Coupled-line based RF front end

Abstract

The present invention discloses a radio frequency front end based on a coupling line, including a transmitting branch and a receiving branch, the transmitting branch includes a differential power amplifier, a first coupling line and a second coupling line, the differential power amplifier includes a first transistor and a second transistor, the output end of the first transistor is connected to the first coupling line, the output end of the second transistor is connected to the second coupling line, the first coupling line is connected to an antenna, and the first coupling line and the second coupling line are connected; the receiving branch includes a low noise amplifier and a transceiver switch, and the second coupling line is connected to the transceiver switch. The present invention reduces the transmission loss by removing the transmitting switch, thereby significantly improving the transmission efficiency. Secondly, the coupling line balun fully absorbs the parasitic parameters of the transistor and provides an impedance transformation function, so that the use of an additional PA output network can be avoided, which helps to further improve the PA efficiency.

Description

Technical Field

[0001] The present invention relates to the field of communication systems, and in particular to a radio frequency front end based on coupled lines. Background Art

[0002] The power amplifier (PA) is the core component in the RF transceiver, and its efficiency has a great impact on the overall power consumption. In the time division duplexing (TDD) communication system and the phased array radar system, the transmitter and the receiver work in different time slots and share the same antenna. This requires the use of a single pole double throw (SPDT) switch as a transceiver switch to switch the connection between the PA and the low noise amplifier (LNA) and the antenna. The circuit composed of PA, LNA and the transceiver SPDT switch is called the RF front end. The design of the traditional RF front end is relatively simple. After the PA, LNA and SPDT switch are designed independently, the three can be connected. However, the SPDT switch will introduce additional insertion loss, and its insertion loss increases sharply with the increase of frequency, resulting in a significant decrease in the efficiency of the PA in the transmit mode (hereinafter referred to as the transmit efficiency). Summary of the invention

[0003] In view of the problem of deteriorated transmission efficiency in traditional radio frequency front ends, the present invention proposes a radio frequency front end based on coupled lines, and significantly improves the transmission efficiency by removing the switch of the transmission branch.

[0004] A radio frequency front end based on coupling lines comprises a transmitting branch and a receiving branch, wherein the transmitting branch comprises a differential power amplifier, a first coupling line and a second coupling line, wherein the differential power amplifier comprises a first transistor and a second transistor, wherein the output end of the first transistor is connected to the first coupling line, and the output end of the second transistor is connected to the second coupling line, wherein the first coupling line is connected to an antenna, and the first coupling line and the second coupling line are connected; wherein the receiving branch comprises a low noise amplifier and a transceiver switch, and the second coupling line is connected to the transceiver switch.

[0005] Furthermore, the first transistor and the second transistor are field effect transistors or bipolar transistors.

[0006] Furthermore, the drains of the first transistor and the second transistor of the differential power amplifier are respectively connected to a parasitic capacitor, and the other end of the parasitic capacitor is grounded; and the sources of the first transistor and the second transistor are both grounded.

[0007] Furthermore, the first coupling line includes a first transmission line and a second transmission line coupled to each other, the drain of the first transistor is connected to the first transmission line, and the other end of the first transmission line is grounded; one end of the second transmission line is connected to the second coupling line, and the other end is connected to the antenna, and a load capacitor C is provided between the antenna and the second transmission line. L , the load capacitance C L The other end is grounded.

[0008] Furthermore, the second coupling line includes a third transmission line and a fourth transmission line coupled to each other, the drain of the second transistor is connected to the third transmission line, and the other end of the third transmission line is grounded; one end of the fourth transmission line is connected to the second transmission line, and the other end is connected to the transceiver switch.

[0009] Preferably, the transceiver switch includes a switch and a parasitic capacitor connected in parallel therewith.

[0010] Preferably, the transceiver switch is connected to an input end of the low noise amplifier.

[0011] The RF front end is configured such that, in the transmission mode, the transceiver switch is closed, the low noise amplifier is turned off, the output parasitic capacitance of the first coupling line, the second coupling line and the transistor in the differential power amplifier, and the load capacitance C L The coupled line balun is formed, and the antenna impedance is Z ANT The coupled line balun is converted into an optimal load impedance R for the first transistor and the second transistor. opt .

[0012] The RF front end is configured such that, in the receiving mode, the transceiver switch is disconnected, the differential power amplifier is turned off, the output impedance of the first transistor and the second transistor is short-circuited, and the parasitic capacitance of the first coupling line, the second coupling line, the switch and the load capacitance C L Form a capacitor loaded transmission line.

