with internal or external positive feedback
- H03K3/356—Bistable circuits
- H03K3/3562—Bistable circuits of the primary-secondary type
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
- H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
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Abstract
本发明提出一种闭环回路RFID载波自动对消系统，包括读写器发送端、读写器接收端、鉴频鉴相模块、低通带滤波器、一级信号幅度处理模块、二级信号幅度处理模块和分频器，读写器发送端连接鉴频鉴相模块第一输入端，鉴频鉴相模块输出端连接低通带滤波器输入端，低通带滤波器、一级信号幅度处理模块、二级信号幅度处理模块和分频器依次连接，一级信号幅度处理模块输出端耦接至读写器接收端，分频器输出端连接鉴频鉴相模块第二输入端，RFID读定器内部产生的载波信号分别连接一级信号幅度处理模块参考端和二级信号幅度处理模块参考端。本发明实现了发射链路泄露至接收链路的干扰信号自相消除，从而使得接收机的灵敏度得到较大提升。
The present invention proposes a closed-loop RFID carrier automatic cancellation system, including a reader transmitter, a reader receiver, a frequency detection module, a low-pass filter, a primary signal amplitude processing module, a secondary signal amplitude processing module and a frequency divider, wherein the reader transmitter is connected to the first input of the frequency detection module, the output of the frequency detection module is connected to the input of the low-pass filter, the low-pass filter, the primary signal amplitude processing module, the secondary signal amplitude processing module and the frequency divider are connected in sequence, the output of the primary signal amplitude processing module is coupled to the reader receiver, the output of the frequency divider is connected to the second input of the frequency detection module, and the carrier signal generated inside the RFID reader is respectively connected to the reference end of the primary signal amplitude processing module and the reference end of the secondary signal amplitude processing module. The present invention realizes the self-cancellation of the interference signal leaked from the transmitting link to the receiving link, thereby greatly improving the sensitivity of the receiver.
Description
Technical Field
The invention relates to the technical field of radio frequency identification, in particular to a closed loop RFID carrier automatic cancellation system.
Background
With the popularization of the Internet of things, the ultrahigh frequency radio frequency identification technology faces unprecedented historical opportunities, and the related technology is promoted to be developed and promoted at a high speed. The RFID can identify information carried on the target object label without touching, and the technology is widely applied to warehouse management systems, file management systems, logistics warehouse systems, industry 4.0 and the like.
The main technical problem at present is that the effective distance of the RFID reader for reading the tag is limited by the sensitivity of the RFID reader, and the sensitivity of the receiver is reduced because the power of a transmitting link is easy to leak into a receiving link and the receiver is interfered by a strong carrier signal when demodulating the tag signal mainly because of the limited isolation of an antenna circulator.
Therefore, the interference signal elimination of the leakage of the transmitting link to the receiving link is realized, so that the sensitivity of the receiver is greatly improved, and the key point of improving the effective distance of the RFID reader for reading the tag is that.
Disclosure of Invention
In order to solve the problems, the invention provides a closed loop RFID carrier automatic cancellation system, which realizes isolation between a transmitting link and a receiving link and has higher stability of a carrier suppression result.
The invention is realized by the following technical scheme:
The invention provides a closed loop RFID carrier wave automatic cancellation system which comprises a reader-writer transmitting end, a reader-writer receiving end, a frequency discrimination phase discrimination module, a low pass band filter, a primary signal amplitude processing module, a secondary signal amplitude processing module and a frequency divider, wherein the reader-writer transmitting end is a radio frequency signal transmitting end of an RFID reader, the reader-writer receiving end is a radio frequency signal receiving end of the RFID reader, the reader-writer transmitting end is connected with a first input end of the frequency discrimination phase discrimination module, an output end of the frequency discrimination phase discrimination module is connected with an input end of the low pass band filter, an output end of the low pass band filter is connected with an input end of the primary signal amplitude processing module, an output end of the primary signal amplitude processing module is connected with an input end of the secondary signal amplitude processing module, an output end of the primary signal amplitude processing module is coupled to the reader-writer receiving end, an output end of the secondary signal amplitude processing module is connected with an input end of the frequency divider, an output end of the frequency divider is connected with a second input end of the frequency discrimination module, and an output end of the frequency divider is connected with a reference amplitude of the RFID reader-writer and the secondary signal amplitude processing module respectively.
