CN114531171B

CN114531171B - Radio frequency front-end circuit with embedded filter

Info

Publication number: CN114531171B
Application number: CN202210432737.5A
Authority: CN
Inventors: 王晗
Original assignee: Anhui Xilei Electronic Technology Co ltd
Current assignee: Anhui Xilei Electronic Technology Co ltd
Priority date: 2022-04-24
Filing date: 2022-04-24
Publication date: 2022-07-05
Anticipated expiration: 2042-04-24
Also published as: CN114531171A

Abstract

The invention provides a radio frequency front-end circuit with an embedded filter, wherein an input port of the radio frequency front-end circuit is connected with a first end of a capacitor C4 through inductors L3 and L4 which are sequentially connected, and a series branch consisting of a capacitor C5 and a switch S3 is connected in parallel with two ends of an L4; a series branch formed by a capacitor C6 and a switch S4 is connected in parallel at two ends of an L3, a connection point of the L3 and the L4 is connected with a reference potential through an inductor L5 and a capacitor C7 which are sequentially cascaded, and a connection point of the L3 and the L4 is connected with the reference potential through a switch S5 and a capacitor C8 which are sequentially cascaded; the input port is further connected with a control end of a switch S1 through an inductor L1 and a capacitor C1 which are sequentially connected, one end of the switch S1 is grounded, the other end of the switch S1 is respectively connected with a first end of an inductor L2 and a first end of a capacitor C2, a second end of the L2 and a first end of the C3 are both connected to a power supply voltage VDD, the C2 is connected with a second end of the C3 and then connected with one end of a switch S2, and the other end of the S2 is connected with a first end of a capacitor C4. The invention avoids the insertion loss of the filter and improves the performance of the wireless transceiving system.

Description

Radio frequency front-end circuit with embedded filter

Technical Field

The present invention relates to the field of communications, and in particular, to a radio frequency front end circuit with an embedded filter.

Background

With the development of communication technology and chip technology, the rf front end of the integrated rf switch and amplifier has become one of the important modules in the wireless rf communication system. A common radio frequency front end includes a low noise amplifier for the receive chain and a radio frequency switch for the transmit chain. When the main chip works in a transmitting mode, a transmitting power signal is transmitted to the antenna port through the radio frequency switch. Because the power transmission at the antenna port needs to meet strict requirements for spectral spurs, a series filter is often added at the antenna port to filter spurs in a transmission signal in a transmission mode, so that the transmission signal can meet different requirements of various countries on the spectral spurs. However, the introduction of the filter affects the transmission power and the sensitivity in the receiving mode, mainly due to the insertion loss of the filter itself, so that the transceiving performance is degraded.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a radio frequency front-end circuit with an embedded filter, wherein a harmonic spurious filter is embedded in a radio frequency switch, so that the insertion loss of the filter cannot influence the transmitting power and the sensitivity in a receiving mode, and the performance of a wireless transceiving system is improved.

To achieve the above object, the present invention provides a rf front-end circuit with embedded filter, the rf front-end circuit including an input port (IN) and an output port (OUT), comprising:

the input port is connected with a first end of a fourth capacitor C4 through a fourth inductor L4 and a third inductor L3 which are connected in sequence, and a second end of the fourth capacitor C4 is used as the output port; a series branch consisting of the fifth capacitor C5 and the third switch S3 is connected in parallel to two ends of the fourth inductor L4; a series branch formed by a sixth capacitor C6 and a fourth switch S4 is connected in parallel with two ends of a third inductor L3, a connection point of the inductors L3 and L4 is connected with a reference potential through a fifth inductor L5 and a seventh capacitor C7 which are sequentially cascaded, and a connection point of the inductors L3 and L4 is connected with the reference potential through a fifth switch S5 and an eighth capacitor C8 which are sequentially cascaded;

the input port is further connected with a control end of a first switch S1 through a first inductor L1 and a first capacitor C1 which are connected in sequence, one end of the first switch S1 is grounded, the other end of the first switch S1 is connected with a first end of a second inductor L2 and a first end of a second capacitor C2 respectively, a second end of the second inductor L2 and a first end of a third capacitor C3 are both connected to a power supply voltage VDD, a second end of the second capacitor C2 is connected with a second end of a third capacitor C3 and then connected to one end of a second switch S2, and the other end of the second switch S2 is connected with a first end of a fourth capacitor C4;

the radio frequency front-end circuit has two working modes as follows:

when the band-pass filter works in a transmitting mode, S3 and S4 are connected, S1, S2 and S5 are disconnected, C5, C6, L3, L4, C7 and L5 form a fifth-order band-pass filter, wherein L3 and C6, L4 and C5 are parallel resonant networks respectively, and C7 and L5 are series resonant networks respectively providing zeros of the band-pass filter at different frequencies;

when operating in the receive mode, switches S3 and S4 are open and switches S1, S2, S5 are closed.

