A method and circuit for spurious signal processing of local oscillator signals

Abstract

This invention relates to the field of radio frequency communication technology, specifically to a method and circuit for spurious signal processing of local oscillator signals. It can be used for spurious signal suppression in 5G / 6G base stations, radio frequency communication systems, millimeter-wave terminals, and satellite ground station frequency conversion channels. The spurious signal processing method proposed in this invention obtains the frequency of the local oscillator signal using the target intermediate frequency signal and radio frequency signal. Then, based on the phase detection frequency, it calculates the interference intensity of the first type of spurious signal in each frequency band of the local oscillator signal, i.e., the frequency of the first type of spurious signal present in each frequency band. Based on this interference intensity, the local oscillator signal is divided into frequency bands. Then, a filter is used in each frequency band to suppress the first type of spurious signal, resulting in a cleaner local oscillator signal. This invention solves the technical problem in the prior art where, when a local oscillator link generates local oscillator signals of different frequencies, it is impossible to specifically filter out spurious signals based on their characteristics.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication technology, and more specifically, to a method and circuit for spurious signal processing of local oscillator signals. Background Technology

[0002] In the internal design of various devices or modules in wireless communication, electronic measurement, and radar systems, frequency mixing is a crucial step in signal processing. Therefore, the performance of the mixing circuit directly determines the sensitivity, dynamic range, and anti-interference capability of the entire system, device, or module for signal processing. However, spurious signals generated during the mixing process are amplified and diffused into subsequent circuits or systems, directly leading to a degraded system performance. This is especially true for systems with high sensitivity requirements, where spurious signals can cause significant interference.

[0003] Among existing spurious signal processing techniques, some methods add a filter to the intermediate frequency (IF) signal obtained after mixing the RF and local oscillator (LO) signals to filter spurious signals. The drawback of this approach is that when spurious signals from the LO signal overlap with the mixed IF signal, subsequent filtering cannot remove them, and spurious signals leak into the IF signal link, causing greater impact on subsequent links. Other methods use fixed filtering to remove spurious signals in the LO signal link before mixing the LO and RF signals. This fixed filtering method typically only removes spurious signals outside the fixed filter's frequency band, failing to remove spurious signals within its band. Still other methods use multi-band filtering, but this mechanically divides the LO signal frequency into multiple bands without considering the different spurious signal characteristics generated when the LO signal is generated in different frequency bands. This segmented processing method groups two LO signals with different frequencies and spurious characteristics into one band, resulting in spurious signals still not being filtered out and still leaking into subsequent links.

[0004] The stray signals of the local oscillator signal include two types of stray signals. The first type of stray signal is generated when the local oscillator signal is generated through a phase-locked loop, based on the phase detection frequency. Unlike other signals, the local oscillator signal carries a frequency of at a distance N times the phase detection frequency. The stray signal, when the Nth harmonic signal of the phase detection frequency satisfies At this time, the spurious signal will fall into the intermediate frequency band, causing interference to the intermediate frequency signal; the second type of spurious signal is the interference of the local oscillator signal output by the phase-locked loop to the intermediate frequency signal, which will generate interference between the local oscillator signal and the intermediate frequency signal. spurious signals.

[0005] Existing technologies generally employ a filter to suppress spurious signals after obtaining the intermediate frequency (IF) signal. However, this method is not very effective at suppressing spurious signals. Alternatively, a filter can be used to remove spurious signals after the local oscillator (LO) signal is generated. However, this approach does not take advantage of the characteristic that the intensity of the first type of spurious signal interference changes with the target IF and RF signals. Instead, it divides the LO signal frequency band based on the change in spurious signal interference intensity and then processes spurious signals in different frequency bands. This directly results in poor spurious signal suppression, as spurious signals still diffuse into the IF signal. This can cause significant interference for systems with high sensitivity requirements. Summary of the Invention

[0006] The purpose of this application is to provide a spurious signal processing circuit that solves the technical problem in the prior art where, when a local oscillator link generates local oscillator signals of different frequencies, it is impossible to specifically filter out spurious signals based on their characteristics. This invention can be used for spurious signal suppression in 5G / 6G base stations, radio frequency communication systems, millimeter-wave terminals, and satellite ground station frequency conversion channels.

