A signal conversion system and method

Abstract

The application provides a signal conversion system and method, and relates to the technical field of signal modulation.The signal conversion system comprises a diplexer, a receiving filter, a mixer, and a transmitting filter, wherein the transmitting filter comprises a harmonic filter; a receiving end of the diplexer, an input end of the receiving filter, an output end of the receiving filter, and an input end of the mixer are sequentially connected to form a signal receiving link; an output end of the mixer, an input end of the harmonic filter, an output end of the harmonic filter, and a transmitting end of the diplexer are sequentially connected to form a signal transmitting link; the signal receiving link extracts an input signal of an initial frequency, and transmits the input signal to the mixer; the mixer generates a difference frequency signal; the signal transmitting link extracts an output signal of a target frequency from the difference frequency signal, suppresses harmonic interference of the output signal, and feeds the output signal into the diplexer.The application at least solves the problem that it is difficult to simultaneously guarantee high isolation, signal purity, and reliability in the prior art.The application is suitable for a signal conversion scene.

Description

Technical Field

[0001] This invention relates to the field of signal modulation technology, and in particular to a signal conversion system and method. Background Technology

[0002] Against the backdrop of deepening the co-construction and sharing of wireless networks between China Telecom and China Unicom, they have achieved a single mid-frequency network for both 4G (4th generation mobile communication technology) and 5G (5th generation mobile communication technology). Provinces across the country are actively promoting low-frequency network sharing to fully leverage the advantages of wide-area coverage and deep penetration of low-frequency signals, further address coverage shortcomings, and improve overall network quality. Currently, the low-frequency networks of both parties primarily cover deep coverage in urban areas and wide coverage in rural areas. However, in actual deployment, some urban areas (such as underground parking lots) and vast rural areas within the province are only covered by the 800MHz single-band of China Telecom. At the same time, a large number of user devices in the existing network, represented by some older terminals, IoT modules, and specific industry terminals (such as some vehicle-to-everything (V2X) devices), do not support the 800MHz band. This contradiction leads to the dilemma of "network coverage but no terminal access" or "terminals but no suitable network," severely restricting the full realization of the effectiveness of the shared low-frequency network.

[0003] The existing general-purpose RF frequency conversion technology or wideband adjustable scheme for low-frequency narrow-interval (e.g., 100MHz) conversion has the following problems: (1) The isolation design between the input and output ends is limited, making it difficult to fully suppress crosstalk between the input and output signals. Its out-of-band noise suppression capability usually cannot meet the requirements of higher suppression ratio (e.g., ≥60dBc) in high signal-to-noise ratio scenarios. The signal isolation is insufficient and interference is easy to occur. (2) Improper mixer selection or bias design leads to significant nonlinear distortion (e.g., intermodulation distortion), affecting signal quality, causing the error vector magnitude (EVM) to be too large, the modulation accuracy to deteriorate, the frequency conversion linearity to be improved, and the signal distortion to be obvious. (3) There are deficiencies in suppressing near-end image interference and balancing cost and performance. (4) There is still room for improvement in the efficiency optimization of power amplifiers. When operating at rated output power, the power consumption and temperature rise are relatively significant, often requiring additional heat dissipation devices, which is not conducive to the miniaturization and cost control of equipment. The power efficiency is low and there is heat dissipation pressure. (5) The local oscillator is not good enough in key indicators such as phase noise (e.g., -85dBc / Hz@1kHz), which affects the spectral purity and frequency stability of the output signal after frequency conversion, making it difficult to meet the communication scenarios with more stringent signal quality requirements.

[0004] In summary, existing general-purpose RF frequency conversion technologies or wideband adjustable solutions for low-frequency narrow-interval conversion suffer from insufficient signal isolation, making them prone to interference; conversion linearity needs improvement, resulting in significant signal distortion; power efficiency is low, leading to heat dissipation issues; and the local oscillator signal quality cannot meet high-order requirements. Therefore, existing general-purpose RF frequency conversion technologies or wideband adjustable solutions for low-frequency narrow-interval conversion are often structurally complex and costly. They are also prone to filter design challenges due to the proximity of image interference frequencies (such as 2600MHz) to the signal frequency band, making it difficult to simultaneously ensure high isolation and signal purity while meeting the stringent requirements for equipment cost, power consumption, and reliability in large-scale network deployments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the prior art by providing a signal conversion system and method that can achieve low-interference and high-quality signal conversion.

