TDD synchronization circuit, frequency conversion circuit and private network module

Abstract

This utility model relates to the field of private network communication, specifically a TDD synchronization circuit, a frequency conversion circuit, and a private network module, belonging to the technical field of private network communication. The TDD synchronization circuit includes a radio frequency detector, a high-speed comparator, and a NOT gate, used to demodulate the TDD synchronization signal from the radio frequency output signal of the public network module, without requiring the public network module itself to provide the signal. The frequency conversion circuit uses the TDD synchronization signal to control the switching of the radio frequency switch and converts the public network frequency band signal to the private network frequency band through up-converters and down-converters. The private network module integrates the above circuit. This utility model independently extracts the TDD synchronization signal through hardware circuitry, solving the dependence of existing technologies on the need for customized output synchronization signals from public network modules, and enabling the private network module to be compatible with public network modules from different manufacturers, improving the versatility and flexibility of the design, and reducing secondary development costs and time.

Description

Technical Field

[0001] This utility model relates to the field of private network communication technology, specifically to a TDD synchronization circuit, a frequency conversion circuit, and a private network module. Background Technology

[0002] There are two existing methods for implementing private network modules: one is the baseband + RF direct output mode, and the other is to operate in the private network frequency band through frequency conversion by the public network module. For TDD-type private network modules using frequency conversion, existing technology requires the public network module to output a TDD (Time Division Duplexing) transmit / receive synchronization signal to the private network module to control the transmit / receive switching of the module's frequency conversion circuit, in order to ensure the normal operation of the private network module.

[0003] For TDD-based private network modules using frequency conversion schemes, the following two problems exist: Public network modules require the output of TDD synchronization signals. Typical commercial public network terminal modules do not have TDD synchronization signal output and require software customization from public network module manufacturers.

[0004] If the public network module is replaced with one from a different manufacturer due to considerations such as cost and functionality, and if the TDD synchronization signal changes, the product circuit board will need to be redeveloped, increasing costs and time.

[0005] Therefore, there is an urgent need for a TDD synchronization solution that does not rely on public network modules to provide synchronization signals, in order to improve the independence and compatibility of private network module design. Utility Model Content

[0006] This utility model addresses the technical problems existing in the prior art by providing a TDD synchronization circuit, a frequency conversion circuit, and a private network module, thereby reducing reliance on public network modules and improving the versatility of private network equipment design.

[0007] In a first aspect, embodiments of the present invention provide a TDD synchronization circuit, comprising: Radio frequency detectors, high-speed comparators, and NOT gates; The input terminal of the radio frequency detector is used to couple to the coupling output terminal of the radio frequency coupler to receive the radio frequency coupling signal output by the public network module, and to detect the radio frequency coupling signal and output the modulation signal envelope. The first input terminal of the high-speed comparator is coupled to the output terminal of the radio frequency detector, and the second input terminal is coupled to the reference voltage. It is used to compare the modulation signal envelope with the reference voltage and output a first TDD synchronization signal. The input terminal of the NOT gate is coupled to the output terminal of the high-speed comparator, and is used to invert the first TDD synchronization signal and output the second TDD synchronization signal.

[0008] Furthermore, the radio frequency detector is configured to output a first voltage when the radio frequency coupled signal is in the transmission time domain and to output a second voltage when it is in the reception time domain; wherein the first voltage is greater than the second voltage.

[0009] Furthermore, the reference voltage is set to be between the first voltage and the second voltage.

[0010] The beneficial effects of this TDD synchronization circuit are as follows: An envelope detector is used to perform envelope detection on the radio frequency signal coupled from the public network module, obtaining an analog voltage reflecting the periodic changes in signal power. A high-speed comparator then compares this analog voltage with a set reference voltage to demodulate the digital signal (TX_EN) representing the transmission period. Finally, this digital signal (RX_EN) is obtained by inverting the signal through a NOT gate. These two signals together constitute the TDD synchronization signal required to control subsequent circuits. Its advantage lies in extracting synchronization information entirely from the radio frequency signal through hardware circuitry, eliminating the need for an additional synchronization signal output from the public network module, thus achieving decoupling from the public network module.