[0007] To solve the above-mentioned technical problems, the solution adopted in this application is as follows: A method for spurious signal processing of a local oscillator signal includes the following steps: Based on the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal, the frequency range of the local oscillator signal is obtained using the frequency conversion formula. Based on the phase detection frequency, calculate the interference intensity of the first type of spurious signal in different frequency bands of the local oscillator signal; Based on the intensity of the first type of spurious signal interference, the sub-frequency band division interval of the local oscillator signal is determined, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands; Based on the bandwidth requirements of radio frequency signal transmission, the bandwidth of the switching filter is determined and the switching filter is designed. Each sub-filter in the switching filter corresponds to a sub-band of the local oscillator signal. The local oscillator signal of the local oscillator signal in the corresponding band is subjected to Type I spurious signal suppression processing to obtain a relatively pure local oscillator signal. The relatively pure local oscillator signal and the radio frequency signal are mixed to obtain the target intermediate frequency signal; An adaptive bandwidth filter is designed based on the frequency of the target intermediate frequency signal and the frequency of the local oscillator signal. When the local oscillator signal generates a second type of spurious signal at the intermediate frequency signal, the adaptive bandwidth filter adjusts its bandwidth to filter out the second type of spurious signal caused by the local oscillator signal.

[0008] When the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal change, and the frequency range of the required local oscillator signal exceeds the frequency range of the current local oscillator signal, the above steps are executed again to update the frequency range of the local oscillator signal and divide it into frequency bands.

[0009] Preferably, the local oscillator signal sub-frequency band division interval is determined based on the intensity of the first type of spurious signal interference, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands. The specific implementation method is as follows: Using formula The distribution and magnitude of the first type of spurious signal at different frequency positions of the local oscillator signal were calculated; After obtaining the distribution and magnitude of the first type of spurious signal, the local oscillator signal is divided into different sub-bands within the local oscillator signal frequency range according to the distribution and magnitude of the first type of spurious signal; The sub-band division rule is as follows: the distance between the first type of spurious signal contained in each sub-band and the center frequency of the sub-band is less than the distance between the first type of spurious signal and the center frequency of any other sub-band, and the span of each sub-band is not less than the instantaneous bandwidth of the radio frequency signal.

[0010] Preferably, the determination of the bandwidth of the switching filter and the use of the local oscillator signal of the switching filter for first-type spurious signal suppression are specifically implemented as follows: Based on the frequency of the first type of spurious signal within the sub-band and the frequency range of the sub-band, the bandwidth of the filter is set. The bandwidth of the filter covers the frequency range of the local oscillator signal within the frequency band that does not contain the first type of spurious signal, and the bandwidth of the filter is not less than the instantaneous bandwidth of the radio frequency signal.

[0011] Preferably, the bandwidth of the filter is adjusted according to the interference intensity of the first type of spurious signal in the sub-band. When the sub-band is a low-frequency sub-band, the frequency of the first type of spurious signal is close to the local oscillator signal. At this time, the bandwidth of the filter is narrowed to exclude the first type of spurious signal from the bandwidth range of the filter, leaving only the local oscillator signal. When the frequency difference between the first type of spurious signal and the local oscillator signal becomes larger, the bandwidth range of the filter can be expanded.

[0012] Preferably, the method for filtering out the second type of spurious signals using a filter is as follows: The frequency of the second type of spurious signal caused by the local oscillator signal to the target intermediate frequency signal is calculated using the following formula:

[0013] Based on the frequency difference between the second type of spurious signal and the target intermediate frequency signal The frequency difference for:

[0014] Based on frequency difference Select a filter so that the target intermediate frequency signal falls within the filter's passband, while the second type of spurious signal falls outside the filter's passband.

[0015] A spurious signal processing circuit for a local oscillator signal includes an RF receiving circuit, a local oscillator generation circuit, and a local oscillator filtering circuit. The reference signal output terminal of the RF receiving circuit is connected to the reference signal receiving terminal of the local oscillator generation circuit, and the local oscillator signal output terminal of the local oscillator generation circuit is connected to the local oscillator signal receiving terminal of the local oscillator filtering circuit. The local oscillator filtering circuit includes at least two sub-filtering circuits for spurious filtering of local oscillator signals in different frequency bands. The radio frequency receiving circuit receives the radio frequency signal and generates a reference signal according to the frequency of the radio frequency signal. The local oscillator generation circuit receives the reference signal and generates a local oscillator signal according to the reference signal. After the local oscillator signal is generated, the sub-filter circuit that performs spurious filtering on the local oscillator signal in the specified frequency band starts to work and performs spurious filtering on the local oscillator signal.