[0006] In a first aspect, the present invention provides a signal conversion system, including a duplexer, a receiving filter, a mixer, and a transmitting filter. The transmitting filter includes a harmonic filter. The duplexer has an antenna end, a receiving end, and a transmitting end. The receiving end of the duplexer, the input end of the receiving filter, the output end of the receiving filter, and the input end of the mixer are connected in sequence to form a signal receiving link. The output end of the mixer, the input end of the harmonic filter, the output end of the harmonic filter, and the transmitting end of the duplexer are connected in sequence to form a signal transmitting link. The antenna end of the duplexer is used to receive external signals. The signal receiving link is used to extract an input signal with an initial frequency from the external signal and transmit the input signal to the mixer. The mixer is used to mix the input signal with a local oscillator signal of a preset frequency to generate a difference frequency signal. The signal transmitting link is used to extract an output signal with a target frequency from the difference frequency signal, suppress harmonic interference on the output signal, and feed the output signal into the duplexer through the transmitting end of the duplexer. The antenna end of the duplexer is also used to transmit the output signal.

[0007] Preferably, the signal conversion system further includes a phase-locked loop frequency synthesizer, and the input of the mixer is also connected to the phase-locked loop frequency synthesizer. The phase-locked loop frequency synthesizer is used to generate a local oscillator signal of a preset frequency, and the harmonic filter is used to extract the output signal and suppress harmonic interference on the output signal.

[0008] Preferably, the receiving filter includes a pre-selection filter, which is used to extract the input signal at the initial frequency and suppress image interference on the input signal.

[0009] Preferably, the signal receiving link further includes a low-noise amplifier (LNA), the input of which is connected to the output of a preselection filter, and the output of which is connected to the input of a mixer. The LNA is used to amplify the input signal.

[0010] Preferably, the transmit filter further includes a channel selection filter, the input of which is connected to the output of the mixer, and the output of which is connected to the input of the harmonic filter. The channel selection filter is used to extract the output signal of the target frequency and to suppress spurious signals in the output signal.

[0011] Preferably, the signal transmission link further includes a Class AB power amplifier, the input of which is connected to the output of the channel selection filter, and the output of which is connected to the input of the harmonic filter. The Class AB power amplifier is used to amplify the output signal.

[0012] Preferably, the initial frequency is 800MHz and the target frequency is 900MHz.

[0013] Secondly, the present invention also provides a signal conversion method, comprising: receiving an external signal; extracting an input signal of an initial frequency from the external signal; mixing the input signal with a local oscillator signal of a preset frequency to generate a difference frequency signal; extracting an output signal of a target frequency from the difference frequency signal; suppressing harmonic interference on the output signal; and transmitting the output signal after harmonic interference suppression.

[0014] This invention provides a signal conversion system and method that achieves isolation between the pre-conversion and post-conversion signals, isolation between multiple frequency signals before conversion, and isolation between multiple frequency signals after conversion through a signal receiving link and a signal transmitting link formed by a duplexer, a receiving filter, a mixer, and a transmitting filter. By introducing a harmonic filter, unwanted frequency components are further suppressed, improving the spectral purity of the signal and enhancing signal quality. Therefore, this invention can achieve low-interference and high-quality signal conversion. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a signal conversion system according to Embodiment 1 of the present invention;

[0016] Figure 2 This is an example diagram of the radio frequency front-end module in Embodiment 1 of the present invention;

[0017] Figure 3 This is an example diagram of the frequency synthesis module in Embodiment 1 of the present invention;

[0018] Figure 4This is a flowchart of a signal conversion method according to Embodiment 2 of the present invention;

[0019] Figure 5 This is a flowchart of another signal conversion method according to Embodiment 2 of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] It is understood that the specific embodiments and accompanying drawings described herein are merely for explaining the invention and are not intended to limit the invention.

[0022] It is understood that, without conflict, the various embodiments and features in the embodiments of the present invention can be combined with each other.