[0013] Furthermore, the output impedance of the first transistor and the second transistor is short-circuited by closing the drain voltage and increasing the gate voltage.

[0014] Compared with the traditional RF front end, the RF front end structure based on coupled lines proposed in the present invention has obvious advantages. First, by removing the transmitting switch, the transmission loss is reduced, thereby significantly improving the transmission efficiency. Secondly, the coupled line balun can fully absorb the parasitic parameters of the transistor and provide an impedance transformation function, so the use of an additional PA output network can be avoided, which helps to further improve the PA efficiency. Finally, the coupled line has the advantages of broadband, low loss, and compact size, which can improve the comprehensive performance of the RF front end and has a good application prospect in TDD communication systems and phased array radar systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 This is a schematic diagram of the structure of a radio frequency front end based on coupled lines according to an embodiment of the present invention;

[0017] Figure 2 for Figure 1 An equivalent circuit diagram of the radio frequency front end of the embodiment in the transmission mode;

[0018] Figure 3 for Figure 1 Equivalent circuit diagram of the radio frequency front end of the embodiment in the receiving mode. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0020] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0021] The RF front end based on coupled lines proposed by the present invention is as follows Figure 1 As shown, it includes a transmitting branch and a receiving branch, wherein the transmitting branch includes a differential power amplifier, a first coupling line and a second coupling line, the differential power amplifier includes a first transistor and a second transistor, the output end of the first transistor is connected to the first coupling line, the output end of the second transistor is connected to the second coupling line, the first coupling line is connected to the antenna, and the first coupling line is connected to the second coupling line. The receiving branch includes a low noise amplifier and a transceiver switch, and the second coupling line is connected to the transceiver switch.

[0022] The first transistor and the second transistor can be a field effect transistor (FET) or a bipolar junction transistor (BJT). When FET is used, it can be a common source transistor or a stack structure composed of common source and common gate transistors. When BJT is used, it can be a common emitter transistor or a stack structure composed of common emitter and common base transistors. The above are all common PA transistor structures. Those skilled in the art understand their structure and composition, which can be directly applied in this embodiment.

[0023] In this embodiment, the drains of the first transistor and the second transistor of the differential power amplifier are respectively connected to a parasitic capacitor, and the other end of the parasitic capacitor is grounded; the sources of the first transistor and the second transistor are both grounded. The transceiver switch includes a switch and a parasitic capacitor connected in parallel therewith. Figure 1 Medium R opt represents the optimum load impedance of the PA transistor, C dev represents the output parasitic capacitance of the PA transistor, C SW Represents the parasitic capacitance of the transceiver switch S1. The main difference from the traditional RF front end is that in the RF front end based on coupled lines, the PA, LNA and transceiver switch are integrated into one design, and an independent SPDT switch is no longer used as the transceiver switch.

[0024] Furthermore, the first coupling line includes a first transmission line and a second transmission line coupled to each other, the drain of the first transistor is connected to the first transmission line, and the other end of the first transmission line is grounded; one end of the second transmission line is connected to the second coupling line, and the other end is connected to the antenna, and a load capacitor C is provided between the antenna and the second transmission line. L , load capacitance C L The other end is grounded.

[0025] Similarly, the second coupling line includes a third transmission line and a fourth transmission line coupled to each other, the drain of the second transistor is connected to the third transmission line, and the other end of the third transmission line is grounded; one end of the fourth transmission line is connected to the second transmission line, and the other end is connected to the transceiver switch.

[0026] The RF front end of this embodiment is in the transmitting mode, the transceiver switch is closed, and the low noise amplifier is turned off. The equivalent circuit of the RF front end of this embodiment is as follows: Figure 2 Specifically, the output parasitic capacitance C of the first coupling line, the second coupling line and the differential power amplifier transistor (the first transistor and the second transistor) is dev , and the load capacitance C L The coupled line balun is composed of a coupled line balun, which simultaneously performs the functions of differential to single-ended conversion and output impedance transformation. The antenna impedance Z ANT The coupled line balun is converted into an optimal load impedance R for the first transistor and the second transistor. opt .

