A flat group delay radio frequency transceiver

Abstract

The present invention is a flat group delay radio frequency transceiver, comprising: a transmitter and a receiver; the transmitter and the receiver are connected to a common antenna for transmission and reception through a duplexer; the receiver comprises a receiving limiter, a low noise amplifier, a down converter, and a receiving intermediate frequency filter; the transmitter comprises a transmitting intermediate frequency filter, an up converter, a radio frequency filter, and a power amplifier, and the receiving intermediate frequency filter and the transmitting intermediate frequency filter are intermediate frequency cross-coupling filters respectively; the intermediate frequency cross-coupling filter comprises: a filter body comprising at least two microstrip line resonators; a first cross-coupling circuit and a second cross-coupling circuit for realizing the reverse compensation function of group delay. Since the present invention adopts an intermediate frequency cross-coupling filter in the intermediate frequency channel, the non-compensated state, the maximum flat compensation turntable, and the interference compensation state of group delay can be realized as required.

Description

Technical Field

[0001] The invention relates to the field of microwave radio frequency technology, in particular to a flat group delay radio frequency transceiver. Background Art

[0002] High-speed data transmission is widely used in terrestrial mobile communications, satellite communications, and data links. In modern communication systems, the presence of a large number of nonlinear devices in the RF link causes amplitude distortion and group delay distortion, which leads to waveform deterioration, inter-symbol interference, and spectrum leakage in high-speed data transmission, resulting in modulation signal disorder, increased system bit error rate, and even communication failure in severe cases.

[0003] Group delay refers to the time required for a complex signal or wave group composed of many spectral components with very close frequencies to pass through the network in a certain way. Since the responses of different frequency components in the signal are not exactly the same during transmission, the phase distortion of the signal can be measured by the group delay characteristics of the signal. Group delay represents the overall delay of a complex signal or wave group, not the phase delay of a certain frequency component in the complex signal or wave group, nor is it the average value of the phase delay of each frequency component in the complex signal or wave group. The group delay characteristics of the RF link are related to the phase response characteristics of the amplifiers, mixers, filters and other devices in the system. Devices such as amplifiers, mixers and multipliers have a relatively small impact on the group delay characteristics of the transceiver system, generally between tens of picoseconds and hundreds of picoseconds. Generally speaking, the group delay fluctuation of a link is mainly restricted by the filter in the link. Generally, the filter has a steep group delay fluctuation at the passband edge. If the signal is too close to the passband edge of the filter, the signal component of this frequency band will be delayed greatly. After passing through the filter, the signal of this frequency band will be difficult to combine with the signals of other frequency bands into a good waveform. This is the main reason for signal distortion, and the consequence is that the signal modulation domain deteriorates and the bit error rate increases.

[0004] The amplitude distortion of the signal link can be compensated by an amplitude equalizer, and the amplitude response of the channel can be leveled by pre-distortion or distortion compensation. There are two main ways to achieve flat group delay. One is to introduce opposite group delay fluctuations in the link to compensate for the original group delay. The other is to develop alternative devices with flat group delay for devices with large group delay fluctuations. The use of amplitude equalization networks or group delay equalization networks requires the introduction of additional devices, which increases the complexity of the circuit and reduces the reliability of the system. Therefore, it is hoped that devices with flat amplitude-frequency response and flat group delay will be developed to address the shortcomings of amplitude fluctuations and group delay fluctuations of existing devices, or to develop devices with amplitude-frequency response or reverse group delay with reverse change trends, in the hope of neutralizing the fluctuations in amplitude and group delay caused by other devices.

[0005] At present, the disadvantages of the above-mentioned prior art include:

[0006] The amplitude distortion of the link can be compensated by an amplitude equalizer, but the insertion of additional components increases the circuit complexity, difficulty and cost, and deteriorates the circuit reliability.

[0007] The method of introducing opposite group delay fluctuations to compensate for the original group delay also adds additional devices, resulting in increased circuit complexity, difficulty and cost, and reduced circuit reliability. Summary of the invention

[0008] In view of the shortcomings of the existing technology, the purpose of the present invention is to improve the group delay characteristics of the intermediate frequency filter without adding additional compensatory circuits and provide a flat group delay radio frequency transceiver.