[0023] It is understood that, for ease of description, only the parts related to the present invention are shown in the accompanying drawings, while the parts unrelated to the present invention are not shown in the drawings.

[0024] It is understood that each unit or module involved in the embodiments of the present invention may correspond to only one entity structure, or may be composed of multiple entity structures, or multiple units or modules may be integrated into one entity structure.

[0025] It is understood that, without conflict, the functions and steps marked in the flowcharts and block diagrams of this invention may occur in a different order than that marked in the accompanying drawings.

[0026] It is understood that the flowcharts and block diagrams of this invention illustrate the possible architecture, functions, and operations of systems, apparatuses, devices, and methods according to various embodiments of this invention. Each block in the flowchart or block diagram may represent a unit, module, program segment, or code, containing executable instructions for implementing the specified function. Furthermore, each block or combination of blocks in the block diagram and flowchart can be implemented using a hardware-based system to achieve the specified function, or using a combination of hardware and computer instructions.

[0027] It is understood that the units and modules involved in the embodiments of the present invention can be implemented by software or by hardware. For example, the units and modules can be located in a processor.

[0028] Example 1:

[0029] like Figure 1As shown, this embodiment provides a signal conversion system. The signal conversion system includes a duplexer, a receiving filter, a mixer, and a transmitting filter. The transmitting filter includes a harmonic filter. The duplexer has an antenna end, a receiving end, and a transmitting end. The receiving end of the duplexer, the input end of the receiving filter, the output end of the receiving filter, and the input end of the mixer are connected in sequence to form a signal receiving link. The output end of the mixer, the input end of the harmonic filter, the output end of the harmonic filter, and the transmitting end of the duplexer are connected in sequence to form a signal transmitting link. The antenna end of the duplexer is used to receive external signals. The signal receiving link is used to extract an input signal with an initial frequency from the external signal and transmit the input signal to the mixer. The mixer is used to mix the input signal with a local oscillator signal of a preset frequency to generate a difference frequency signal. The signal transmitting link is used to extract an output signal with a target frequency from the difference frequency signal, suppress harmonic interference on the output signal, and feed the output signal back into the duplexer through the transmitting end of the duplexer. The antenna end of the duplexer is also used to transmit the output signal.

[0030] Specifically, the initial frequency is 800MHz and the target frequency is 900MHz.

[0031] In this embodiment, an 800MHz to 900MHz signal conversion system is taken as an example. This system includes, but is not limited to, four core components: a radio frequency (RF) front-end module, a frequency conversion module, a filtering and amplification module, and a control and synchronization module. This embodiment solves the signal isolation and image suppression problems through a high-isolation RF front-end and an optimized single-conversion link; achieves high linearity and low power consumption through a high-efficiency, low-harmonic power amplifier and filtering design; and ensures frequency accuracy, power stability, and system maintainability through a high-stability local oscillator and intelligent monitoring and management unit.

[0032] The receiver and transmitter of a duplexer can isolate the signal before and after conversion, but cannot isolate the signals of multiple frequencies before conversion, nor can they isolate the signals of multiple frequencies after conversion. Both the receiver filter and the transmitter filter are bandpass filters. By using their built-in center frequency, they can block the passage of signals of non-center frequencies. Therefore, the bandpass filter can isolate the signals of multiple frequencies before conversion and the signals of multiple frequencies after conversion. For example, the antenna receives external signals of 800MHz, 900MHz, and 1000MHz, while simultaneously needing to transmit output signals of 600MHz, 900MHz, and 1200MHz. The 800MHz, 900MHz, and 1000MHz external signals are isolated at the receiving end, while the 600MHz, 900MHz, and 1200MHz output signals are isolated at the transmitting end. By connecting a receiving filter with a center frequency of 800MHz to the receiving end, the 900MHz and 1000MHz external signals can be blocked, allowing only the 800MHz external signal to be extracted and transmitted. Similarly, by connecting a transmitting filter with a center frequency of 900MHz to the transmitting end, the 600MHz and 1200MHz output signals can be blocked, allowing only the 900MHz output signal to be transmitted. In other words, this embodiment can construct an RF front-end module by connecting the receiving and transmitting filters to the receiving and transmitting ends of a duplexer, respectively.

