CN115580316B - Radio frequency front-end circuit and circuit board for 5G NR-U frequency band - Google Patents

Abstract

The invention discloses a communication circuit for a 5G NR-U frequency band, which comprises: the system comprises a radio frequency balun, a downlink radio frequency communication module and an uplink radio frequency communication module; the radio frequency balun is used for converting impedance matching between a differential balanced end signal and a single-ended signal output by the receiving radio frequency transceiver to generate an impedance matching signal; the downlink radio frequency communication module is used for carrying out power detection on the impedance matching signal based on the integrated circulator, the first radio frequency switch and the second radio frequency switch and outputting a gain radio frequency modulation signal; and the uplink radio frequency communication module is used for suppressing the received out-of-band signal and amplifying the in-band signal based on the integrated circulator and the second radio frequency switch to generate an amplified signal and sending the amplified signal to the radio frequency balun. The circuit provided by the invention can reduce the cost, is beneficial to the miniaturization of the circuit and meets the communication requirement of a 5G NR-U frequency band.

Description

A radio frequency front-end circuit and circuit board for 5G NR-U frequency band

technical field

The present invention relates to the field of wireless transmission technology, in particular to a radio frequency front-end circuit and circuit board for 5G NR-U frequency band.

Background technique

In the 5G wireless private network (professional network that provides safe and reliable wireless services for specific departments or groups, such as government affairs and public security industries), NR-U base stations, core network and other dedicated network equipment are independently deployed, which can greatly Business security, reliability, and specificity of the groups served. These specific groups are especially important for safety, such as substations and smart factories, and they can meet mobile and high-bandwidth business applications such as inspection robots in stations, mobile inspections, and video surveillance.

However, there are currently few base stations based on the 5G NR-U frequency band design in the market. Most of the base station radio frequency links use discrete devices. Mutual interference leads to deterioration of key radio frequency indicators (such as emission spurs, low receiving sensitivity, EVM, ACPR, etc.).

Contents of the invention

The technical problem to be solved by the present invention is to provide a radio frequency front-end circuit and circuit board for 5G NR-U frequency band, which can reduce costs, facilitate circuit miniaturization, and meet the communication requirements of 5G NR-U frequency band.

In order to solve the above technical problems, the first aspect of the present invention discloses a communication circuit for 5G NR-U frequency band, the communication circuit includes: radio frequency balun, downlink radio frequency communication module, uplink radio frequency communication module; radio frequency balun, It is used to convert the impedance matching between the differential balanced end signal and the single-ended signal output by the receiving radio frequency transceiver to generate an impedance matching signal; the downlink radio frequency communication module is used based on the integrated circulator, the first radio frequency switch and the second radio frequency The switch detects the power of the impedance matching signal and outputs a gain radio frequency modulation signal; the uplink radio frequency communication module is used to suppress the received out-of-band signal and perform signal amplification processing on the in-band signal based on the integrated circulator and the second radio frequency switch The amplified signal is generated and sent to the RF balun.

In some embodiments, the downlink radio frequency communication module includes: a signal amplification module, a coupler, a circulator, a first radio frequency switch, and a second radio frequency switch; The signal is coupled to generate a coupling signal; the circulator is used to receive the standing wave detection signal and the coupling signal for reading the antenna signal state to perform power detection and output the coupling signal of the gain; wherein, the circulator is respectively connected to the first radio frequency switch communicated with the second radio frequency switch.

In some implementations, wherein, both the first radio frequency switch and the second radio frequency switch are single-pole double-throw switches; the first end of the first radio frequency switch is connected to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver, the first The two ends are connected to the coupler, the third end is connected to the second radio frequency switch; the first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the first radio frequency switch; through the first radio frequency switch and the second The radio frequency switch implements the closed-loop control of the downlink.

In some embodiments, the signal amplification module includes: a driving stage power amplifier, a matcher and a final stage power amplifier.