[0016] Preferably, the local oscillator generation circuit includes a phase-locked loop chip U120, a signal amplification chip U34, and an RF switch chip U180; The first signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the signal amplifier chip U34; the second signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the radio frequency switch chip U180, and the generated local oscillator signal is output to the signal amplifier chip U34 and the radio frequency switch chip U180.

[0017] Preferably, the RF receiving circuit includes an RF signal connector U128 and a filtering circuit. The RF signal connector U128 is connected to the RF signal output terminal of an external device to receive external RF signals and generate a reference signal. Simultaneously, it outputs the reference signal to the phase-locked loop (PLL) chip U120. The PLL chip U120 outputs a local oscillator signal that matches the frequency of the RF signal based on the frequency of the reference signal. One end of the filtering circuit is connected to the reference signal output terminal of the RF signal connector U128, and the other end of the filtering circuit is connected to the reference signal input terminal of the PLL chip U120 to filter the reference signal.

[0018] Preferably, the local oscillator filter circuit includes a first filter circuit, a second filter circuit, and a third filter circuit; The first filtering circuit includes filter U170 and filter U171. After filter U170 and filter U171 are connected in series, one end is connected to the signal output pin RFOUT4 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT1 of RF switch chip U174. The second filtering circuit includes filter U172 and filter U173. After filter U172 and filter U173 are connected in series, one end is connected to the signal output pin RFOUT3 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT2 of RF switch chip U174. The third filtering circuit includes filter U176 and filter U177. After being connected in series, one end of filter U176 and filter U177 is connected to the signal output pin RFOUT1 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT4 of RF switch chip U174.

[0019] The technical solution of this application has at least the following advantages and beneficial effects: 1. The spurious signal processing method proposed in this invention uses the target intermediate frequency signal and radio frequency signal to obtain the frequency of the local oscillator signal, and then calculates the interference intensity of the first type of spurious signal in each frequency band based on the phase detection frequency, that is, the frequency of the first type of spurious signal existing in each frequency band. Based on this interference intensity, the local oscillator signal is divided into frequency bands, and then the first type of spurious signal is suppressed by the filter of each frequency band to obtain a cleaner local oscillator signal. When the radio frequency signal, the target intermediate frequency signal, and the phase detection frequency change in different application scenarios, the corresponding local oscillator signal frequency band and its corresponding filter parameters can be adjusted according to this method. The method has universality. After the local oscillator signal and the radio frequency signal are mixed to obtain the intermediate frequency signal, the second type of spurious signal generated on the intermediate frequency signal varies depending on the frequency of the radio frequency signal. The corresponding processing methods are also different. The method provided by this invention proposes adaptive bandwidth filters or switching filters. When the radio frequency signal frequency is low, the bandwidth of the filter should be reduced; while when the radio frequency signal frequency is high, there are no special requirements for the bandwidth of the filter, as long as it meets the transmission bandwidth of the radio frequency signal. The second type of spurious signal is processed, and the spurious signal is processed in a targeted manner before and after mixing.

[0020] 2. The spurious signal processing circuit in this invention differs from traditional spurious signal processing circuits, which can only generate a local oscillator signal that matches a single frequency band of radio frequency signal. The spurious signal processing circuit disclosed in this invention can generate a local oscillator signal that covers various frequency bands. When a radio frequency signal of a certain frequency is input, it can generate a local oscillator signal that matches the frequency of the input radio frequency signal, and conduct the corresponding filter circuit to filter the spurious signal of the local oscillator signal.

[0021] 3. Unlike traditional spurious signal processing circuits that mechanically divide the frequency band of the generated local oscillator signal into fixed frequency bands without considering the different characteristics of spurious signals generated by the link that generates the local oscillator signal when it is in different frequency bands, the spurious signal processing circuit disclosed in this invention divides the frequency band of the local oscillator signal according to its different spurious characteristics in different frequency bands, and designs a filter circuit for the spurious signal of the corresponding frequency band. The designed filter circuit can better suppress the spurious signal of the local oscillator signal link in its corresponding frequency band, thereby suppressing the spurious signal before the RF signal and local oscillator signal are mixed, and preventing it from leaking into the subsequent intermediate frequency link. Attached Figure Description