[0033] like Figure 2 As shown, the RF front-end module includes a high-isolation bandpass filter bank and a duplexer. The high-isolation bandpass filter bank consists of at least one 800MHz receive bandpass filter and at least one 900MHz transmit bandpass filter. The 800MHz receive bandpass filter is used to receive only 800MHz input signals, and the 900MHz transmit bandpass filter is used to transmit only 900MHz output signals, thereby separating the 800MHz input signal and the 900MHz output signal with high isolation, preferably not less than 65dB. The RX (Receive) link between the duplexer and the 800MHz receive bandpass filter allows the 800MHz input signal received at the antenna end to pass smoothly from the duplexer to the 800MHz receive bandpass filter, while blocking the 900MHz signal transmitted at the antenna end to avoid interference from the transmitted signal to the receiver. The TX (Transmit) link between the duplexer and the 900MHz transmit bandpass filter allows the 900MHz output signal to pass smoothly from the 900MHz transmit bandpass filter to the duplexer, while blocking the 800MHz signal received at the antenna end to avoid interference from the received signal to the transmitter.

[0034] Optionally, the signal conversion system also includes a phase-locked loop frequency synthesizer, the input of the mixer is also connected to the phase-locked loop frequency synthesizer, the phase-locked loop frequency synthesizer is used to generate a local oscillator signal of a preset frequency, and the harmonic filter is used to extract the output signal and suppress harmonic interference on the output signal.

[0035] In this embodiment, a frequency conversion module is formed by connecting a mixer and a phase-locked loop (PLL) frequency synthesizer. The frequency conversion module employs a high-linearity mixer and a PLL frequency synthesizer to form a superheterodyne architecture for single-conversion, which is the core of the frequency conversion in this embodiment. Figure 3 As shown, the phase-locked loop frequency synthesizer generates a 1700MHz local oscillator signal with stable frequency and low phase noise (i.e., Figure 3 The local oscillator frequency), the mixer takes the 800MHz input signal (i.e., Figure 3 The RF signal (in the image) is mixed with the 1700MHz local oscillator signal, and the difference frequency component (1700MHz-800MHz=900MHz) is used to generate a difference frequency signal. This embodiment, by using a single-conversion scheme with a 1700MHz local oscillator, achieves the design goals of minimizing the number of devices, reducing link complexity, and optimizing overall power consumption and cost while ensuring effective suppression of 2600MHz image interference. It is particularly suitable for large-scale coverage enhancement deployment scenarios. The main frequency of the difference frequency signal is 900MHz, but in the actual mixing process, in addition to the 900MHz difference frequency component, there may be other frequency signals, such as sum frequency components and other frequency components generated by nonlinearity. Therefore, this embodiment uses a 900MHz transmit bandpass filter to block signals of other frequencies in the difference frequency signal, allowing only the 900MHz output signal in the difference frequency signal to pass smoothly. In addition, this embodiment uses a harmonic filter with a fixed center frequency of 900MHz as the 900MHz transmit bandpass filter. While blocking signals of other frequencies in the difference frequency signal and allowing only the 900MHz output signal in the difference frequency signal to pass smoothly, it can further suppress harmonic interference in the output signal and improve the signal quality of the 900MHz output signal.

[0036] It should be noted that the phase noise of the 1700MHz local oscillator signal generated by the phase-locked loop frequency synthesizer is no higher than -100dBc / Hz at a frequency offset of 1kHz.

[0037] Specifically, the receiving filter includes a pre-selection filter, which is used to extract the input signal at the initial frequency and suppress image interference on the input signal.

[0038] In this embodiment, a pre-selection filter with a fixed center frequency of 800MHz is used as the 800MHz receiving bandpass filter in the RF front-end module. Similarly, like a harmonic filter, while allowing only the 800MHz signal from the external signal to pass, it can further suppress image interference of the 800MHz input signal, improving the signal quality of the 800MHz input signal. This embodiment creatively employs a 1700MHz local oscillator single-conversion architecture, pushing the image frequency to 2600MHz, far from the operating frequency band. This allows for effective suppression using a conventional, low-cost 800MHz pre-selection filter, fundamentally solving the core interference problem of low-frequency narrow-interval conversion.