In some embodiments, a pre-push stage power amplifier is further arranged between the push stage power amplifier and the radio frequency balun.

In some embodiments, the uplink radio frequency communication module includes: a low-noise amplifier, a low-pass filter, a circulator, and a second radio frequency switch; the circulator is used to receive the out-of-band signal input by the antenna and send it to the second radio frequency switch; the first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the low-noise amplifier, which is used to send the out-of-band signal to the low-noise amplifier for suppression and amplify the in-band signal to generate an amplified signal; low The pass filter is connected with the low-noise amplifier, and is used for low-pass filtering the amplified signal and outputting it to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver.

In some embodiments, the low-noise amplifier is an integrated two-stage low-noise amplifier; the low-pass filter is used to process the amplified signal generated by the integrated two-stage low-noise amplifier to carry out second and third harmonic out-of-band After the signal is suppressed and filtered, it is output to the RF balun on the feedback channel of the receiving RF transceiver.

In some embodiments, it further includes: a waveguide filter, used for suppressing emission spurs on the coupled signal output by the downlink radio frequency communication module or performing out-of-band blocking suppression on the out-of-band signal received by the uplink radio frequency communication module.

In some implementations, the communication circuit for the 5G NR-U frequency band implements signal processing of the downlink radio frequency communication module or the uplink radio frequency communication module through time division duplex mode.

According to the second aspect of the present invention, a communication circuit board for 5G NR-U frequency band is provided, including: a digital integrated circuit chip, a clock chip, a radio frequency transceiver, and a communication circuit board for 5G NR-U frequency band as described above. circuit; wherein, the radio frequency transceiver is connected to the communication circuit for 5G NR-U frequency band; the digital integrated circuit chip is respectively connected to the clock chip and the radio frequency transceiver; through the 5G The communication circuit in the NR-U frequency band controls the communication circuit board used in the 5G NR-U frequency band to achieve a working frequency band of 5.7GHz-5.9GHz.

Compared with prior art, the beneficial effect of the present invention is:

The implementation of the present invention can realize communication in the 5G NR-U frequency band through a highly integrated and miniaturized circuit controlled by a closed-loop control composed of a power amplifier, a first radio frequency switch, a second radio frequency switch, a circulator, a low noise amplifier, a coupler, etc. , and the total price is cheap, saving PCB size. In addition, the control of the first RF switch and the second RF switch ensures a high-quality output signal and reduces the variation of key RF indicators (such as emission spurs, low receiving sensitivity, EVM, ACPR) caused by wiring on the printed board. Difference. Moreover, the use of waveguide filters can control the signal insertion loss below 1dB, effectively suppress the adjacent WiFi frequency bands, reduce the interference with WiFi signals, and reduce the price and size at the same time.

Description of drawings

Fig. 1 is a schematic diagram of a circuit for communication in the 5G NR-U frequency band disclosed by an embodiment of the present invention;

Fig. 2 is a schematic diagram of another circuit for communication in the 5G NR-U frequency band disclosed by the embodiment of the present invention;

3 is a schematic diagram of an uplink circuit for communication in the 5G NR-U frequency band disclosed by an embodiment of the present invention;

4 is a schematic diagram of a downlink circuit for communication in the 5G NR-U frequency band disclosed by an embodiment of the present invention;

Fig. 5 is a schematic diagram of a communication circuit board for 5G NR-U frequency band for a specific application disclosed in an embodiment of the present invention;

Fig. 6 is a schematic diagram of a time synchronization signal of a communication circuit board used in the 5G NR-U frequency band for a specific application disclosed in the embodiment of the present invention.

Detailed ways

For better understanding and implementation, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention. rather than all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The terms "comprising" and "having" and any variations thereof in the embodiments of the present invention are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or modules is not necessarily limited to expressly Instead, other steps or modules not explicitly listed or inherent to the process, method, product or apparatus may be included.