In the closed loop RFID carrier automatic cancellation system, the frequency discrimination phase module includes a first D flip-flop, a second D flip-flop, an exclusive-or gate, a third D flip-flop, a fourth D flip-flop, a first nand gate and a second nand gate, where the first D flip-flop clock input end is connected to the third D flip-flop clock input end and used as the first input end of the frequency discrimination phase module, the second D flip-flop clock input end is connected to the fourth D flip-flop clock input end and used as the second input end of the frequency discrimination phase module, the data input end of the first D flip-flop is connected to the reverse output end of the second D flip-flop, the first D flip-flop output end is connected to the first input end of the exclusive-or gate, the second D flip-flop output end is connected to the second input end of the exclusive-or gate, the exclusive-or gate output end is respectively connected to the third D flip-flop data input end, the fourth D flip-flop clock input end is connected to the fourth D flip-flop clock input end and used as the second input end of the frequency discrimination phase module, the data input end of the first D flip-flop and the second D flip-flop is connected to the second output end of the second nand gate, and the second output end of the second flip-flop is respectively.
Further, in the closed loop RFID carrier automatic cancellation system provided by the present invention, the first-stage signal amplitude processing module and the second-stage signal amplitude processing module have the same structure, and each of the first-stage signal amplitude processing module and the second-stage signal amplitude processing module includes a first resistor, a second resistor, a first capacitor, a second capacitor, a third capacitor and an amplifier, where a first end of the first resistor is connected to the first end of the first capacitor and the first end of the second capacitor and is used as an input end of the first-stage signal amplitude processing module or the second-stage signal amplitude processing module, a second end of the first resistor is connected to the first end of the third capacitor and the output end of the amplifier, and a positive input end of the amplifier is used as a reference end of the first-stage signal amplitude processing module or the second-stage signal amplitude processing module, and a second end of the second resistor is connected to the second end of the third capacitor and is used as an output end of the first-stage signal amplitude processing module or the second-stage signal amplitude processing module.
Further, the closed loop RFID carrier automatic cancellation system provided by the invention further comprises a power detector which is connected with the output end of the primary signal amplitude processing module and is used for detecting the carrier automatic cancellation effect.
Further, in the closed loop RFID carrier automatic cancellation system provided by the invention, the power detector comprises an AD8312 chip.
Further, in the closed loop RFID carrier auto-cancellation system provided by the present invention, the frequency divider includes a fifth D flip-flop, the clock input end of the fifth D flip-flop is used as the input end of the frequency divider, the inverted output end of the fifth D flip-flop is connected to the data input end thereof, and the output end of the fifth D flip-flop is used as the output end of the frequency divider.
Further, the closed loop RFID carrier automatic cancellation system further comprises a directional coupler and an antenna, wherein the input end of the directional coupler is connected with the transmitting end of the reader-writer, the output end of the directional coupler is connected with the receiving end of the reader-writer, and the coupling end of the directional coupler is connected with the antenna.
Further, in the closed loop RFID carrier automatic cancellation system provided by the invention, the output signal of the directional coupler is overlapped with the output signal of the primary signal amplitude processing module and then is input to the receiving end of the reader-writer.
The invention has the beneficial effects that:
The present invention proposes a new carrier loop suppression scheme to eliminate the influence of the transmit power on the receive circuitry. Through verification, the scheme of the invention has higher stability of the carrier suppression result and simple structure, and realizes self-phase elimination of interference signals leaked from a transmitting link to a receiving link, thereby greatly improving the sensitivity of a receiver.