[0022] Figure 1 The present invention relates to a local oscillator generation circuit and a radio frequency receiving circuit; Figures 2-4 This is the local oscillator filter circuit of the present invention; Figure 5 This is the level control circuit of the present invention; Figure 6 Example diagrams showing the selection of filters for different frequency bands in this invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. The terms "center," "upper," "lower," "inner," and "outer," indicating orientation or positional relationships based on the orientation or positional relationships shown in the figures, or the orientation or positional relationships commonly used when the product is in use, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and therefore should not be construed as a limitation on this application. It should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0025] This invention provides a method for spurious signal processing of local oscillator signals, the implementation process of which is as follows: Based on the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal, the frequency range of the local oscillator signal is obtained using the frequency conversion formula. Based on the phase detection frequency, calculate the interference intensity of the first type of spurious signal in different frequency bands of the local oscillator signal; Based on the intensity of the first type of spurious signal interference, the sub-frequency band division interval of the local oscillator signal is determined, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands; Based on the bandwidth requirements of radio frequency signal transmission, the bandwidth of the switching filter is determined and the switching filter is designed. Each sub-filter in the switching filter corresponds to a sub-band of the local oscillator signal. The local oscillator signal of the local oscillator signal in the corresponding band is subjected to Type I spurious signal suppression processing to obtain a relatively pure local oscillator signal. The relatively pure local oscillator signal and the radio frequency signal are mixed to obtain the target intermediate frequency signal; An adaptive bandwidth filter is designed based on the frequency of the target intermediate frequency signal and the frequency of the local oscillator signal. When the local oscillator signal generates a second type of spurious signal at the intermediate frequency signal, the adaptive bandwidth filter adjusts its bandwidth to filter out the second type of spurious signal caused by the local oscillator signal.

[0026] When the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal change, and the frequency range of the required local oscillator signal exceeds the frequency range of the current local oscillator signal, the above steps are executed again to update the frequency range of the local oscillator signal and divide it into frequency bands.

[0027] It is feasible to obtain the local oscillator signal frequency range based on the target intermediate frequency signal frequency and the radio frequency signal frequency range. The specific implementation method is as follows: When the target intermediate frequency signal is Radio frequency signal is At that time, the required local oscillator signal The frequency is calculated using the following formula:

[0028] For example, when the target intermediate frequency signal is 2400MHz and the radio frequency signal is 100MHz, a local oscillator signal with a frequency of 2500MHz can be generated using a phase-locked loop. The local oscillator signal and the radio frequency signal with a frequency of 100MHz are then subjected to difference frequency mixing by frequency domain subtraction to obtain the target intermediate frequency signal.

[0029] It is feasible to calculate the interference intensity of the first type of spurious signal in different frequency bands of the local oscillator signal based on the phase detection frequency. The specific implementation method is as follows: The formula for calculating Type I spurious signals is:

[0030] in, The phase detection frequency is the frequency at which the phase-locked loop generates the local oscillator signal.

[0031] It should be noted that the first type of stray signal mentioned in this invention refers to the harmonics generated by the phase-locked loop (PLL) when it generates the local oscillator signal. These harmonics are related to the phase detection frequency of the PLL, and are determined based on the phase detection frequency. Unlike other signals, the local oscillator signal carries a frequency of at a distance N times the phase detection frequency. The harmonic spurious signal, when the Nth harmonic spurious signal of the phase detection frequency satisfies At this time, the harmonic spurious signal will fall into the intermediate frequency band, causing interference to the intermediate frequency signal. Moreover, because its frequency is close to that of the target intermediate frequency signal, it is difficult to filter it out in the intermediate frequency band.

[0032] For example, when the phase detection frequency is 100MHz and N is 1, the frequency of the harmonic spurious signal is 100MHz. The frequency of this harmonic spurious signal, when superimposed with the local oscillator signal, is 2400MHz. Therefore, near the local oscillator signal at 2500MHz, there will be a harmonic spurious signal at 2400MHz. This harmonic spurious signal will leak to the intermediate frequency (IF) signal during the mixing of the RF signal and the IF signal. Since this frequency overlaps with the IF signal, it cannot be filtered out in the IF band. If the phase detection frequency changes, the frequency of the harmonic spurious signal also changes accordingly.