The embodiment of the present invention discloses a communication circuit and circuit board for 5G NR-U frequency band, which can pass through a power amplifier, a first radio frequency switch, a second radio frequency switch, a circulator, a low noise amplifier, a coupler, etc. The closed-loop control composed of highly integrated and miniaturized circuits realizes communication in the 5G NR-U frequency band, and the overall price is cheap, saving PCB size. In addition, the control of the first RF switch and the second RF switch ensures a high-quality output signal and reduces the variation of key RF indicators (such as emission spurs, low receiving sensitivity, EVM, ACPR) caused by wiring on the printed board. Difference. Moreover, the use of waveguide filters can control the signal insertion loss below 1dB, effectively suppress the adjacent WiFi frequency bands, reduce the interference with WiFi signals, and reduce the price and size at the same time.

Please refer to Figure 1. Figure 1 is a schematic diagram of a communication circuit for 5G NR-U frequency band disclosed by an embodiment of the present invention. Wherein, the communication circuit for the 5G NR-U frequency band can be applied in the 5G communication system, and this embodiment of the present invention is not limited. As shown in Figure 1, the communication circuit for 5G NR-U frequency band: includes: radio frequency balun 1, downlink radio frequency communication module 2, and uplink radio frequency communication module 3.

RF Balun 1, also known as BALUN, is used to convert the impedance matching between the differential balanced end signal output by the receiving RF transceiver and the single-ended signal to generate an impedance matching signal. In the actual signal processing process, the receiving RF transceiver can be realized Impedance matching conversion between the 100 ohm or 50 ohm differential balanced end signal (phase difference 180°) of the machine Tranceiver and the RF 50 ohm single-ended signal. Afterwards, during the downlink processing, the radio frequency balun 1 sends the impedance matching signal to the downlink radio frequency communication module 2 .

The downlink radio frequency communication module 2 is configured to perform power detection on the impedance matching signal based on the integrated circulator, the first radio frequency switch and the second radio frequency switch, and output a radio frequency modulated signal of gain. The uplink radio frequency communication module 3 is used to suppress the received out-of-band signal and amplify the in-band signal based on the integrated circulator and the second radio frequency switch to generate an amplified signal and send it to the radio frequency balun 1 .

In other embodiments, as shown in Figure 2, the communication circuit for 5G NR-U frequency band also includes a waveguide filter 4, which is used to suppress the emission of the coupled signal of the gain output by the downlink radio frequency communication module or to suppress the uplink Out-of-band blocking suppression is performed on out-of-band signals received by the radio frequency communication module. Because for the filter of the antenna port, it is generally used for transmitting spurious suppression and receiving out-of-band blocking suppression, and is used to improve the receiver out-of-band blocking index. At present, most radio frequency circuits use cavity filters and dielectric filters. The insertion loss of cavity filters is slightly better than that of dielectrics, but they are generally customized, so the price will be very expensive and the size will be large. For the dielectric filter, not only the size is large, but also the insertion loss is very large, which will cause a high bit error rate. Since the working frequency band in the 5G NR-U system is 5.7-5.9GHz, according to the demand index, a waveguide filter is used in this embodiment, so that the insertion loss can be less than 1dB or even 0.6dB, and the The adjacent WiFi frequency band can be effectively suppressed by 20dB, thereby reducing interference with WiFi signals, and it is cheap and small in size.

Specifically, as a preferred embodiment, the downlink radio frequency communication module 2 can specifically be implemented as the structure shown in Figure 3, the downlink radio frequency communication module includes, a signal amplification module, a coupler, a circulator, a first radio frequency switch and Second RF switch. Among them, the signal amplification module includes: a driving stage power amplifier, a matcher and a final stage power amplifier, wherein the matcher refers to matching the impedance (the amount of the circuit's ability to hinder the passage of current) through resistance, capacitance, inductance or equivalent properties, and also It is to realize that the vector impedance becomes the RF 50 ohm impedance.