[0027] In the receiving mode, the transceiver switch S1 is disconnected, the differential power amplifier is turned off, and the output impedance of the first transistor and the second transistor is short-circuited. The equivalent circuit of the RF front end of this embodiment is as follows: Figure 3 The output short circuit of the PA transistor can be achieved by closing the drain voltage and increasing the gate voltage. The parasitic capacitance C of the first coupling line, the second coupling line, and the switch SW and load capacitance C L By adjusting the parameters of the coupling line and C SW and C L The capacitance value can make the characteristic impedance of the capacitor-loaded transmission line close to the antenna Z ANT , thereby avoiding the impact of capacitively loaded transmission lines on the input matching of the LNA.

[0028] If the characteristic impedance of the capacitor-loaded transmission line cannot be adjusted to Z ANT Nearby, a capacitively loaded transmission line can be used as part of the LNA input matching circuit.

[0029] It should also be noted that the resistors, inductors, and capacitors mentioned above do not refer to a specific electronic device, but can also be resistors, inductors, and capacitors that are equivalent to circuits built in parallel, series, or other ways.

[0030] The RF front-end structure based on coupled lines of the present invention is independent of frequency and process. Theoretically, it can be implemented based on any process, such as GaAs, GaN, CMOS, etc., and can also be designed at any frequency. The implemented solution can be in the form of a monolithic integrated circuit (MMIC), that is, all components are on the same die, or a hybrid integrated circuit, that is, components are distributed on different dies or even PCB boards.

[0031] Compared with the traditional RF front end, the RF front end structure based on coupled lines proposed in the present invention has obvious advantages. First, by removing the transmitting switch, the transmission loss is reduced, which can significantly improve the transmission efficiency. Secondly, the coupled line balun can fully absorb the parasitic parameters of the transistor and provide an impedance transformation function, so the use of an additional PA output network can be avoided, which helps to further improve the PA efficiency. Finally, the coupled line has the advantages of broadband, low loss, and compact size, which can improve the overall performance of the RF front end.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A radio frequency front end based on a coupled line, comprising a transmitting branch and a receiving branch, characterized in that: The transmitting branch includes a differential power amplifier, a first coupling line and a second coupling line, the differential power amplifier includes a first transistor and a second transistor, the output end of the first transistor is connected to the first coupling line, the output end of the second transistor is connected to the second coupling line, the first coupling line is connected to an antenna, and the first coupling line and the second coupling line are connected; the receiving branch includes a low noise amplifier and a transceiver switch, and the second coupling line is connected to the transceiver switch; The drains of the first transistor and the second transistor of the differential power amplifier are respectively connected to a parasitic capacitor, and the other end of the parasitic capacitor is grounded; the sources of the first transistor and the second transistor are both grounded; The first coupling line includes a first transmission line and a second transmission line coupled to each other, the drain of the first transistor is connected to the first transmission line, and the other end of the first transmission line is grounded; one end of the second transmission line is connected to the second coupling line, and the other end is connected to the antenna, and a load capacitor C is provided between the antenna and the second transmission line. L , the load capacitance C L The other end is grounded; The second coupling line includes a third transmission line and a fourth transmission line coupled to each other, the drain of the second transistor is connected to the third transmission line, and the other end of the third transmission line is grounded; one end of the fourth transmission line is connected to the second transmission line, and the other end is connected to the transceiver switch.

2. The radio frequency front end according to claim 1, characterized in that: The first transistor and the second transistor are field effect transistors or bipolar transistors.

3. The radio frequency front end according to claim 1, characterized in that: The transceiver switch includes a switch and a parasitic capacitor connected in parallel with the switch.

4. The radio frequency front end according to claim 1, characterized in that: The transceiver switch is connected to the input end of the low noise amplifier.

5. The radio frequency front end according to claim 1, characterized in that: The RF front end is configured such that, in the transmission mode, the transceiver switch is closed, the low noise amplifier is turned off, the output parasitic capacitance of the first coupling line, the second coupling line and the transistor in the differential power amplifier, and the load capacitance C L The coupled line balun is formed, and the antenna impedance is Z ANT The coupled line balun is converted into an optimal load impedance R for the first transistor and the second transistor. opt .

6. The radio frequency front end according to claim 1, characterized in that: The RF front end is configured such that, in the receiving mode, the transceiver switch is disconnected, the differential power amplifier is turned off, the output impedance of the first transistor and the second transistor is short-circuited, and the parasitic capacitance of the first coupling line, the second coupling line, the switch and the load capacitance C L Form a capacitor loaded transmission line.

7. The radio frequency front end according to claim 6, characterized in that: The output impedance of the first transistor and the second transistor is short-circuited by closing the drain voltage and increasing the gate voltage.

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