[0033] In some embodiments, the sub-frequency band division interval of the local oscillator signal is determined according to the intensity of the first type of spurious signal interference, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands. The specific implementation method is as follows: Using formula The distribution and magnitude of the first type of spurious signal at different frequency positions of the local oscillator signal were calculated; After obtaining the distribution and magnitude of the first type of spurious signal, the local oscillator signal is divided into different sub-bands within the local oscillator signal frequency range according to the distribution and magnitude of the first type of spurious signal; The sub-band division rule is as follows: the distance between the first type of spurious signal contained in each sub-band and the center frequency of the sub-band is less than the distance between the first type of spurious signal and the center frequency of any other sub-band, and the span of each sub-band is not less than the instantaneous bandwidth of the radio frequency signal.

[0034] This ensures that each sub-band covers the entire local oscillator signal frequency band, and that the first type of spurious signals within each sub-band can be suppressed and filtered out by the corresponding sub-band filter.

[0035] In some embodiments, the bandwidth of the switched filter is determined, and the local oscillator signal of the switched filter is used for first-type spurious signal suppression processing. The specific implementation method is as follows: Based on the frequency of the first type of spurious signal within the sub-band and the frequency range of the sub-band, the bandwidth of the filter is set. The bandwidth of the filter covers the frequency range of the local oscillator signal within the frequency band that does not contain the first type of spurious signal, and the bandwidth of the filter is not less than the instantaneous bandwidth of the radio frequency signal.

[0036] In some embodiments, the bandwidth of the filter is adjusted according to the interference intensity of the first type of spurious signal in the sub-band. When the sub-band is a low-frequency sub-band, the frequency of the first type of spurious signal is close to the local oscillator signal. At this time, the bandwidth of the filter is narrowed to exclude the first type of spurious signal from the bandwidth range of the filter, leaving only the local oscillator signal. When the frequency difference between the first type of spurious signal and the local oscillator signal becomes larger, the bandwidth range of the filter can be expanded.

[0037] For example, such as Figure 6 As shown, if the input RF signal ranges from 100MHz to 2000MHz, the target intermediate frequency signal frequency is 2400MHz, and the instantaneous bandwidth of the RF signal is better than 30MHz, then the required local oscillator signal frequency range is 2500MHz to 4400MHz. Customized segmented filtering is performed on the local oscillator signal in this frequency band. For the local oscillator signal in the 2500 MHz-2517 MHz band, the first type of spurious signal frequency is 2400 MHz, the selected filter bandwidth is 23 MHz, and the filter center frequency is 2484 MHz; in the 2504 MHz-2844 MHz band, the selected filter bandwidth is 170 MHz, and the filter center frequency is 2674MHz.

[0038] In some embodiments, a filter is used to filter out the second type of spurious signals, and the implementation method is as follows: The frequency of the second type of spurious signal caused by the local oscillator signal to the target intermediate frequency signal is calculated using the following formula:

[0039] Based on the frequency difference between the second type of spurious signal and the target intermediate frequency signal The frequency difference for:

[0040] Based on frequency difference Select a filter so that the target intermediate frequency signal falls within the filter's passband, while the second type of spurious signal falls outside the filter's passband.

[0041] It should be noted that the above-mentioned filters can be real-time bandwidth adjustable filters; multi-passband filters can also be used; multiple filters can be controlled by the chip. When in use, select the frequency-matched filter, turn it on, and filter out the first and / or second spurious signals. Example

[0042] The present invention also provides a spurious signal processing circuit for local oscillator signals, which is a feasible embodiment of the above method. The circuit includes an RF receiving circuit, a local oscillator generation circuit, and a local oscillator filtering circuit. The reference signal output terminal of the RF receiving circuit is connected to the reference signal receiving terminal of the local oscillator generation circuit, and the local oscillator signal output terminal of the local oscillator generation circuit is connected to the local oscillator signal receiving terminal of the local oscillator filtering circuit. The local oscillator filtering circuit includes at least two sub-filtering circuits for spurious filtering of local oscillator signals in different frequency bands.

[0043] The radio frequency receiving circuit receives the radio frequency signal and generates a reference signal based on the frequency of the radio frequency signal. The local oscillator generation circuit receives the reference signal and generates a local oscillator signal based on the reference signal. After the local oscillator signal is generated, the sub-filter circuit that performs spurious filtering on the local oscillator signal in the specified frequency band starts working and performs spurious filtering on the local oscillator signal.