The coupler is used to obtain the signal processed by the signal amplification module in real time and perform coupling to generate a coupled signal, which can be expressed as DPD_FB. In practical applications, DPD_FB is realized to obtain the amplified signal output by the final stage PA in real time through a 30dB coupler. The quality of the DPD_FB signal is the same as that of the final PA, except that the signal amplitude is attenuated by 30dB. In this way, the channel for receiving the DPD_FB signal is connected through the second RF switch described below, and the signal can be fed back to the RF transceiver Tranceiver, so that the power can be read Or perform digital predistortion on the FPGA to meet the EVM (error vector magnitude) and ACLR (adjacent channel power ratio of radio frequency signals) indicators of the downlink indicators. The implementation of the line connection of the coupler in this embodiment is described in detail: the main function of the coupler is to output at the coupling end according to the size and quality of the direct connection signal, but the power amplifiers connected to the left and right ends of the coupler in this embodiment And the circulator, the path between the signal flow to the power amplifier-coupler-circulator uses the direct connection function of the coupler, and the coupling function is not used here. The signal flow direction is circulator—the path between the couplers uses the coupling function of the coupler, that is, the coupling signal is generated. The coupling signal is generated through the electromagnetic field coupling of the RF wiring inside the device, and does not involve physical electrical appliances. file connection.

The circulator is used to receive the standing wave detection signal for reading the signal state of the antenna, which can be expressed as VSWR_FB and the coupling signal for power detection and output a gain coupling signal. Among them, VSWR_FB is used to read the antenna signal status. When the device is processing downlink communication, the antenna matching status (open circuit, short circuit, load) can be detected by opening the connection between the VSWR_FB signal and the second RF switch. Because, at present, the output of the transmission signal state detection of the antenna port is generally output by power analog voltage, that is, in the final power amplifier (that is, the final PA shown in the figure) in the signal amplification module of the downlink radio frequency communication module. output. And for the 5.8G frequency band targeted by the present invention. WiFi and 5G NR-U have different definitions of ACPR (adjacent channel power ratio of radio frequency signals). Most of WiFi does not need to be canceled by external DPD (digital pre-distortion), which will lead to ACPR and The EVM (Error Vector Magnitude) is poor, resulting in a high bit error rate of data transmitted by the downlink antenna port, and causing interference to devices in adjacent frequency bands. This is also the defect of WiFi communication. Therefore, in this embodiment, the way of power detection and output coupling signal is adopted, so the downlink radio frequency communication module is integrated into this kind of circuit structure. In practical applications, by detecting the size of the output signal of the receiving end of the circulator and reading the standing wave detection signal of the antenna signal state, the state of the antenna port can be judged based on the required power detection algorithm. The state of the antenna port is, for example, You can apply for mismatch (short circuit, open circuit) and load matching. If a mismatch is detected, an alarm command of a standing wave detection signal will be sent to enter the logic process of antenna mismatch. The logic process is intelligently set according to experience, for example, the downlink data output can be turned off, and the signal quality of the receiving link can be detected. Fault location, etc., so that the power amplifier will not be burned out due to mismatch. The implementation of the line connection of the circulator in this embodiment is described in detail: in the actual line connection, the pin connected to the circulator and the coupler is defined as pin 1, and the pin connected to the waveguide filter is defined as pin 2 , the pin connected with the second radio frequency switch is defined as pin 3. Mainly explain the one-way communication function of the circulator in this embodiment. When pin 1 and pin 2 are connected, the signal flow can only flow from pin 1 to pin 2, but not from pin 2 to pin 1, which corresponds to the downlink In the road, the signal flow direction of the coupler to the waveguide filter can only be one-way, and the signal cannot be fed back, thus preventing the power amplifier from being burned by excessive signal power. Similarly, the signal flow can only flow from pin 2 to pin 3, which means that in the downlink, the signal flow direction is pin 1-pin 2-3, so that the waveguide filter can be directly connected in the band. In the function of out-of-band suppression, the detection of the signal behind the 3-pin can be equivalent to the detection of the standing wave state signal of the antenna.