[0009] The technical solution adopted by the present invention to achieve its technical purpose is: a flat group delay radio frequency transceiver, comprising: a transmitter and a receiver; the transmitter and the receiver are connected to a common antenna for transmission and reception through a duplexer; the receiver comprises a receiving limiter, a low noise amplifier, a down converter, and a receiving intermediate frequency filter; the radio frequency signal received by the common antenna for transmission and reception is successively passed through the receiving limiter, the low noise amplifier, the down converter, and the receiving intermediate frequency filter by the duplexer, and then a downlink intermediate frequency signal is output; the transmitter comprises a transmitting intermediate frequency filter, an up converter, a radio frequency filter, and a power amplifier, and the uplink intermediate frequency signal successively passes through the transmitting intermediate frequency filter, the up converter, the radio frequency filter, and the power amplifier to form a transmitting radio frequency signal, which is transmitted through the duplexer to the common antenna for transmission; the receiving intermediate frequency filter and the transmitting intermediate frequency filter are respectively intermediate frequency cross-coupling filters; the intermediate frequency cross-coupling filter comprises: a filter body comprising at least two microstrip line resonators; a first cross-coupling circuit and a second cross-coupling circuit for realizing the reverse compensation function of group delay.

[0010] Furthermore, in the above-mentioned flat group delay radio frequency transceiver: the filter body includes 8 microstrip line resonators.

[0011] Furthermore, in the above-mentioned flat group delay RF transceiver: the first cross-coupling circuit and the second cross-coupling circuit both include a cross-coupling phase shift adjustment circuit, and the cross-coupling phase shift adjustment circuit includes a 3dB bridge, and the input and output cross-coupled with different microstrip line resonators are respectively connected to the two ports of the 3dB bridge, and the remaining two ports of the 3dB bridge are connected to the voltage control port and grounded through a varactor diode.

[0012] Furthermore, in the above-mentioned flat group delay radio frequency transceiver: the low noise amplifier and the power amplifier are respectively broadband low noise amplifiers with adjustable feedback phase; the broadband low noise amplifier includes a first complementary metal oxide field effect transistor and a second complementary metal oxide field effect transistor;

[0013] The first complementary metal oxide field effect transistor adopts a common source structure, wherein a first feedback loop is introduced between the drain and the gate, and the source is grounded; a first phase adjustment structure is added to the first feedback loop;

[0014] The second complementary metal oxide field effect transistor adopts a common gate structure, introduces a second feedback loop between the drain and the source; and adds a second phase adjustment structure in the second feedback loop;

[0015] The radio frequency signal to be amplified is input from the gate of the first complementary metal oxide field effect transistor, connected to the source of the second complementary metal oxide field effect transistor after passing through the drain of the first complementary metal oxide field effect transistor, and finally the amplified radio frequency signal is output from the drain of the second complementary metal oxide field effect transistor.

[0016] Furthermore, in the above-mentioned flat group delay radio frequency transceiver: the first feedback loop and the second feedback loop respectively include a phase shifter for delaying the output signal by a set phase and then feeding it back to the input end.

[0017] Furthermore, in the above-mentioned flat group delay RF transceiver: the phase shifter is a phase-adjustable phase shifter.

[0018] Furthermore, in the above-mentioned flat group delay RF transceiver: the first feedback loop and the second feedback loop respectively include a second 3dB bridge and a second varactor diode, the input end and the output end of the first feedback loop or the second feedback loop are respectively connected to the two ports of the second 3db bridge, and the remaining two ports of the second 3db bridge are respectively grounded through the second varactor diode; and also includes a DAC, and the DAC generates a suitable DC voltage to adjust the junction capacitance of the second varactor diode.

[0019] Since the invention adopts an intermediate frequency cross-coupling filter in the intermediate frequency channel, the non-compensation state of group delay, the maximum flat compensation turntable and the interference compensation state can be realized as required.

[0020] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Attached Figure 1 This is a block diagram of a Ku-band flat group delay radio frequency transceiver according to an embodiment of the present invention;

[0022] Attached Figure 2 is a circuit diagram of an intermediate frequency filter with adjustable group delay in an embodiment of the present invention;

[0023] Attached Figure 3 A specific structural diagram of an intermediate frequency filter in an embodiment of the present invention;

[0024] Attached Figure 4 A cross-coupled phase shift adjustment circuit diagram in an intermediate frequency filter in an embodiment of the present invention;

[0025] Attached Figure 5 This is a diagram showing the delay adjustment effect of the intermediate frequency filter group in an embodiment of the present invention.