[0039] Optionally, the signal receiving link also includes a low-noise amplifier (LNA), the input of which is connected to the output of a preselection filter, and the output of which is connected to the input of a mixer. The LNA is used to amplify the input signal.

[0040] Optionally, the transmit filter also includes a channel selection filter, the input of which is connected to the output of the mixer, and the output of which is connected to the input of the harmonic filter. The channel selection filter is used to extract the output signal of the target frequency and to suppress spurious signals in the output signal.

[0041] In this embodiment, the input of the channel selection filter is connected to the output of the mixer. The core function of the channel selection filter is to accurately and with a high suppression ratio extract the required 900MHz output signal from the rich spectral components generated by the mixer (including the required 900MHz difference frequency signal, 1700MHz local oscillator leakage, 2500MHz sum frequency component, and other spurious signals). Its bandwidth is set according to the channel bandwidth requirements of the communication system (e.g., 3MHz or 5MHz). Using a bandpass filter with a fixed center frequency of 900MHz as the channel selection filter, similarly to a harmonic filter, it blocks signals of other frequencies in the difference frequency signal, allowing only the 900MHz output signal in the difference frequency signal to pass smoothly, while further suppressing spurious signals in the output signal, thus improving the signal quality of the 900MHz output signal. This embodiment abandons complex multi-stage frequency conversion or tunable designs, using a fixed-frequency 1700MHz local oscillator and a fixed-frequency 900MHz channel selection filter to form a simplified single-conversion link, significantly reducing the number of components, insertion loss, and potential failure points, achieving high reliability and low power consumption.

[0042] Optionally, the signal transmission link also includes a Class AB power amplifier, the input of which is connected to the output of the channel selection filter, and the output of which is connected to the input of the harmonic filter. The Class AB power amplifier is used to amplify the output signal.

[0043] In this embodiment, the filtering and amplification module is responsible for purifying and boosting the power of the signals before and after frequency conversion, respectively. It is crucial for ensuring the spectral purity and transmission quality of the input and output signals. Located at both ends of the frequency conversion module, it specifically includes one stage of input filtering, one stage of signal amplification, two stages of output filtering, and one stage of power amplification. The channel selection filter and harmonic suppression filter serve as both the 900MHz transmit bandpass filter in the RF front-end module and the two-stage output filters in the filtering and amplification module. The preselection filter serves as both the 800MHz receive bandpass filter in the RF front-end module and the first stage of input filtering in the filtering and amplification module.

[0044] The input of the power amplifier is connected to the output of the channel selection filter. This embodiment preferably uses a Class AB linear power amplifier with integrated Automatic Level Control (ALC) circuitry. The ALC circuit dynamically adjusts the amplifier gain by monitoring the output power sampling in real time, thereby stabilizing the final output power at a preset value (e.g., +30dBm ± 0.5dB), effectively handling input signal fluctuations and preventing overdrive.

[0045] The input of the harmonic suppression filter is connected to the output of the power amplifier. Its main function is to filter out out-of-band spurious emissions, such as the second harmonic (approximately 1800MHz) and third harmonic (approximately 2700MHz), generated by the nonlinear characteristics of the power amplifier. This ensures that the output 900MHz signal conforms to strict spectral emission template specifications, preventing interference with other frequency bands. A Class AB power amplifier with integrated automatic level control (ALC) is used, combined with a dedicated fixed 900MHz output filter for harmonic suppression. This optimizes overall power efficiency while maintaining output signal linearity and spectral purity.