[0044] For details, see Figure 1-5 The local oscillator generation circuit includes a phase-locked loop chip U120, a signal amplification chip U34, and an RF switch chip U180.

[0045] The first signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the signal amplifier chip U34; the second signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the radio frequency switch chip U180, and the generated local oscillator signal is output to the signal amplifier chip U34 and the radio frequency switch chip U180.

[0046] The radio frequency (RF) receiving circuit includes an RF signal connector U128 and a filtering circuit. The RF signal connector U128 is connected to the RF signal output terminal of an external device to receive external RF signals and generate a reference signal. Simultaneously, it outputs the reference signal to the phase-locked loop (PLL) chip U120. The PLL chip U120 outputs a local oscillator signal that matches the frequency of the RF signal based on the frequency of the reference signal. One end of the filtering circuit is connected to the reference signal output terminal of the RF signal connector U128, and the other end of the filtering circuit is connected to the reference signal input terminal of the PLL chip U120 to filter the reference signal.

[0047] It should be noted that the phase-locked loop chip U120 is model number LMX2594; the RF signal connector U128 is model number DBA8-5-3000-827; the signal amplifier chip U34 is model number ILA-0112E-PQ3; and the RF switch chip U180 is model number ISW-00144T-PD-CQ4.

[0048] In this embodiment, the local oscillator filter circuit includes a first filter circuit, a second filter circuit, and a third filter circuit.

[0049] The first filtering circuit includes filter U170 and filter U171. Filter U170 and filter U171 are connected in series. One end of the series connection is connected to the signal output pin RFOUT4 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT1 of RF switch chip U174. When the RF signal is between 3600 and 5542 MHz, the local oscillator signal frequency is between 6058 and 8000 MHz, and the target intermediate frequency signal is 2458 MHz, the first filtering circuit is turned on.

[0050] The second filtering circuit includes filter U172 and filter U173. Filter U172 and filter U173 are connected in series. One end of filter U172 is connected to the signal output pin RFOUT3 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT2 of RF switch chip U174. When the RF signal is between 5542 and 7242 MHz, the local oscillator signal frequency is between 8000 and 9700 MHz, and the target intermediate frequency signal is 2458 MHz, the second filtering circuit is turned on.

[0051] The third filtering circuit includes filter U176 and filter U177. After filter U176 and filter U177 are connected in series, one end is connected to the signal output pin RFOUT1 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT4 of RF switch chip U174. When the radio frequency signal is between 7242 and 8000 MHz, the local oscillator signal frequency is between 9700 and 10548 MHz, and the target intermediate frequency signal is 2458 MHz, the third filter circuit is turned on.

[0052] It should be noted that the model numbers for filter U170, U171, U172, U173, U174, U175, and U177 are as follows: U170 is HFCN3216-6010D01; U171 is LFCN3216-7200A01; U172 is HFCN-7971+; U173 is JBLF9170-3216; U176 is BFCN-1052+; and U177 is LFCW-1062+. These filters can suppress spurious signals from local oscillator signals in different frequency bands. These filters form a filtering circuit for local oscillator signals in different frequency bands. When the local oscillator signal passes through these filtering circuits, its spurious signals are suppressed.

[0053] In this embodiment, the switching on and off of each sub-filter circuit is controlled by a gating filter circuit and a level control circuit. The gating filter circuit includes RF switches F76, F85, F191, F86, F196, and F197. One end of RF switches F196 and F197 is connected to the power supply, and the other end is connected to the power input pins of RF switch chips U174 and U175, respectively, to provide operating voltage input for RF switch chips U174 and U175. One end of RF switch F76 is connected to one end of RF switch F86, and the common terminal connecting RF switches F76 and F86 is connected to the level control circuit. The level control signal output terminal of the control circuit is connected to the following: one end of RF switch F76 is connected to the IN1 pin of RF switch chip U175, and the other end of RF switch F86 is connected to the IN1 pin of RF switch chip U174; one end of RF switch F85 is connected to one end of RF switch F191, and the common terminal connecting RF switches F85 and F191 is connected to the level control signal output terminal of the level control circuit; the other end of RF switch F85 is connected to the IN2 pin of RF switch chip U174, and the other end of RF switch F191 is connected to the IN2 pin of RF switch chip U175. The level control circuit outputs a level signal to control the levels of the IN1 and IN2 pins of RF switch chips U174 and U175 respectively. When the levels of the IN1 and IN2 pins change between high and low levels, one of the first, second, and third filter circuits will be turned on.