Drawings
FIG. 1 is a schematic diagram of the overall structure of an embodiment of the present invention;
Fig. 2 is a schematic diagram of a frequency and phase discrimination module according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a primary signal amplitude processing module or a secondary signal amplitude processing module according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a frequency divider according to an embodiment of the invention.
Detailed Description
In order to more clearly and completely describe the technical scheme of the invention, the invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the embodiment of the closed loop RFID carrier automatic cancellation system provided by the invention includes a reader-writer transmitting end 101, a reader-writer receiving end 102, a frequency discrimination phase discrimination module 103, a low pass filter 104, a first-stage signal amplitude processing module 105, a second-stage signal amplitude processing module 106 and a frequency divider 107, wherein the reader-writer transmitting end 101 is a radio frequency signal transmitting end of an RFID reader, the reader-writer receiving end 102 is a radio frequency signal receiving end of the RFID reader, the reader-writer transmitting end 101 is connected with a first input end of the frequency discrimination phase discrimination module 103, an output end of the frequency discrimination phase discrimination module 103 is connected with an input end of the low pass filter 104, an output end of the low pass filter 104 is connected with an input end of the first-stage signal amplitude processing module 105, an output end of the first-stage signal amplitude processing module 105 is connected with an input end of the second-stage signal amplitude processing module 106, an output end of the first-stage signal amplitude processing module 105 is coupled to the reader-writer receiving end 102, an output end of the second-stage signal amplitude processing module 106 is connected with an input end of the frequency divider 107, an output end of the frequency divider 107 is connected with a second input end of the frequency discrimination phase discrimination module 103, and an output end of the first-stage signal generated inside the reader is respectively connected with an input end of the second-stage signal amplitude processing module 106 and a reference end of the second-stage signal amplitude processing module 106.
In this embodiment, after the command is sent, the reader-writer sending end 101 of the RFID reader-writer still transmits a carrier wave for providing energy for the tag, and the carrier wave leaks a part of carrier wave to the reader-writer receiving end 102 through the circulator, and meanwhile, a part of carrier wave is coupled into the frequency and phase discrimination module 103 of this embodiment, the frequency and phase discrimination module 103 carries out detection and phase comparison on the carrier wave fed back by the frequency divider 107 and the carrier wave leaked from the circulator, then outputs the carrier wave, the phase comparison signal is changed into a direct current voltage signal by the low pass filter 104, the direct current voltage signal carries out inversion on the input carrier wave generated by the carrier wave input module by controlling the primary signal amplitude processing module 105, then carries out signal recovery again by controlling the secondary signal amplitude processing module 106, the frequency divider 107 feeds back the output carrier wave signal to the frequency and phase discrimination module 103, and at this time, the carrier wave signal output by the primary signal amplitude processing module 105 and the circulator leak a part of carrier wave model number of the reader-writer receiving end 102 are opposite in amplitude and phase, and the purpose of closed loop automatic addition to the reader-writer receiving end 102 is achieved.
The carrier automatic cancellation system scheme of the embodiment of the invention is different from the traditional scheme phase shifting scheme, and the invention firstly realizes the synchronous self-alignment of the phases of the receiving link and the transmitting link through phase discrimination, loop filtering, intrinsic carrier and frequency division loop, then carries out amplitude deflection and attenuation so as to feed into the receiving link, and further realizes the self-alignment cancellation of the phases of the carrier leakage of the receiving link, thereby greatly improving the sensitivity of the receiver. When the transmitting power of the transmitting end of the reader-writer is increased, the carrier power leaked to the receiving end of the reader-writer is gradually increased, and the carrier signal is restrained by about 45dB as a whole, and the sensitivity of the receiving end of the scheme is improved by about 35dB compared with that of the conventional scheme. Meanwhile, the invention solves the problem of poor cancellation stability in the prior art, and realizes the isolation between the transmitting link and the receiving link.