Further, the circulator communicates with the first radio frequency switch and the second radio frequency switch respectively. Both the first radio frequency switch and the second radio frequency switch are single pole double throw switches. The first end of the first radio frequency switch is connected to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver, the second end is connected to the coupler, and the third end is connected to the second radio frequency switch. The first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the first radio frequency switch; the downlink closed-loop control is realized through the first radio frequency switch and the second radio frequency switch.

In other preferred implementation manners, a pre-push stage power amplifier (not shown in the figure) is further arranged between the push stage power amplifier and the radio frequency balun. Therefore, when the circuit of this embodiment is put into practical application, the downlink BBU (baseband processing unit) or fronthaul card outputs -14dBfs signal, the FPGA does not perform any power compensation control, and the RF transceiver Tranceiver reserves 6dB attenuation As frequency compensation and temperature compensation, the gain of the RF front-end circuit is about 32-33dB. Through calculation, it is determined that the antenna port can only output 20.5dB at most, and the margin is very small. Therefore, a pre-promoter PA is added between this circuit and the connection of the radio frequency transceiver Tranceiver, and the internal PA of the radio frequency integrated chip is used with the promotion stage and the final stage. Therefore, the output power headroom can be guaranteed, thereby satisfying various application scenarios such as coverage.

In the downlink radio frequency communication module, when the power amplifier PA of the downlink is turned on (enabling the pre-push stage and the downlink channel of the integrated radio frequency chip), due to the non-linear distortion of the PA, the Tranceiver chip detects the signal output by the coupler and down-converts the frequency It is an intermediate frequency signal, compared with the output of the intermediate frequency, the DPD (digital pre-distortion) digital check is used to eliminate the nonlinear distortion of the PA, and then the out-of-band suppression is performed through the waveguide filter to ensure the high quality of the output signal, and at the same time detect the feedback The power signal strength realizes the open and closed loop calibration of the power, and the uniform quality index can be achieved after the RF index deviation is passed through the closed loop calibration.

Specifically, as a preferred embodiment, the uplink radio frequency communication module 3 can be implemented as the structure shown in Figure 4, the uplink radio frequency communication module includes a low-noise amplifier, a low-pass filter, a circulator and a second radio frequency switch .

The circulator is used to receive the out-of-band signal input by the antenna and send it to the second radio frequency switch. The first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the low-noise amplifier for sending the out-of-band signal to the low-noise amplifier for signal amplification processing to generate an amplified signal. The low-pass filter is connected with the low-noise amplifier, and is used for low-pass filtering the amplified signal and outputting it to the feedback of the receiving radio frequency transceiver. RF balun on channel.

In a preferred implementation manner, the low noise amplifier is an integrated two-stage low noise amplifier, which is specifically implemented as an amplifier with a noise figure of 0.5-1 dB. The low-pass filter is used to suppress and filter the out-of-band signal of the second and third harmonics of the amplified signal generated by the integrated two-stage low-noise amplifier, and then output it to the RF balun on the feedback channel of the receiving RF transceiver.

In the uplink RF communication module, the out-of-band signal enters the waveguide filter through the antenna port, and the waveguide filter suppresses the out-of-band signal to improve the out-of-band blocking index of the receiver, and then amplifies the input value through the low-noise amplifier LNA The low-pass filter is suppressed and filtered and then output to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver. The gain of the built-in LNA of the uplink can reach 16dB, so as to ensure that weak signals can be sampled when they enter the digital integrated chip FPGA, and will not be submerged and cannot be demodulated.