[0054] It should be noted that the model numbers of RF switches F76, F85, F191, F86, F196, and F197 are all BKCF-1608U220M160NT-3P(22P).

[0055] Specifically, the aforementioned level control circuit includes level control chip U166, level control chip U9, and level control chip U10. The three level control chips are independent of each other and output level control signals to the radio frequency switches they control to control their output high and low levels.

[0056] It should be noted that, in this embodiment, the frequency band of the local oscillator signal can be further divided into 6500~7780MHz, 10474~11800MHz, and 11800~13000MHz bands according to the differences in its spurious characteristics in different frequency bands. The circuit structure and processing are similar to those of the above frequency bands, so they will not be described again here.

[0057] It should be noted that the above embodiments are only one feasible embodiment of the local oscillator signal spurious processing method in this invention.

[0058] It should be noted that all the electronic devices mentioned in the above embodiments are available in domestic and international markets.

[0059] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions of this invention based on the above description, and the scope of the invention is defined by the appended claims.

Claims

1. A method for spurious signal processing of a local oscillator signal, characterized in that, Includes the following steps: Based on the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal, the frequency range of the local oscillator signal is obtained using the frequency conversion formula. Based on the phase detection frequency, calculate the interference intensity of the first type of spurious signal in different frequency bands of the local oscillator signal; Based on the intensity of the first type of spurious signal interference, the sub-frequency band division interval of the local oscillator signal is determined, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands; Based on the bandwidth requirements of radio frequency signal transmission, the bandwidth of the switching filter is determined and the switching filter is designed. Each sub-filter in the switching filter corresponds to a sub-band of the local oscillator signal. The local oscillator signal of the local oscillator signal in the corresponding band is subjected to Type I spurious signal suppression processing to obtain a relatively pure local oscillator signal. The relatively pure local oscillator signal and the radio frequency signal are mixed to obtain the target intermediate frequency signal; An adaptive bandwidth filter is designed based on the frequency of the target intermediate frequency signal and the frequency of the local oscillator signal. When the local oscillator signal generates a second type of spurious signal at the intermediate frequency signal, the adaptive bandwidth filter adjusts its bandwidth to filter out the second type of spurious signal caused by the local oscillator signal. When the frequency range of the radio frequency signal and the frequency of the target intermediate frequency signal change, and the frequency range of the required local oscillator signal exceeds the frequency range of the current local oscillator signal, the above steps are executed again to update the frequency range of the local oscillator signal and divide it into frequency bands.

2. The spurious signal processing method for a local oscillator signal according to claim 1, characterized in that, Based on the intensity of the first type of spurious signal interference, the sub-frequency band division interval of the local oscillator signal is determined, and the frequency range of the local oscillator signal is divided into multiple sub-frequency bands. The specific implementation method is as follows: Using formula The distribution and magnitude of the first type of spurious signal at different frequency positions of the local oscillator signal were calculated; whereby... For phase detection frequency, The frequency of the harmonic spurious signal, The frequency representing the harmonic spurious signal is the phase detection frequency. times; After obtaining the distribution and magnitude of the first type of spurious signal, the local oscillator signal is divided into different sub-bands within the local oscillator signal frequency range according to the distribution and magnitude of the first type of spurious signal; The sub-band division rule is as follows: the distance between the first type of spurious signal contained in each sub-band and the center frequency of the sub-band is less than the distance between the first type of spurious signal and the center frequency of any other sub-band, and the span of each sub-band is not less than the instantaneous bandwidth of the radio frequency signal.

3. The spurious signal processing method for a local oscillator signal according to claim 1, characterized in that, The determination of the bandwidth of the switching filter and the use of the local oscillator signal of the switching filter for first-type spurious signal suppression are specifically implemented as follows: Based on the frequency of the first type of spurious signal within the sub-band and the frequency range of the sub-band, the bandwidth of the filter is set. The bandwidth of the filter covers the frequency range of the local oscillator signal within the frequency band that does not contain the first type of spurious signal, and the bandwidth of the filter is not less than the instantaneous bandwidth of the radio frequency signal.