Further, the input port is coupled to a communication antenna; the output port is used as a communication transceiving interface of the front-end module and is coupled and connected to a receiving port and a transmitting port of the rear-stage circuit.

The control ends of the switches S3 and S4 are connected with a receiving and sending switching control signal CT, and the control ends of the switches S2 and S5 are connected with an enable signal EN; the switches S1-S5 may be transistors or transistors.

Further, the reference potential is ground GND;

further, both ends of the switch S2 are also pulled up to the power supply voltage VDD through the first resistor and the second resistor, respectively.

Further, a mode switching controller is included for providing control signals to the control terminals of the switches S2-S5.

The invention also provides a communication module which comprises one or more radio frequency front-end circuits.

The technical scheme provided by the invention creatively provides a radio frequency front-end circuit with an embedded filter, and the harmonic spurious filter is embedded in a radio frequency switch, so that the insertion loss of the filter cannot influence the transmitting power and the sensitivity in a receiving mode, and the performance of a wireless transceiving system is improved.

Compared with the conventional rf front-end circuit, the beneficial effects are specifically listed as follows:

1) the invention embeds a fifth-order band-pass filter for filtering harmonic waves and transmitting stray waves in a transmitting link;

2) by constructing the resonant network, the parasitic capacitance of the switching tube (S3, S4) is absorbed by the parallel resonance (L3 and C6, L4 and C5), and the parasitic capacitance of the switching tube (S5) which improves the isolation effect is absorbed by the series resonance (C7 and L5), so that the overall insertion loss of the transmitting link is effectively reduced;

3) the blocking capacitors of the switching tubes (S3 and S4) can be used as a part of a fifth-order band-pass filter, so that multiplexing is achieved, and the influence of the blocking capacitors on insertion loss is reduced.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the example serve to explain the principles of the invention and not to limit the invention.

Fig. 1 is a schematic diagram of an rf front-end circuit in the prior art;

fig. 2 is a schematic diagram of an improved rf front-end circuit according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

As shown in fig. 1, a conventional rf front-end circuit is shown. The radio frequency front end circuit comprises a transmitting link and a receiving link, wherein S4 is a radio frequency switch used for the transmitting link; the inductor L1, L2, the capacitor C2, C5, C6, C7 and the transistor S2 form a low noise amplifier for the receiving link. The drain of the S4 is connected with one end of an inductor L1, the other end of the L1 is connected with the gate of the S1 through a capacitor C2, and the source of the S4 is connected with the OUT port through the capacitor C7; the drain of S1 is connected to one end of C5 and one end of L2 respectively, the other end of L2 is connected to the other end of C5 and the source of S2 through capacitor C6, and the drain of S2 is connected to the source of S4. When the switch tube S4 is turned off and the transistors S1 and S2 are turned on, the rf front end operates in a receiving mode; when S1, S2 are turned off and S4 is turned on, the rf front end operates IN a transmit mode, and transmit power is transmitted to an IN port, typically an antenna port of a wireless transceiver module, through an OUT port.

A band-pass filter B1 is connected between the antenna port and the drain of S4 in series. The band-pass filter B1 is used to filter the spurious and harmonic of the transmission signal transmitted from the main chip in the transmission mode, so as to meet the strict requirement of spectral spurious. But the filter itself has power loss, and its introduction affects the transmission power and the sensitivity in the reception mode, thereby degrading the transceiving performance.

In order to make up for the above deficiencies, the invention improves the prior art, and provides a radio frequency front-end circuit with an embedded filter and a specific design, thereby realizing embedding the harmonic spurious filter in the radio frequency switch, so that the insertion loss of the filter does not influence the transmitting power and the sensitivity in a receiving mode, and improving the performance of a wireless transceiving system.