It should be noted that the whole circuit adopts the TDD (time division duplex) mode, and the LNA amplification enablement, standing wave signal, DPD signal, downlink PA enablement, etc. can all be controlled by one IO pin. If it is a discrete device using the existing technology, it needs multiple IO pins to enable control. If the board level interference is large, there will be asynchronous arrival of the signals of each control pin, which will easily cause inconsistent timing of sending and receiving, and at least the data cannot be communicated. , the system radio frequency link is short-circuited, and the whole machine is short-circuited. To a certain extent, it has higher reliability and strong environmental adaptability.

Please refer to Figure 5, which is a schematic diagram of a communication circuit board for 5G NR-U frequency band disclosed by an embodiment of the present invention. Including: a digital integrated circuit chip FPGA, a clock chip PLL, a radio frequency transceiver Tranceiver chip, and a communication circuit for the 5G NR-U frequency band as described in the above embodiment; Communication circuit connection. The digital integrated circuit chip FPGA is connected to the clock chip PLL and the radio frequency transceiver Tranceiver respectively; the communication circuit board used for the 5G NR-U frequency band is controlled by the communication circuit for the 5G NR-U frequency band to realize the working frequency band of 5.7GHz-5.9GHz. By adopting the integrated structure of the field programmable logic gate array + Tranceiver chip in the digital integrated circuit chip, software programming can be performed on the FPGA according to the application scenario, and it has enough computing power for WiFi digital signal processing. The radio frequency part adopts a zero-IF solution, and the Tranceiver chip Support 650MHz-6000MHz frequency output, that is, the system hardware circuit can be compatible with WiFi circuit without any modification. The working frequency band of the entire circuit board is 5.7-5.9GHz of 5GNR-U, the signal bandwidth is NR-U 100MHz, 256QAM modulation, PAR (signal peak-to-average ratio) 8.5db, the total output power of 4T4R is not higher than 4W, and the radio frequency The front-end integration is high, the index is better, the cost and power consumption of the whole machine are greatly reduced, and the PCB size is reduced.

Further, as shown in FIG. 6 , in order to synchronize the input and output times of the entire circuit board. Firstly, the communication data of BBU or FH is encoded and decoded, compressed and decompressed, and data aggregated and distributed through the optical port. The 156.25M clock signal is recovered from the optical port data stream of the downlink BBU or FH, and the FPGA sends the recovered 156.25M clock to the PLL clock chip as a reference clock. After the clock chip detects the 156.25M reference clock, use it as a reference Lock and output a clock signal that is synchronized with the BBU and FH clocks, thereby ensuring the synchronization of the input and output time of the whole machine.

The above-described embodiments are only illustrative, and the modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical modules, that is, they may be located in a place, or can also be distributed to multiple network modules. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. It can be understood and implemented by those skilled in the art without any creative effort.

Through the specific description of the above embodiments, those skilled in the art can clearly understand that each implementation manner can be implemented by means of software plus a necessary general-purpose hardware platform, and of course also by hardware. Based on this understanding, the above-mentioned technical solution essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, and the storage medium includes a read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), programmable read-only memory (Programmable Read-only Memory, PROM), erasable programmable read-only memory (Erasable Programmable Read Only Memory, EPROM) , One-time Programmable Read-Only Memory (OTPROM), Electronically Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory , CD-ROM) or other optical disk storage, magnetic disk storage, tape storage, or any other computer-readable medium that can be used to carry or store data.

Finally, it should be noted that: a kind of communication circuit and circuit board for 5G NR-U frequency band disclosed in the embodiment of the present invention is only a preferred embodiment of the present invention, and is only used to illustrate the technology of the present invention scheme, rather than its limitation; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand; it can still modify the technical scheme described in the foregoing embodiments, or modify the Some technical features are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (10)