[0026] Attached Figure 6 This is a block diagram of a Ku-band low noise amplifier in an embodiment of the present invention;

[0027] Attached Figure 7 Detailed circuit diagram of the Ku-band low noise amplifier in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Embodiment 1, as Figure 1 As shown, this embodiment is a flat group delay radio frequency transceiver, and such a flat group delay radio frequency transceiver can be used to form a flat delay multi-path radar transceiver. Figure 1 As shown, the transceiver includes: a transmitter and a receiver; the transmitter and the receiver receive and transmit via a duplexer 2 and share a common antenna 1;

[0029] The receiver includes a receiving limiter 3, a low noise amplifier 4, a down converter 5, and a receiving intermediate frequency filter 6; the radio frequency signal (radar signal) received by the transmitting and receiving common antenna 1 passes through the duplexer 2 in turn through the receiving limiter 3, the low noise amplifier 4, the down converter 5, and the receiving intermediate frequency filter 6, and then outputs a downlink intermediate frequency signal IF_DN.

[0030] The transmitter includes a transmitting intermediate frequency filter 9, an up converter 10, a radio frequency filter 8 and a power amplifier 7. The uplink intermediate frequency signal IF_UP passes through the transmitting intermediate frequency filter 9, the up converter 10, the radio frequency filter 8 and the power amplifier 7 in sequence to form a transmitting radio frequency signal, which is then connected to the transmitting and receiving shared antenna 1 via the duplexer 2.

[0031] Microwave communication has the advantages of large communication capacity, wide coverage, good confidentiality, flexibility, stable and reliable performance, etc. Microwave (RF) transceivers are the core components of microwave communication and radar systems. Typical RF transceivers use superheterodyne frequency conversion structures. The role of the transmitter is to up-convert the intermediate frequency (or baseband) signal to the microwave band and then transmit it, and the function of the receiver is to receive the RF signal and then down-convert it to the intermediate frequency or baseband signal. In the frequency domain, the RF transmitter moves the spectrum of the intermediate frequency or baseband signal upward to the high frequency band, while the receiver moves the high frequency band downward back to the intermediate frequency or baseband. In order to ensure that the intermediate frequency signal still has a high signal quality after RF transceiver (can restore the initial transmission baseband information without loss or with low loss), the RF transceiver is required to have good transmission characteristics. In the frequency domain, the RF transceiver is required to have a flat amplitude characteristic within the communication bandwidth, and in the time domain, the RF transceiver is required to have a flat group delay within the communication bandwidth.

[0032] In this embodiment, a typical Ku-band radio frequency transceiver link is as follows: Figure 1 As shown, the transceiver shares antenna 1, and the transmitter and receiver are connected through a duplexer 2. The receiver includes modules such as a receiving limiter 3, a low noise amplifier 4, a down converter 5, and a receiving intermediate frequency filter 6, and the transmitter includes modules such as a transmitting intermediate frequency filter 9, an up converter 10, a radio frequency filter 8, and a power amplifier 7. In order to take into account both the performance and cost of the radio frequency link, the bandwidth of the filter (and duplexer) in the radio frequency band can be appropriately relaxed by 50-100%. A wider filter bandwidth is conducive to reducing radio frequency losses. However, a wider radio frequency filter brings additional noise in proportion. In order to remove noise outside the useful signal band, a narrowband filter needs to be inserted at the transceiver intermediate frequency. The narrowband (only 20% larger than the useful signal bandwidth) filter can effectively suppress the noise level, reduce the broadband transmission noise of the transmitter, and also reduce the background noise of the receiver.

[0033] In the RF link, the filter plays the role of passing the in-band signal with low loss and suppressing the out-band signal. In addition to requiring certain amplitude-frequency filtering characteristics, the filters used in the RF link for broadband communication also require that the distortion of the transmitted signal does not exceed the allowable range. The distortion of the signal is described by the phase-frequency characteristics of the filter. A good and distortion-free RF channel (or RF device) has a linear phase characteristic, which is manifested as a flat group delay characteristic in the time domain.