Fig. 2 is a schematic diagram of an rf front-end circuit of an improved embedded filter according to an embodiment of the present invention, as shown in the drawing: the antenna port IN is connected with a first end of a capacitor C4 through an inductor L4 and an inductor L3 which are connected IN sequence, and a second end of the capacitor C4 is used as a communication interface of the front-end module, namely an RX/TX port; a series branch consisting of the capacitor C5 and the switch S3 is connected in parallel at two ends of the L4; a series branch formed by the capacitor C6 and the switch S4 is connected in parallel at two ends of the L3, a connection point of the inductor L3 and the inductor L4 is connected with a reference potential through the inductor L5 and the capacitor C7 which are sequentially cascaded, and a connection point of the inductor L3 and the inductor L4 is connected with the reference potential through the switch S5 and the capacitor C8 which are sequentially cascaded. The control ends of the switches S3 and S4 are connected to a transceiving switching control signal CT, the control end of the switch S5 is connected to an enable signal EN, the switches S3-S5 may be transistors or transistors, and the control end is a gate or a base thereof, respectively. The reference potential is ground GND.

The antenna port IN is further connected to a control terminal of the switch S1 through the sequentially connected L1 and C1, one end (e.g., the source S) of the switch S1 is grounded, the other end (e.g., the drain D) of the switch S1 is connected to the first end of the inductor L2 and the first end of the capacitor C2, the second end of the inductor L2 and the first end of the capacitor C3 are both connected to the power supply voltage VDD, the second end of the capacitor C2 is connected to the second end of the capacitor C3 and then connected to one end (e.g., the source S) of the switch S2, and the other end of the switch S2 is connected to the first end of the capacitor C4. The control terminal of the switch S2 is connected to an enable signal EN, and the switches S1-S2 may be transistors or transistors, and the control terminal is the gate or the base thereof, respectively. In addition, the two terminals of the switch S2 are also pulled up to the power voltage VDD through the first resistor R4 and the second resistor R5, respectively.

The working principle of the invention is as follows: the capacitors C5-C8, the inductors L3-L5 and the switch tubes S3-S5 jointly form a transmitting switch link of the embedded filter; when S3 and S4 are turned on and S1, S2 and S5 are turned off, C5, C6, L3, L4, C7 and L5 form a five-order band-pass filter, wherein L3, C6 and L4 are parallel resonances respectively, C5 is series resonances respectively, and C7 and L5 are series resonances respectively, and zero points of the band-pass filter at different frequencies are respectively provided. In this way, the filter is used as a part of a transmitting link, parasitic capacitances of the switching tubes S3 and S4 are absorbed by the parallel resonance L3, C6, L4 and C5, and parasitic capacitances of the switching tubes S5 which improve the isolation are absorbed by the series resonance C7 and L5, so that the overall insertion loss of the transmitting link is effectively reduced. Meanwhile, the blocking capacitors of the switching tubes S3 and S4 can be used as a part of a fifth-order band-pass filter, so that the influence of the blocking capacitors on insertion loss is reduced.

When the radio frequency front end works in a receiving mode, the switch tubes S3 and S4 are disconnected, the switch tubes S1, S2 and S5 are connected, and the C8 provides a low-resistance point, so that the isolation is effectively improved, and the normal work of a receiving link cannot be influenced by a transmitting link.

In order to overcome the defects of the traditional radio frequency front-end circuit, the invention designs an innovative circuit architecture, and constructs a required filter by multiplexing devices on a transmitting path, thereby effectively transferring insertion loss caused by introducing the filter and improving the transceiving performance of a communication system. The radio frequency front-end circuit can be applied to various communication modules, communication devices and communication systems according to actual needs. And a mode control module for switching the transceiving mode.

Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the present invention should be determined by the following claims.

Claims

1. A rf front-end circuit with embedded filter, said rf front-end circuit comprising an input port (IN) and an output port (OUT), characterized IN that:

the radio frequency front-end circuit has two working modes as follows:

2. The RF front-end circuit of claim 1, wherein the switches S3 and S4 are controlled by a transmit/receive switching control signal CT, and the switches S2 and S5 are controlled by an enable signal EN.

3. The RF front-end circuit of claim 1, wherein the switches S1-S5 may be switches or transistors.

4. The rf front-end circuit of claim 1, wherein the switch S2 is further coupled to pull up the supply voltage VDD through a first resistor and a second resistor, respectively.

5. The RF front-end circuit of any one of claims 1-4, further comprising a mode switch controller for providing control signals to the control terminals of the switches S2-S5.

6. A communications module comprising one or more radio frequency front end circuits as claimed in any one of claims 1 to 4.