Further, referring to fig. 2, in an embodiment of a closed loop RFID carrier automatic cancellation system, the phase discriminator module 103 includes a first D flip-flop 1031, a second D flip-flop 1032, an exclusive-or gate 1033, a third D flip-flop 1034, a fourth D flip-flop 1035, a first nand gate 1036 and a second nand gate 1037, where a clock input end of the first D flip-flop 1031 is connected to a clock input end of the third D flip-flop 1034 and is used as a first input end of the phase discriminator module 103, a clock input end of the second D flip-flop 1032 is connected to a clock input end of the fourth D flip-flop 1035 and is used as a second input end of the phase discriminator module 103, a data input end of the first D flip-flop 1031 is connected to a reverse output end of the first D flip-flop 1031, a data input end of the second D flip-flop 1034 is connected to a first input end of the exclusive-or gate 1033, an output end of the second D flip-flop 1031032 is connected to a second input end of the exclusive-or gate 1033, an output end of the second D flip-flop 1033 is connected to a second input end of the third D flip-flop 1034, an output end of the fourth D flip-flop 1035 is connected to a data input end of the second D flip-flop 1036, and is connected to a second output end of the second D flip-flop 1037.
In this embodiment, the two input signals of the phase demodulation module 103 are pulse sequences, and the leading edge or the trailing edge thereof represents the respective phases. The output related to the phase difference can be obtained by comparing the frequency and the phase of the two pulse sequences, and the module adopts multistage cascade and synchronous processing, thereby meeting the requirements of a cancellation system.
Further, referring to fig. 3, in an embodiment of a closed loop RFID carrier automatic cancellation system, the first-stage signal amplitude processing module 105 and the second-stage signal amplitude processing module 106 have the same structure, and each include a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, and an amplifier, where a first end of the first resistor R1 is connected to a first end of the first capacitor C1 and a first end of the second capacitor C2 and is used as an input terminal Vin of the first-stage signal amplitude processing module 105 or the second-stage signal amplitude processing module 106, a second end of the first resistor R1 is connected to a first end of the third capacitor C3 and a negative input terminal of the amplifier, a positive input terminal of the amplifier is used as a reference terminal Vref of the first-stage signal amplitude processing module 105 or the second-stage signal amplitude processing module 106, a second end of the first capacitor C1 is grounded, a second end of the second capacitor is connected to a first end of the second resistor R2, and a second end of the second resistor R2 is connected to a second end of the third capacitor C3 and an output terminal of the amplifier and is used as an output terminal Vout of the first-stage signal amplitude processing module 105 or the second-stage signal amplitude processing module 106.
In this embodiment, the amplitude processing module should always feed the output of the charge pump directly into the high Q capacitor, i.e. the capacitor with the smallest series resistance, before the high frequency content is fed into the loop filter op amp. The reason for this is that the op-amp has a limited bandwidth and if driven directly by high frequencies may exhibit nonlinear behavior such as those present in the charge pump output. Furthermore, the feedback of the operational amplifier should be configured to achieve unity gain from the operational amplifier terminal to its output. In this way, the reference noise input to the operational amplifier does not affect the loop filter output and is therefore not amplified.
Further, in an embodiment of the closed loop RFID carrier auto-cancellation system, the system further includes a power detector connected to an output end of the primary signal amplitude processing module 105, for detecting an auto-cancellation effect of the carrier. The automatic cancellation effect of the carrier signal according to the embodiments of the present invention may be reflected by detecting the output signal of the primary signal amplitude processing module 105 by the power detector.
Further, in an embodiment of the closed loop RFID carrier auto-cancellation system, the power detector includes an AD8312 chip. The first pin of AD8312 chip is connected with the power, and second pin and third pin are as testing result output, and fourth pin and fifth pin ground, and the sixth pin is as the detected signal input.
Further, referring to fig. 4, in an embodiment of the closed loop RFID carrier auto-cancellation system, the frequency divider 107 includes a fifth D flip-flop, a clock input terminal of the fifth D flip-flop is used as an input terminal of the frequency divider 107, an inverting output terminal of the fifth D flip-flop is connected to a data input terminal thereof, and an output terminal of the fifth D flip-flop is used as an output terminal of the frequency divider 107.