[0011] Secondly, this utility model embodiment provides a frequency conversion circuit, including: a TDD synchronization circuit as described in any one of claims 1-3; The first radio frequency switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal output by the TDD synchronization circuit, is used to separate the public network transmit and receive combined signal from the radio frequency coupler into a public network transmit signal and a public network receive signal. The second radio frequency switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal, is used to combine or separate the processed private network transmission signal from the private network reception signal from the antenna. Radio frequency local oscillator circuit, used to generate radio frequency local oscillator signal; The upconverter has its input terminal coupled to the public network transmission signal output terminal of the first RF switch and the output terminal of the RF local oscillator circuit, and is used to upconvert the public network transmission signal to the private network transmission frequency band. A power amplifier, with its input terminal coupled to the output terminal of the upconverter and its output terminal coupled to the second RF switch, is used to amplify the private network transmission signal after upconversion. A low-noise amplifier, with its input coupled to the second RF switch, is used to amplify the private network received signal from the antenna; The downconverter has its input terminal coupled to the output terminal of the low-noise amplifier and the output terminal of the RF local oscillator circuit, and its output terminal coupled to the first RF switch. It is used to downconvert the private network received signal to the public network received frequency band.

[0012] Furthermore, the radio frequency local oscillator circuit includes: a temperature-compensated crystal oscillator, a phase-locked loop, and a microcontroller; The output terminal of the temperature-compensated crystal oscillator is coupled to the reference clock input terminal of the phase-locked loop to provide a reference clock signal; The microcontroller communicates with the phase-locked loop (PLL) via a serial peripheral interface to configure and control the PLL to output the radio frequency local oscillator signal at a specified frequency.

[0013] Furthermore, the operating states of the first RF switch and the second RF switch are complementaryly controlled by the first TDD synchronization signal and the second TDD synchronization signal to achieve switching of the transceiver channel.

[0014] Furthermore, the enable terminal of the power amplifier and / or the enable terminal of the low-noise amplifier are coupled to the TDD synchronization circuit to control its activation or deactivation according to the first TDD synchronization signal and / or the second TDD synchronization signal.

[0015] The beneficial effects of this frequency conversion circuit are as follows: This circuit integrates the aforementioned TDD synchronization circuit and uses its output synchronization signal to control the switching of the entire transceiver link. Specifically, it includes: first and second RF switches controlled by the synchronization signal, used to separate / combine public network and private network signals; an RF local oscillator circuit, used to provide the local oscillation signal required for frequency conversion; an up-converter and a power amplifier, used to convert and amplify the public network transmission signal to the private network transmission frequency band; and a low-noise amplifier and a down-converter, used to amplify the private network reception signal and convert it back to the public network reception frequency band. Its beneficial effect lies in the fact that by using the independently extracted synchronization signal to precisely control the RF switches and amplifiers, stable and reliable transparent transmission of public network TDD signals to private network TDD signals is achieved. The entire circuit becomes an independent frequency conversion functional unit adaptable to different public network modules.

[0016] Thirdly, this utility model embodiment provides a private network module, including: a public network module, an RF coupler, an antenna interface, and a frequency conversion circuit; The RF output terminal of the public network module is coupled to the input terminal of the RF coupler; The direct output terminal of the RF coupler is coupled to the signal input terminal of the frequency conversion circuit, and its coupled output terminal is used to provide an RF coupling signal to the outside. The signal output / input terminal of the frequency conversion circuit is coupled to the antenna interface.

[0017] Furthermore, the input terminal of the TDD synchronization circuit in the frequency conversion circuit is externally coupled to the coupling output terminal of the radio frequency coupler to receive the radio frequency coupling signal.

[0018] Furthermore, the public network module operates in the TDD mobile communication frequency band.