[0046] It should be noted that the control and synchronization module is the intelligent management unit of the signal conversion system, ensuring the stable and reliable operation of the signal conversion system and performing necessary information exchange with the network side. Its core includes an embedded control unit and device management firmware embedded within it. The embedded control unit is, for example, an MCU (Microcontroller Unit). The control unit acquires key parameters in real time through an analog-to-digital converter (ADC). When parameters are abnormal (such as over-temperature, over-power, or loss of lock-up), it executes protective actions such as power reduction or shutdown and generates an alarm. These parameters include, but are not limited to: input / output signal power (for ALC), power amplifier temperature, power supply voltage, and reflected power (for VSWR monitoring). The control unit configures a phase-locked loop (PLL) via a digital interface (such as SPI) to ensure rapid locking and stabilization of the 1700MHz local oscillator. The digital interface, such as SPI (Serial Peripheral Interface), controls the gain of the power amplifier through a digital-to-analog converter (DAC) or digital potentiometer, achieving automatic level control (ALC) to stabilize the output power at a preset value. The control unit connects to the network management system via a communication interface (such as RS-485, Ethernet, or a wireless module). Its core function is to receive remote commands (such as remote switching, power level adjustment, and diagnostic testing) and report device status and alarm information. This embodiment transforms the control logic from complex "dynamic frequency switching" to intelligent management centered on status monitoring, parameter stabilization, fault protection, and network communication. This allows the signal conversion system to function as a manageable node in the network, responding to network optimization strategies (e.g., the network can instruct it to enter a low-power mode during periods of low traffic), rather than being a complex device requiring dynamic environmental adaptation.

[0047] The RF technologies relied upon in this embodiment, such as the single-conversion superheterodyne architecture, phase-locked loop frequency synthesis, and filtering amplification, are all fundamental technologies in the communications field that have been developed over decades and are extremely mature. All the core components required to implement this embodiment, including surface acoustic wave filters at specific frequencies, a 1700MHz phase-locked loop frequency synthesizer chip, a linear mixer, a Class AB power amplifier, and a microcontroller, are standard commercial off-the-shelf products in the electronics market. The supply chain is mature, stable, and has numerous suppliers, fundamentally eliminating the risks associated with technology implementation and material acquisition. The hardware implementation of the signal conversion system is based on conventional RF printed circuit board (PCB) design and surface mount technology (SMT) soldering processes. The circuit design can utilize multi-layer boards to achieve strict impedance control and electromagnetic shielding. All components are compatible with automated mounting production lines, meaning that the product, from design to production, does not rely on special or customized processes and can be manufactured quickly, on a large scale, and with high yield using the existing mature electronics manufacturing supply chain. All key performance indicators defined in this embodiment, such as conversion loss, image rejection ratio, output power, error vector magnitude (EVM), and local oscillator phase noise, can be standardized and repeatedly verified using general-purpose RF test instruments such as spectrum analyzers, signal generators, and vector network analyzers. The clear technical path and quantifiable testing methods effectively guide R&D, shorten development cycles, and ensure product performance consistency and reliability. This embodiment is not a broad technical exploration, but rather a solution precisely addressing the specific market contradiction between "800MHz network coverage for telecommunications" and "terminals not supporting 800MHz." Given the deep sharing of 4G / 5G networks and the massive connectivity of IoT terminals, this need is urgent and widespread. This embodiment directly targets application scenarios that can be quickly implemented, such as enhanced network coverage and compatibility with older equipment, with a clear market entry point and definite commercial value. By adopting a design philosophy of fixed frequency and simplified links, the device significantly reduces failure points and improves hardware reliability. The integrated intelligent monitoring and management functions support remote status query and fault alarm, reducing the difficulty and cost of on-site operation and maintenance. Its high reliability and easy maintenance characteristics fully meet the requirements of large-scale deployment and long-term stable operation of communication infrastructure equipment.

[0048] This embodiment provides a signal conversion system that achieves isolation between the pre-conversion signal and the post-conversion signal, isolation between multiple frequency signals before conversion, and isolation between multiple frequency signals after conversion through a signal receiving link and a signal transmitting link formed by a duplexer, a receiving filter, a mixer, and a transmitting filter. By introducing a harmonic filter, it helps to further suppress unnecessary frequency components, improve the spectral purity of the signal, enhance signal quality, and achieve low-interference and high-quality signal conversion.

[0049] Example 2:

[0050] like Figure 4 or Figure 5 As shown, this embodiment provides a signal conversion method. The signal conversion method includes:

[0051] S101 receives external signals.

[0052] S102 extracts the initial frequency input signal from the external signal.