In the present embodiment, the frequency divider 107 uses a D flip-flop in the chain as the frequency division of the two counters. A D flip-flop divides the clock frequency into one half and if two flip-flops are used, the clock frequency into one quarter. One benefit of using a bistable flip-flop to divide is that the output at any point has a precise 50% duty cycle, changing the dividing equal of the loop according to the frequency change in the link, thereby achieving phase synchronization of the loop.
Further, referring to fig. 1, in an embodiment of the closed loop RFID carrier automatic cancellation system, the system further includes a directional coupler 108 and an antenna 109, an input end of the directional coupler 108 is connected to the reader-writer transmitting end 101, an output end of the directional coupler 108 is connected to the reader-writer receiving end 102, and a coupling end of the directional coupler 108 is connected to the antenna 109.
Further, referring to fig. 1, in an embodiment of a closed loop RFID carrier automatic cancellation system, an output signal of the directional coupler 108 is added to an output signal of the primary signal amplitude processing module 105 and then input to the reader-writer receiving end 102.
In summary, the present invention proposes a new carrier loop suppression scheme to eliminate the influence of the transmit power on the receiving circuit. Through verification, the scheme of the invention has higher stability of the carrier suppression result and simple structure, and realizes self-phase elimination of interference signals leaked from a transmitting link to a receiving link, thereby greatly improving the sensitivity of a receiver.
Of course, the present invention can be implemented in various other embodiments, and based on this embodiment, those skilled in the art can obtain other embodiments without any inventive effort, which fall within the scope of the present invention.
Claims (7)
1. The closed loop RFID carrier automatic cancellation system is characterized by comprising a reader-writer transmitting end (101), a reader-writer receiving end (102), a frequency discrimination phase discrimination module (103), a low pass band filter (104), a first-stage signal amplitude processing module (105), a second-stage signal amplitude processing module (106) and a frequency divider (107), wherein the reader-writer transmitting end (101) is a radio frequency signal transmitting end of an RFID reader, the reader-writer receiving end (102) is a radio frequency signal receiving end of the RFID reader, the reader-writer transmitting end (101) is connected with a first input end of the frequency discrimination phase discrimination module (103), an output end of the frequency discrimination phase discrimination module (103) is connected with an input end of the low pass band filter (104), an output end of the low pass band filter (104) is connected with an input end of the first-stage signal amplitude processing module (105), an output end of the first-stage signal amplitude processing module (105) is connected with an input end of the second-stage signal amplitude processing module (106), an output end of the first-stage signal amplitude processing module (105) is coupled to a first input end of the RFID reader-writer, an output end of the second-stage signal amplitude processing module (103) is connected with an output end of the second-stage signal amplitude processing module (107), the carrier signal generated in the RFID reader is respectively connected with the reference end of the primary signal amplitude processing module (105) and the reference end of the secondary signal amplitude processing module (106);
The primary signal amplitude processing module (105) and the secondary signal amplitude processing module (106) have the same structure and comprise a first resistor (R1), a second resistor (R2), a first capacitor (C1), a second capacitor (C2), a third capacitor (C3) and an amplifier, wherein a first end of the first resistor (R1) is connected with a first end of the first capacitor (C1) and a first end of the second capacitor (C2) and is used as an input end (Vin) of the primary signal amplitude processing module (105) or the secondary signal amplitude processing module (106), a second end of the first resistor (R1) is connected with a first end of the third capacitor (C3) and a negative input end of the amplifier, a positive input end of the amplifier is used as a reference end (Vref) of the primary signal amplitude processing module (105) or the secondary signal amplitude processing module (106), a second end of the first capacitor (C1) is grounded, a second end of the second capacitor is connected with a first end of the second resistor (R2), and a second end of the second resistor (R2) is connected with a first end of the second capacitor (C3) and is used as an output end of the primary signal amplitude processing module (106);
After an instruction is sent, the reader-writer sending end (101) always sends a carrier wave to provide energy for a tag, the carrier wave leaks a part of the carrier wave to the reader-writer receiving end (102) through the circulator, meanwhile, a part of the carrier wave enters the frequency discrimination phase discrimination module (103) through coupling, the frequency discrimination phase discrimination module (103) carries out detection and phase comparison on the carrier wave signal fed back by the frequency divider (107) and the carrier wave signal leaked by the circulator, the phase comparison signal is changed into a direct-current voltage signal through the low pass filter (104), the direct-current voltage signal turns over an input carrier wave generated by the carrier wave input module through controlling the primary signal amplitude processing module (105), the signal is restored through the secondary signal amplitude processing module (106), the frequency divider (107) feeds back the output carrier wave signal to the frequency discrimination phase discrimination module (103), the carrier wave signal output by the primary signal amplitude processing module (105) after loop processing and the circulator leak a part of the carrier wave model of the carrier wave to the reader-writer receiving end (102) are opposite in amplitude, and the carrier wave model is overlapped to the carrier wave model of the same phase, and the reader-writer receiving end (102) automatically carries out closed loop cancellation.