[0019] The beneficial effects of this utility model's private network module are as follows: The module includes a public network module, an RF coupler, and the aforementioned frequency conversion circuit. The RF output of the public network module is split into two by the RF coupler: one path (direct-through) is sent to the frequency conversion circuit for frequency conversion; the other path (coupled) can be provided to an external or integrated TDD synchronization circuit for extracting synchronization signals. The private network signal processed by the frequency conversion circuit is connected to an external antenna through an antenna interface. Its advantages lie in forming a complete private network communication solution that does not rely on the synchronization signal output of a specific public network module, greatly improving the module's compatibility and portability, facilitating rapid product iteration, and reducing maintenance costs. Attached Figure Description

[0020] Figure 1 This is a schematic block diagram of the TDD synchronization circuit of this utility model; Figure 2 This is a block diagram illustrating the principle of the frequency conversion circuit of this utility model; Figure 3 This is a schematic diagram of the private network module of this utility model; Figure 4 This is a circuit diagram of the TDD synchronization circuit and frequency conversion circuit of this utility model; Figure 5 This is a TDD synchronization circuit diagram of this utility model; Figure 6 This is a first part of the transceiver link of the frequency conversion circuit of this utility model; Figure 7 This is the second part of the transceiver link of the frequency conversion circuit of this utility model; Figure 8 This is the third part of the transceiver link of the frequency conversion circuit of this utility model; Figure 9 This is a circuit diagram of the radio frequency local oscillator section of the frequency conversion circuit of this utility model. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this technology based on the specific circumstances.

[0024] In the description of this application, spatial relation terms such as "below," "under," "below," "below," "above," "over," etc., are used herein to describe the relationship between one element or feature shown in the figures and other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, an element or feature described as "below" or "under" or "below" of other elements or features will be oriented "above" other elements or features. Therefore, the exemplary terms "below" and "under" can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein are interpreted accordingly.

[0025] In the description of this application, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to implement and use the present invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the present invention can be implemented without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the present invention with unnecessary detail. Therefore, the present invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0026] Example 1 like Figure 1 and Figure 4 As shown, this embodiment of the present invention provides a TDD synchronization circuit, including: The input end of the radio frequency detector is configured to couple to the coupling output end of the radio frequency coupler, so as to receive the radio frequency coupled signal output by the public network module, detect the radio frequency coupled signal, and output a modulated signal envelope; output a first voltage when the radio frequency coupled signal is in a transmission time domain; output a second voltage when the radio frequency coupled signal is in a reception time domain; wherein the first voltage is greater than the second voltage.

[0027] The first input end of the high-speed comparator is coupled to the output end of the radio frequency detector, and the second input end is coupled to a reference voltage, configured to compare the modulated signal envelope with the reference voltage and output a first TDD synchronization signal; the reference voltage is set to be between the first voltage and the second voltage.

[0028] The input end of the NOT gate circuit is coupled to the output end of the high-speed comparator, configured to invert the first TDD synchronization signal and output a second TDD synchronization signal.

[0029] The TDD synchronization circuit is mainly composed of a radio frequency detector U100 (or a functionally equivalent detection circuit), a high-speed comparator, and a subsequent NOT gate (which may be integrated in a logic circuit in the figure). During operation, the TDD standard radio frequency signal (such as the 2600MHz signal in the N41 frequency band) output by the public network module (not fully shown in the figure) passes through the radio frequency coupler U101. The coupling end (COUP) of the radio frequency coupler U101 outputs a small part of radio frequency energy (signal N41_COUP) to the radio frequency detector U100. The radio frequency detector U100 performs envelope detection on the radio frequency signal. Since the power of the TDD signal in the transmission time slot is much greater than the power in the reception time slot, an analog voltage waveform with varying amplitude synchronized with the TDD period (such as 10ms) is generated at its output terminal VOUT. This waveform is a high voltage VOUT_TX in the transmission time domain, and a low voltage VOUT_RX in the reception time domain.