4. The spurious signal processing method for a local oscillator signal according to claim 3, characterized in that, The bandwidth of the filter is adjusted according to the interference intensity of the first type of spurious signal in the sub-band. When the sub-band is a low-frequency sub-band, the frequency of the first type of spurious signal is close to the local oscillator signal. At this time, the bandwidth of the filter is narrowed to exclude the first type of spurious signal from the bandwidth range of the filter, leaving only the local oscillator signal. When the frequency difference between the first type of spurious signal and the local oscillator signal becomes larger, the bandwidth range of the filter can be expanded.

5. The spurious signal processing method for a local oscillator signal according to claim 1, characterized in that, The method for filtering out the second type of spurious signals caused by the local oscillator signal is as follows: The frequency of the second type of spurious signal caused by the local oscillator signal to the target intermediate frequency signal is calculated using the following formula: ； Calculate the frequency difference between the type II spurious signal and the target intermediate frequency signal. The frequency difference for: ； in, The frequency of the second type of spurious signal caused by the local oscillator signal to the target intermediate frequency signal. Indicates the frequency of the local oscillator signal. Indicates the frequency of the target intermediate frequency signal. This represents the frequency difference between the second type of spurious signal and the target intermediate frequency signal; Based on frequency difference Select a filter so that the target intermediate frequency signal falls within the filter's passband, while the second type of spurious signal falls outside the filter's passband.

6. A spurious signal processing circuit for a local oscillator signal, used to implement the spurious signal processing method for a local oscillator signal as described in any one of claims 1-5, characterized in that, include: Radio frequency receiving circuit, local oscillator generation circuit, local oscillator filtering circuit; The reference signal output terminal of the radio frequency receiving circuit is connected to the reference signal receiving terminal of the local oscillator generation circuit, and the local oscillator signal output terminal of the local oscillator generation circuit is connected to the local oscillator signal receiving terminal of the local oscillator filtering circuit; wherein, the local oscillator filtering circuit includes at least two sub-filtering circuits for spurious filtering of local oscillator signals of different frequency bands. The radio frequency receiving circuit receives the radio frequency signal and generates a reference signal according to the frequency of the radio frequency signal. The local oscillator generation circuit receives the reference signal and generates a local oscillator signal according to the reference signal. After the local oscillator signal is generated, the sub-filter circuit that performs spurious filtering on the local oscillator signal in the specified frequency band starts to work and performs spurious filtering on the local oscillator signal.

7. The spurious signal processing circuit for a local oscillator signal according to claim 6, characterized in that, The local oscillator generation circuit includes a phase-locked loop chip U120, a signal amplification chip U34, and an RF switch chip U180. The first signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the signal amplifier chip U34; the second signal output pin of the phase-locked loop chip U120 is connected to the signal input pin of the radio frequency switch chip U180, and the generated local oscillator signal is output to the signal amplifier chip U34 and the radio frequency switch chip U180.

8. The spurious signal processing circuit for a local oscillator signal according to claim 7, characterized in that, The radio frequency (RF) receiving circuit includes an RF signal connector U128 and a filtering circuit. The RF signal connector U128 is connected to the RF signal output terminal of an external device to receive external RF signals and generate a reference signal. Simultaneously, it outputs the reference signal to the phase-locked loop (PLL) chip U120. The PLL chip U120 outputs a local oscillator signal that matches the frequency of the RF signal based on the frequency of the reference signal. One end of the filtering circuit is connected to the reference signal output terminal of the RF signal connector U128, and the other end of the filtering circuit is connected to the reference signal input terminal of the PLL chip U120 to filter the reference signal.

9. The spurious signal processing circuit for a local oscillator signal according to claim 8, characterized in that, The local oscillator filter circuit includes a first filter circuit, a second filter circuit, and a third filter circuit; The first filtering circuit includes filter U170 and filter U171. After filter U170 and filter U171 are connected in series, one end is connected to the signal output pin RFOUT4 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT1 of RF switch chip U174. The second filtering circuit includes filter U172 and filter U173. After filter U172 and filter U173 are connected in series, one end is connected to the signal output pin RFOUT3 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT2 of RF switch chip U174. The third filtering circuit includes filter U176 and filter U177. After being connected in series, one end of filter U176 and filter U177 is connected to the signal output pin RFOUT1 of RF switch chip U175, and the other end is connected to the signal output pin RFOUT4 of RF switch chip U174.

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