2. The system of claim 1, wherein the phase and frequency discrimination module (103) comprises a first D flip-flop (1031), a second D flip-flop (1032), an exclusive-or gate (1033), a third D flip-flop (1034), a fourth D flip-flop (1035), a first nand gate (1036) and a second nand gate (1037), the first D flip-flop (1031) has a clock input connected to the third D flip-flop (1034) and serving as a first input of the phase and frequency discrimination module (103), the second D flip-flop (1032) has a clock input connected to the fourth D flip-flop (1035) and serving as a second input of the phase and frequency discrimination module (103), the first D flip-flop (1031) has a data input connected to its inverting output, the second D flip-flop (1032) has a data input connected to its inverting output, the first D flip-flop (1031) has a data input connected to the second D flip-flop (1033) and the second or gate (1036) has a data input connected to the first D flip-flop (1034) and the second D flip-flop (1035) and the data input of the fourth D flip-flop (1036), the reflection output end of the third D trigger (1034) is respectively connected with the setting end of the fourth D trigger (1035) and the first input end of the second NAND gate (1037), the output end of the fourth D trigger (1035) is respectively connected with the reset end of the third D trigger (1034) and the second input end of the first NAND gate (1036), the output end of the first NAND gate (1036) is connected with the second input end of the second NAND gate (1037), and the output end of the second NAND gate (1037) is used as the output end of the frequency discrimination phase discrimination module (103).
3. A closed loop RFID carrier auto-cancellation system as claimed in claim 1, further comprising a power detector coupled to an output of the primary signal amplitude processing module (105) for detecting carrier auto-cancellation effects.
4. A closed loop RFID carrier auto-cancellation system as claimed in claim 3 wherein the power detector comprises an AD8312 chip.
5. A closed loop RFID carrier auto-cancellation system according to claim 1, characterized in that the frequency divider (107) comprises a fifth D flip-flop, the clock input of which is the input of the frequency divider (107), the inverting output of which is connected to the data input of which, the output of which is the output of the frequency divider (107).
6. A closed loop RFID carrier auto-cancellation system according to claim 1, further comprising a directional coupler (108) and an antenna (109), wherein an input of the directional coupler (108) is connected to the reader/writer transmitter (101), an output of the directional coupler (108) is coupled to the reader/writer receiver (102), and a coupling of the directional coupler (108) is connected to the antenna (109).
7. A closed loop RFID carrier auto-cancellation system as claimed in claim 6, wherein,
And the output signal of the directional coupler (108) is overlapped with the output signal of the primary signal amplitude processing module (105) and then is input into the receiving end (102) of the reader-writer.
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| CN114595792B (en) * | 2022-05-10 | 2022-08-16 | 深圳市国芯物联科技有限公司 | UHFRFID reader including channel selection filter supporting dual protocols |
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| US20090196373A1 (en) * | 2008-01-31 | 2009-08-06 | Skyetek, Inc. | System for increasing rfid tag reader sensitivity |
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