[0030] This analog voltage VOUT is sent to the non-inverting input end of the high-speed comparator, and the inverting input end of the comparator is connected to a carefully set reference voltage VREF. The value of VREF should be set between VOUT_TX and VOUT_RX. Therefore, when the signal is in the transmission time domain (VOUT_TX>VREF), the comparator outputs a high level (such as 3.3V); when the signal is in the reception time domain (VOUT_RX<VREF), the comparator outputs a low level (0V). In this way, the output of the comparator directly corresponds to the "transmission enable" signal TX_EN. The TX_EN signal then undergoes logical inversion through a NOT gate (or inverter) to obtain the "reception enable" signal RX_EN. TX_EN and RX_EN are a pair of complementary square wave signals whose period is synchronized with the public network TDD frame.

[0031] The circuit in this embodiment successfully extracts the TDD synchronization signal directly from the public network radio frequency signal, completely eliminating the dependence on the public network module hardware or software interface, and providing an independent timing control source for the subsequent frequency conversion circuit.

[0032] Example 2 like Figures 2 to 9 As shown, this utility model provides a frequency conversion circuit, including: the TDD synchronization circuit as described in Embodiment 1.

[0033] The first radio frequency switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal output by the TDD synchronization circuit, is used to separate the public network transmit / receive combined signal from the radio frequency coupler into a public network transmit signal and a public network receive signal.

[0034] The second RF switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal, is used to combine or separate the processed private network transmit signal from the private network receive signal from the antenna. The operating states of the first RF switch and the second RF switch are complementaryly controlled by the first TDD synchronization signal and the second TDD synchronization signal to achieve switching of the transmit and receive channels.

[0035] The radio frequency (RF) local oscillator circuit is used to generate an RF local oscillator signal. The RF local oscillator circuit includes a temperature-compensated crystal oscillator (TCC), a phase-locked loop (PLL), and a microcontroller. The output of the TCC is coupled to the reference clock input of the PLL to provide a reference clock signal. The microcontroller communicates with the PLL via a serial peripheral interface to configure and control the PLL to output the RF local oscillator signal at a specified frequency.

[0036] The upconverter has its input terminal coupled to the public network transmission signal output terminal of the first RF switch and the output terminal of the RF local oscillator circuit, and is used to upconvert the public network transmission signal to the private network transmission frequency band.

[0037] The power amplifier has its input terminal coupled to the output terminal of the up-converter and its output terminal coupled to the second RF switch, and is used to amplify the private network transmission signal after up-conversion; the enable terminal of the power amplifier and / or the enable terminal of the low-noise amplifier are coupled to the TDD synchronization circuit to control its opening or closing according to the first TDD synchronization signal and / or the second TDD synchronization signal.

[0038] A low-noise amplifier, with its input coupled to the second RF switch, is used to amplify the private network received signal from the antenna.

[0039] The downconverter has its input terminal coupled to the output terminal of the low-noise amplifier and the output terminal of the RF local oscillator circuit, and its output terminal coupled to the first RF switch. It is used to downconvert the private network received signal to the public network received frequency band.

[0040] The frequency conversion circuit receives the public network transmit / receive combined signal N41_TRX from the through-hole (ISO / DIR direction) of the RF coupler U101. The TDD synchronization signals TX_EN and RX_EN from Embodiment 1 control the first RF switch U204. When TX_EN is active (high level), switch U204 connects N41_TRX to the N41_TX path (public network transmission); when RX_EN is active (high level), it connects N41_TRX to the N41_RX path (public network reception), thereby achieving the separation of public network signal transmission and reception.

[0041] The RF local oscillator circuit consists of a microcontroller U302, a temperature-compensated crystal oscillator U301, and a phase-locked loop (PLL) U300. The temperature-compensated crystal oscillator U301 provides a stable 19.2MHz reference clock to the PLL U300. The microcontroller U302 configures the internal registers of the PLL U300 via the SPI bus (SPI_CLK, SPI_DO, SPI_CS) to control it to generate, for example, 3350MHz RF local oscillator signals TX_RF_LO and RX_RF_LO.