[0053] In this embodiment, an initial frequency of 800MHz is taken as an example. The receiver and transmitter of the duplexer can isolate the signal before and after conversion, but cannot isolate the signals of multiple frequencies before conversion, nor can they isolate the signals of multiple frequencies after conversion. Both the receiver filter and the transmitter filter are bandpass filters, which can block signals of non-center frequencies from passing through through their built-in center frequency. Therefore, the bandpass filter can achieve isolation between signals of multiple frequencies before conversion and isolation of signals of multiple frequencies after conversion. For example: The antenna receives external signals of 800MHz, 900MHz, and 1000MHz, and at the same time, the antenna also needs to transmit output signals of 600MHz, 900MHz, and 1200MHz. The external signals of 800MHz, 900MHz, and 1000MHz are isolated at the receiving end, and the output signals of 600MHz, 900MHz, and 1200MHz are isolated at the transmitting end. By connecting a receiving filter with a center frequency of 800MHz to the receiving end, the external signals of 900MHz and 1000MHz can be blocked, and only the external signal of 800MHz can be extracted and transmitted. By connecting a transmitting filter with a center frequency of 900MHz to the transmitting end, the output signals of 600MHz and 1200MHz can be blocked, and only the output signal of 900MHz can be transmitted.

[0054] In this embodiment, a pre-selection filter with a fixed center frequency of 800MHz serves as both an 800MHz receiving bandpass filter and a first-stage input filter. While allowing only the 800MHz signal from the external signal to pass through, it can further suppress image interference of the 800MHz input signal, thereby improving the signal quality of the 800MHz input signal.

[0055] It should be noted that in this embodiment, the input terminal of the low-noise amplifier (LNA) is connected to the output terminal of the preselection filter, and the output terminal of the LNA is connected to the input terminal of the mixer to amplify the input signal.

[0056] S103 mixes the input signal with a local oscillator signal of a preset frequency to generate a difference frequency signal.

[0057] In this embodiment, taking a preset frequency of 1700MHz as an example, the phase-locked loop frequency synthesizer (i.e., Figure 5 The 1700MHz local oscillator source in the middle generates a 1700MHz local oscillator signal with stable frequency and low phase noise (i.e., Figure 3 The local oscillator frequency), the mixer takes the 800MHz input signal (i.e., Figure 3 The radio frequency signal in the signal is mixed with the 1700MHz local oscillator signal, and the difference frequency component (1700MHz-800MHz=900MHz) is used to generate the difference frequency signal.

[0058] S104 extracts the target frequency output signal from the difference frequency signal and performs harmonic interference suppression on the output signal.

[0059] In this embodiment, the main frequency of the difference frequency signal is 900MHz. However, in the actual mixing process, in addition to the 900MHz difference frequency component, there may be other frequency signals, such as sum frequency components and other frequency components generated by nonlinearity. Therefore, this embodiment uses a 900MHz transmit bandpass filter to block other frequency signals in the difference frequency signal, allowing only the 900MHz output signal of the difference frequency signal to pass smoothly. Furthermore, this embodiment uses a harmonic filter with a fixed center frequency of 900MHz as the 900MHz transmit bandpass filter. While blocking other frequency signals in the difference frequency signal and allowing only the 900MHz output signal of the difference frequency signal to pass smoothly, it can further suppress harmonic interference in the output signal, thereby improving the signal quality of the 900MHz output signal.

[0060] It should be noted that the channel selection filter and harmonic suppression filter serve as both a 900MHz transmit bandpass filter and a two-stage output filter. The input of the channel selection filter is connected to the output of the mixer, the input of the power amplifier is connected to the output of the channel selection filter, and the input of the harmonic suppression filter is connected to the output of the power amplifier. From the rich spectral components generated by the mixer (including the required 900MHz difference frequency signal, 1700MHz local oscillator leakage, 2500MHz sum frequency component, and other spurious signals), the required 900MHz output signal is accurately extracted with a high suppression ratio. The ALC circuit dynamically adjusts the amplifier gain by monitoring the sampling of the output power in real time, thereby stabilizing the final output power at a preset value (e.g., +30dBm±0.5dB), effectively dealing with input signal fluctuations and preventing overdrive. The harmonic suppression filter filters out out-of-band spurious emissions such as the second harmonic (approximately 1800MHz) and third harmonic (approximately 2700MHz) generated by the nonlinear characteristics of the power amplifier, ensuring that the output 900MHz signal conforms to the strict spectrum emission template specifications and avoids interference with other frequency bands. The system employs a Class AB power amplifier with integrated automatic level control (ALC) and a fixed 900MHz output filter dedicated to harmonic suppression, which optimizes the overall energy efficiency while ensuring the linearity and spectral purity of the output signal.