1. A communication circuit for 5G NR-U frequency band, characterized in that, the communication circuit includes: a radio frequency balun, a downlink radio frequency communication module, and an uplink radio frequency communication module; The RF balun is used to convert the impedance matching between the differential balanced end signal output by the receiving RF transceiver and the single-ended signal to generate an impedance matching signal; The downlink radio frequency communication module is used to perform power detection on the impedance matching signal based on the integrated circulator, the first radio frequency switch and the second radio frequency switch to output the radio frequency modulation signal of the gain; The uplink radio frequency communication module is used to suppress the received out-of-band signal and amplify the in-band signal based on the integrated circulator and the second radio frequency switch to generate an amplified signal and send it to the radio frequency balun. 2. The communication circuit for the 5G NR-U frequency band according to claim 1, wherein the downlink radio frequency communication module comprises: A signal amplification module, a coupler, a circulator, a first radio frequency switch and a second radio frequency switch; A coupler, used to obtain in real time the signal processed by the signal amplification module for coupling to generate a coupled signal; The circulator is used to receive the standing wave detection signal and the coupling signal for reading the signal state of the antenna, perform power detection and output the coupling signal of the gain; Wherein, the circulator communicates with the first radio frequency switch and the second radio frequency switch respectively. 3. The communication circuit for 5G NR-U frequency band according to claim 2, characterized in that, Wherein, the first radio frequency switch and the second radio frequency switch are single-pole double-throw switches; The first end of the first radio frequency switch is connected to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver, the second end is connected to the coupler, and the third end is connected to the second radio frequency switch; The first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the first radio frequency switch; The closed-loop control of downlink is realized by the first radio frequency switch and the second radio frequency switch. 4. The communication circuit for 5G NR-U frequency band according to claim 3, wherein the signal amplification module comprises: a push stage power amplifier, a matcher and a final stage power amplifier. 5. The communication circuit for 5G NR-U frequency band according to claim 4, characterized in that, a pre-push power amplifier is also arranged between the push stage power amplifier and the radio frequency balun. 6. The communication circuit for the 5G NR-U frequency band according to claim 1, wherein the uplink radio frequency communication module includes: low noise amplifier, low pass filter, circulator and second radio frequency switch; a circulator, configured to receive an out-of-band signal input by the antenna and send it to the second radio frequency switch; The first end of the second radio frequency switch is connected to the circulator, and the second end is connected to the low-noise amplifier, which is used to send the out-of-band signal to the low-noise amplifier for suppression and amplify the in-band signal to generate an amplified signal; The low-pass filter is connected to the low-noise amplifier, and is used to low-pass filter the amplified signal and output it to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver. 7. The communication circuit for 5G NR-U frequency band according to claim 6, characterized in that, The low noise amplifier is an integrated two-stage low noise amplifier; The low-pass filter is used to suppress and filter second and third harmonic out-of-band signals on the amplified signal generated by the integrated two-stage low-noise amplifier, and then output it to the radio frequency balun on the feedback channel of the receiving radio frequency transceiver. 8. The communication circuit for the 5G NR-U frequency band according to any one of claims 1-7, further comprising: The waveguide filter is used for suppressing transmission spurs on the gain coupled signal output by the downlink radio frequency communication module or performing out-of-band blocking suppression on the out-of-band signal received by the uplink radio frequency communication module. 9. The communication circuit for the 5G NR-U frequency band according to claim 8, wherein the communication circuit for the 5G NR-U frequency band realizes the downlink radio frequency communication module or the uplink radio frequency communication module through the time division duplex mode signal processing. 10. A communication circuit board for 5G NR-U frequency band, characterized in that, comprising: A digital integrated circuit chip, a clock chip, a radio frequency transceiver, and a communication circuit for the 5G NR-U frequency band as described in any one of claims 1-9; Wherein, the radio frequency transceiver is connected to the communication circuit for the 5G NR-U frequency band; The digital integrated circuit chip is respectively connected to the clock chip and the radio frequency transceiver; The communication circuit board used for the 5G NR-U frequency band is controlled by the communication circuit for the 5G NR-U frequency band to realize a working frequency band of 5.7GHz-5.9GHz.

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