[0042] For the transmission link: the separated public network transmission signal N41_TX and the RF local oscillator TX_RF_LO are input together into the up-converter U202 for mixing to obtain the up-converted private network transmission signal (e.g., 2600M + 3350M = 5950M). This signal is amplified by the power amplifier U203 to become the private network transmission signal 5G95_TX. Under the control of the synchronization signal, the second RF switch (included in the link in the figure, controlling the combining) turns on 5G95_TX to the antenna port 5G95_ANT0 during the transmission time slot.

[0043] For the receiving link: The private network received signal 5G95_ANT0 from the antenna port is separated into 5G95_RX by the second RF switch in the receiving time slot. 5G95_RX is amplified by the low-noise amplifier U207 and then mixed with the RF local oscillator RX_RF_LO by the downconverter U200 to obtain the downconverted public network received signal N41_RX (e.g., 5950M-3350M=2600M). N41_RX is merged with the N41_TX path (where there is no signal when the transmitting link is disconnected) through the first RF switch U204 in the receiving time slot, restoring the public network transmit / receive combined signal N41_TRX, which is fed back to the RF coupler U101 and finally delivered to the public network module.

[0044] This frequency conversion circuit utilizes a self-extracted TDD synchronization signal as a global timing reference to coordinate and control multiple RF switches, power amplifiers, and low-noise amplifiers, achieving accurate and stable full-duplex frequency conversion between public and private network signals. The entire circuit operates as an independent unit, independent of any specific interface on the public network module.

[0045] Example 3 like Figure 3 As shown, this utility model provides a private network module, including: a public network module, an RF coupler, an antenna interface, and a frequency conversion circuit as described in Embodiment 2; the RF output terminal of the public network module is coupled to the input terminal of the RF coupler; the direct output terminal of the RF coupler is coupled to the signal input terminal of the frequency conversion circuit, and its coupled output terminal is used to provide an RF coupling signal to the outside; the signal output / input terminal of the frequency conversion circuit is coupled to the antenna interface.

[0046] The input terminal of the TDD synchronization circuit in the frequency conversion circuit is externally coupled to the coupling output terminal of the RF coupler to receive the RF coupling signal. The public network module operates in the TDD mobile communication frequency band.

[0047] This private network module integrates a public network module (e.g., a 5G module), an RF coupler U101, and the frequency conversion circuit described in Example 2 into the same hardware board or module. The RF output port of the public network module is connected to the input port of the RF coupler U101. The through output port of the RF coupler U101 is connected to the signal input port of the frequency conversion circuit (i.e., the input port of the first RF switch U204). The coupling output port of the RF coupler U101 can be directly connected to the TDD synchronization circuit integrated inside the frequency conversion circuit (as shown in Example 1), or a test point or connector can be provided for external debugging or connection to a separate synchronization circuit board. The final RF input / output port of the frequency conversion circuit (i.e., the private network antenna port 5G95_ANT0) is connected to an RF connector J200 for connecting an external private network antenna.

[0048] The private network module in this embodiment constitutes a complete communication terminal solution. Its greatest advantage lies in its "plug-and-play" compatibility: as long as the public network module can provide standard radio frequency signals, regardless of its model, manufacturer, or whether its internal software supports synchronous signal output, this private network module can operate in the specified private network frequency band through its built-in TDD synchronization circuit and frequency conversion circuit. This greatly simplifies product design, supply chain management, and subsequent upgrades and maintenance.

[0049] While embodiments or examples of this disclosure have been described with reference to the accompanying drawings, it should be understood that the above embodiments are merely exemplary embodiments or examples, and the scope of this utility model is not limited by these embodiments or examples, but only by the granted claims and their equivalents. Various elements in the embodiments or examples may be omitted or replaced by their equivalents. Furthermore, the steps may be performed in a different order than that described in this disclosure. Further, various elements in the embodiments or examples may be combined in various ways. Importantly, as the technology evolves, many elements described herein can be replaced by equivalents that appear after this disclosure.