[0034] The group delay of conventional filters is low in the center of the passband and large at the edge of the filter passband. In order to make the group delay fluctuation meet a certain range, in communication design, the communication bandwidth can only occupy 1 / 3 to 1 / 2 of the effective bandwidth of the filter. A considerable proportion of the filter bandwidth cannot be used due to excessive group delay. In order to make the most of the filter passband, the industry has developed a filter with flat group delay. By introducing cross-coupling and other means, the group delay of the filter has the maximum flatness characteristic, so that the available bandwidth of the filter reaches 2 / 3 of the passband bandwidth.

[0035] In this embodiment, the narrowband filter is the main reason for the group delay fluctuation of the RF link. The group delay distortion of the filter at the edge of the passband is the largest. If only the flat part of the group delay in the center of the filter passband is used, it will lead to waste of filter bandwidth, and the excess noise power will enter and cause the noise floor to rise. To solve this problem, the industry has developed a flat group delay filter based on cross-coupling. That is, through cross-coupling, signal transmission of multiple paths is introduced into the filter, and the reverse trend of the group delay of a certain path is used to compensate for the group delay of other paths, thereby achieving a flat group delay with the maximum bandwidth within the filter band. A well-designed cross-coupled filter can achieve a flat group delay bandwidth of 65-85% of the filter amplitude bandwidth, which is a significant improvement over the 50% group delay available bandwidth of conventional filters. The cross-coupling technology of the filter is relatively complex and costly, and it is generally not appropriate to use multiple cross-coupled filters in the RF link. A better strategy is to use only one cross-coupled filter in the link, while the other filters are conventional filters. It is hoped that the cross-coupled filter has a reverse group delay compensation function, or the cross-coupled filter has a group delay adjustment function, which can be adjusted in real time according to the group delay characteristics of other devices in the link, thereby achieving a flat group delay characteristic of the entire link.

[0036] In this embodiment, the RF filter and duplexer use conventional filters. In order to reduce the loss of the RF front end, the filter bandwidth is relatively wide, and the signal spectrum is as close to the bandwidth center of the RF filter as possible. In this embodiment, the receiving IF filter and the transmitting IF filter are IF cross-coupling filters respectively; the IF cross-coupling filter includes: a filter body including 8 microstrip line resonators; a first cross-coupling circuit 41 and a second cross-coupling circuit 42 for realizing the reverse compensation function of group delay. The cross-coupling filter is applied to the IF, and one is used for each of the receiving link and the transmitting link. The structure of the filter is as follows: Figure 2 The intermediate frequency cross-coupling filter is mainly divided into three parts, namely the filter body (including 8 microstrip line resonators), the first cross-coupling circuit 41 and the second cross-coupling circuit 42. The two cross-coupling circuits are used to realize the reverse compensation function of the group delay. In this embodiment, the cross-coupling circuit adopts a phase shifter design as shown in FIG. Figure 4The cross-coupled phase-shifting adjustment circuit includes a 3dB bridge 424, the input and output of the cross-coupled microstrip line resonators are respectively connected to two ports of the 3dB bridge 424, and the remaining two ports of the 3dB bridge are connected to the voltage control port and grounded through a varactor diode.

[0037] The details of the cross-coupled filter are as follows Figure 3 As shown, the input and output of the cross-coupling are respectively connected to two ports of the 3dB bridge 424, and the remaining two ports of the 3dB bridge 424 are connected to the varactor diode. The phase adjustment of the phase shifter can be realized by the external control voltage, thereby changing the phase of the coupled signal of the filter cross-path, thereby realizing the adjustment of the filter group delay. The input / output port 401 of the filter is respectively arranged at both ends of the filter body 40 including 8 microstrip line resonators 402, and the two cross-coupling ends 421 and 422 of the first cross-coupling circuit 41 or the second cross-coupling circuit 42 are respectively connected to the microstrip line resonator 402, and the control voltage 423 on the voltage-controlled varactor diode 425 is respectively provided by the radar control system. Here, the two cross-coupling ends 421 and 422 are coupled through space, that is, the placement of two flat wires, and there is a certain electrical connection between the two, which is similar to the coupling connection between the input / output ports 401 and 402 of the filter body 40 and the input and output ends. In addition, the number of microstrip line resonators 402 in the filter body 40 can be adjusted according to practice. When the number of microstrip line resonators 402 changes, the positions of the two cross-coupling ends 421 and 422 will change. The positions of the two are not necessarily symmetrical. As for how they change, those skilled in the art can find out through calculation and simulation.