[0061] S105 transmits the output signal after harmonic interference suppression.

[0062] This embodiment provides a signal conversion method that performs signal conversion through a signal receiving link and a signal transmitting link formed by connecting a duplexer, a receiving filter, a mixer, and a transmitting filter. This achieves isolation between the signal before and after conversion, isolation between multiple frequency signals before conversion, and isolation between multiple frequency signals after conversion. By introducing a harmonic filter, it helps to further suppress unnecessary frequency components, improve the spectral purity of the signal, enhance signal quality, and achieve low-interference and high-quality signal conversion.

[0063] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A signal conversion system, characterized in that, Includes duplexers, receiver filters, mixers, and transmitter filters. Transmit filters include harmonic filters. The duplexer has an antenna end, a receiver end, and a transmitter end. The receiving end of the duplexer, the input end of the receiving filter, the output end of the receiving filter, and the input end of the mixer are connected in sequence to form a signal receiving link. The output terminal of the mixer, the input terminal of the harmonic filter, the output terminal of the harmonic filter, and the transmitter terminal of the duplexer are connected in sequence to form a signal transmission link. The antenna end of the duplexer is used to receive external signals; The signal receiving link is used to extract an input signal of initial frequency from the external signal and transmit the input signal to the mixer; The mixer is used to mix the input signal with a local oscillator signal of a preset frequency to generate a difference frequency signal; The signal transmission link is used to extract the target frequency output signal from the difference frequency signal, suppress harmonic interference of the output signal, and feed the output signal into the duplexer through the transmitting end of the duplexer; The antenna end of the duplexer is also used to transmit the output signal.

2. The signal conversion system according to claim 1, characterized in that, It also includes a phase-locked loop frequency synthesizer. The input of the mixer is also connected to a phase-locked loop frequency synthesizer. A phase-locked loop frequency synthesizer is used to generate a local oscillator signal of a preset frequency. The harmonic filter is used to extract the output signal and suppress harmonic interference in the output signal.

3. The signal conversion system according to claim 1, characterized in that, The receiving filter includes a preselection filter. The pre-selection filter is used to extract the input signal at the initial frequency and suppress image interference on the input signal.

4. The signal conversion system according to claim 3, characterized in that, The signal receiving link also includes a low-noise amplifier (LNA). The input of the low-noise amplifier (LNA) is connected to the output of the preselection filter, and the output of the LNA is connected to the input of the mixer. A low-noise amplifier (LNA) is used to amplify the input signal.

5. The signal conversion system according to claim 1, characterized in that, The transmit filter also includes a channel selection filter. The input of the channel selection filter is connected to the output of the mixer, and the output of the channel selection filter is connected to the input of the harmonic filter. The channel selection filter is used to extract the output signal of the target frequency and suppress spurious signals on the output signal.

6. The signal conversion system according to claim 5, characterized in that, The signal transmission link also includes a Class AB power amplifier. The input of the Class AB power amplifier is connected to the output of the channel selection filter, and the output of the Class AB power amplifier is connected to the input of the harmonic filter. The Class AB power amplifier is used to amplify the output signal.

7. The signal conversion system according to claim 1, characterized in that, The initial frequency is 800MHz, and the target frequency is 900MHz.

8. A signal conversion method, characterized in that, include: Receive external signals; Extract the input signal with the initial frequency from the external signal; The input signal is mixed with a local oscillator signal of a preset frequency to generate a difference frequency signal; Extract the target frequency output signal from the difference frequency signal, and suppress harmonic interference in the output signal; Transmit the output signal after harmonic interference suppression.

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