Claims

1. A TDD synchronization circuit, characterized in that, include: Radio frequency detectors, high-speed comparators, and NOT gates; The input terminal of the radio frequency detector is used to couple to the coupling output terminal of the radio frequency coupler to receive the radio frequency coupling signal output by the public network module, and to detect the radio frequency coupling signal and output the modulation signal envelope. The first input terminal of the high-speed comparator is coupled to the output terminal of the radio frequency detector, and the second input terminal is coupled to the reference voltage. It is used to compare the modulation signal envelope with the reference voltage and output a first TDD synchronization signal. The input terminal of the NOT gate is coupled to the output terminal of the high-speed comparator, and is used to invert the first TDD synchronization signal and output the second TDD synchronization signal.

2. The TDD synchronization circuit according to claim 1, characterized in that, The radio frequency detector is configured to output a first voltage when the radio frequency coupled signal is in the transmission time domain and to output a second voltage when it is in the reception time domain; wherein the first voltage is greater than the second voltage.

3. The TDD synchronization circuit according to claim 2, characterized in that, The reference voltage is set between the first voltage and the second voltage.

4. A frequency conversion circuit, characterized in that, include: The TDD synchronization circuit as described in any one of claims 1-3; The first radio frequency switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal output by the TDD synchronization circuit, is used to separate the public network transmit and receive combined signal from the radio frequency coupler into a public network transmit signal and a public network receive signal. The second radio frequency switch, controlled by the first TDD synchronization signal and the second TDD synchronization signal, is used to combine or separate the processed private network transmission signal from the private network reception signal from the antenna. Radio frequency local oscillator circuit, used to generate radio frequency local oscillator signal; The upconverter has its input terminal coupled to the public network transmission signal output terminal of the first RF switch and the output terminal of the RF local oscillator circuit, and is used to upconvert the public network transmission signal to the private network transmission frequency band. A power amplifier, with its input terminal coupled to the output terminal of the upconverter and its output terminal coupled to the second RF switch, is used to amplify the private network transmission signal after upconversion. A low-noise amplifier, with its input coupled to the second RF switch, is used to amplify the private network received signal from the antenna; The downconverter has its input terminal coupled to the output terminal of the low-noise amplifier and the output terminal of the RF local oscillator circuit, and its output terminal coupled to the first RF switch. It is used to downconvert the private network received signal to the public network received frequency band.

5. The frequency conversion circuit according to claim 4, characterized in that, The radio frequency local oscillator circuit includes: a temperature-compensated crystal oscillator, a phase-locked loop, and a microcontroller; The output terminal of the temperature-compensated crystal oscillator is coupled to the reference clock input terminal of the phase-locked loop to provide a reference clock signal; The microcontroller communicates with the phase-locked loop (PLL) via a serial peripheral interface to configure and control the PLL to output the radio frequency local oscillator signal at a specified frequency.

6. The frequency conversion circuit according to claim 4, characterized in that, The operating states of the first RF switch and the second RF switch are complementaryly controlled by the first TDD synchronization signal and the second TDD synchronization signal to achieve switching of the transceiver channel.

7. The frequency conversion circuit according to claim 4, characterized in that, The enable terminal of the power amplifier and / or the enable terminal of the low-noise amplifier are coupled to the TDD synchronization circuit to control its on or off according to the first TDD synchronization signal and / or the second TDD synchronization signal.

8. A private network module, characterized in that, include: Public network module, radio frequency coupler, antenna interface, and frequency conversion circuit as described in any one of claims 4-7; The RF output terminal of the public network module is coupled to the input terminal of the RF coupler; The direct output terminal of the RF coupler is coupled to the signal input terminal of the frequency conversion circuit, and its coupled output terminal is used to provide an RF coupling signal to the outside. The signal output / input terminal of the frequency conversion circuit is coupled to the antenna interface.

9. The private network module according to claim 8, characterized in that, The input terminal of the TDD synchronization circuit in the frequency conversion circuit is externally connected to the coupling output terminal of the radio frequency coupler to receive the radio frequency coupling signal.

10. The private network module according to claim 8, characterized in that, The public network module operates in the TDD mobile communication frequency band.

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