[0038] The intermediate frequency filter shown in the present invention has a group delay adjustment function, and can realize the group delay non-compensation state, the maximum flat compensation stage and the interference compensation state according to the needs. Among them, the interference compensation can compensate for the group delay fluctuation of other conventional filters. A radio frequency link can achieve the group delay flatness of the entire link by using an intermediate frequency filter based on cross-coupling, which has a high cost performance.

[0039] like Figure 5 As shown in FIG. 1 , the group delay adjustment effect of the frequency filter in this embodiment is shown in FIG. Figure 5 As shown, the curve indicated by 100 represents the curve without compensation, 200 represents the curve with flat compensation, and 300 represents the interference compensation curve.

[0040] In this embodiment, the low noise amplifier and the power amplifier are respectively broadband low noise amplifiers with adjustable feedback phase; the broadband low noise amplifier includes a first complementary metal oxide field effect transistor M1 and a second complementary metal oxide field effect transistor M2; the first complementary metal oxide field effect transistor M1 adopts a common source structure, in which a first feedback loop is introduced between the drain and the gate, and the source is grounded; a first phase adjustment structure is added to the first feedback loop.

[0041] The second complementary metal oxide field effect transistor M2 adopts a common gate structure, and introduces a second feedback loop between the drain and the source; and adds a second phase adjustment structure in the second feedback loop.

[0042] The RF signal to be amplified is input from the gate of the first complementary metal oxide field effect transistor M1, connected to the source of the second complementary metal oxide field effect transistor M2 after passing through the drain of the first complementary metal oxide field effect transistor M1, and finally the amplified RF signal is output from the drain of the second complementary metal oxide field effect transistor M2.

[0043] The first feedback loop and the second feedback loop respectively include a phase shifter for delaying the output signal by a set phase and then feeding it back to the input end. The phase shifter is a phase-adjustable phase shifter.

[0044] The first feedback loop and the second feedback loop respectively include a second 3dB bridge and a second varactor diode, the input end and the output end of the first feedback loop or the second feedback loop are respectively connected to the two ports of the second 3db bridge, and the remaining two ports of the second 3db bridge are respectively grounded through the second varactor diode; and also include a DAC, the DAC generates a suitable DC voltage to adjust the junction capacitance of the second varactor diode.

[0045] In microwave communication systems, broadband low-noise amplifiers play an important role and have a significant impact on the performance indicators of the entire system. Broadband low-noise amplifiers receive and amplify small signals with a very wide frequency band, and require low noise figures, high flatness of gain, good broadband input and output matching, good power linearity, and good phase linearity. In orthogonal frequency division multiplexing systems, in order to avoid mutual interference between adjacent channels, the amplitude linearity and phase linearity of the amplifier must meet certain indicators.

[0046] In response to the requirements for flat amplitude response and flat group delay characteristics of a broadband low-noise amplifier, in this embodiment, an extremely small low-noise amplifier based on a common source and common gate inverse structure operating in the 12.5-15 GHz frequency band is proposed. The amplifier uses two Ku-band complementary metal oxide field effect transistors (CMOS). The first field effect transistor adopts a common source structure, in which negative feedback is introduced between the drain and the gate to improve the stability of the amplifier. At the same time, a phase adjustment structure is added to the feedback circuit to adjust the amplifier amplitude curve and phase (group delay) curve. The second field effect transistor adopts a common gate structure, in which a feedback loop is introduced between the drain and the source to achieve the gain flatness of the amplifier. At the same time, a phase adjustment mechanism is introduced in the feedback loop to adjust the amplifier amplitude and phase. The principle block diagram of the broadband low-noise amplifier is shown in the figure. Figure 6 As shown, T1 and T3 are transmission lines of a certain electrical length, which are used to delay the output signal by a certain phase and then feed it back to the input end, that is, T1 and T3 are equivalent to phase shifters. If T1 and T3 have adjustable phase functions, the feedback adjustment function can be realized, thereby realizing the adjustment of the amplitude response and phase response of the amplifier.

[0047] Wideband low noise amplifier circuit with adjustable feedback phase such as Figure 7 As shown, the transmission lines T1 and T3 are realized by the cooperation of the second 3dB bridge and the varactor diode. The DC voltage V1 is used to adjust the junction capacitance of the varactor diode. Different junction capacitances will produce different phase shift effects on the input and output ends of the 3dB bridge, thereby realizing the adjustable feedback signal of the amplifier. When the amplifier is in use, the internal control circuit generates a suitable DC voltage through the DAC as required to drive the phase shifter to produce the required phase shift. The application of the phase shift feedback loop can achieve the amplifier gain flatness and group delay flatness.

Claims

1. A flat group delay radio frequency transceiver, comprising: Transmitters and receivers; The transmitter and the receiver share a common antenna for transmission and reception via a duplexer; The receiver includes a receiving limiter, a low noise amplifier, a down converter, and a receiving intermediate frequency filter; The radio frequency signal received by the transmit-receive shared antenna passes through the duplexer in sequence through a receiving limiter, a low noise amplifier, a down converter, and a receiving intermediate frequency filter, and then outputs a downlink intermediate frequency signal; the transmitter includes a transmitting intermediate frequency filter, an up converter, an radio frequency filter, and a power amplifier, and the uplink intermediate frequency signal passes through the transmitting intermediate frequency filter, the up converter, the radio frequency filter, and the power amplifier in sequence to form a transmitting radio frequency signal, which is then transmitted through the duplexer connected to the transmit-receive shared antenna; it is characterized in that: the receiving intermediate frequency filter and the transmitting intermediate frequency filter are intermediate frequency cross-coupling filters respectively; the intermediate frequency cross-coupling filter includes: a filter body including at least two microstrip line resonators; a first cross-coupling circuit and a second cross-coupling circuit for realizing the reverse compensation function of group delay; The filter body comprises 8 microstrip line resonators; The first cross-coupling circuit and the second cross-coupling circuit both include a cross-coupling phase-shifting adjustment circuit, which includes a 3dB bridge, wherein the input and output cross-coupled with different microstrip line resonators are respectively connected to two ports of the 3dB bridge, and the remaining two ports of the 3dB bridge are connected to the voltage control port and grounded through a varactor diode.

2. The flat group delay radio frequency transceiver according to claim 1, characterized in that: The low noise amplifier and the power amplifier are broadband low noise amplifiers with adjustable feedback phases; the broadband low noise amplifier comprises a first complementary metal oxide field effect transistor and a second complementary metal oxide field effect transistor; the first complementary metal oxide field effect transistor adopts a common source structure, wherein a first feedback loop is introduced between the drain and the gate, and the source is grounded; A first phase adjustment structure is added to the first feedback loop; the second complementary metal oxide field effect transistor adopts a common gate structure, and a second feedback loop is introduced between the drain and the source; a second phase adjustment structure is added to the second feedback loop; The radio frequency signal to be amplified is input from the gate of the first complementary metal oxide field effect transistor, connected to the source of the second complementary metal oxide field effect transistor after passing through the drain of the first complementary metal oxide field effect transistor, and finally the amplified radio frequency signal is output from the drain of the second complementary metal oxide field effect transistor.

3. The flat group delay radio frequency transceiver according to claim 2, characterized in that: The first feedback loop and the second feedback loop respectively include a phase shifter for delaying the output signal by a set phase and then feeding it back to the input end.

4. The flat group delay radio frequency transceiver according to claim 3, characterized in that: The phase shifter is a phase-adjustable phase shifter.

5. The flat group delay radio frequency transceiver according to claim 2, characterized in that: The first feedback loop and the second feedback loop respectively include a second 3dB bridge and a second varactor diode, the input end and the output end of the first feedback loop or the second feedback loop are respectively connected to the two ports of the second 3db bridge, and the remaining two ports of the second 3db bridge are respectively grounded through the second varactor diode; and also include a DAC, the DAC generates a suitable DC voltage to adjust the junction capacitance of the second varactor diode.

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