Receiver

Abstract

This invention provides a receiver, comprising: a bandpass filter, a mixer, a switching filter, and a local oscillator module; the output of the bandpass filter is connected to the input of the switching filter, and the output of the switching filter is connected to the signal input of the mixer; the local oscillator signal input of the mixer is connected to the output of the local oscillator module; the input of the bandpass filter is used to receive a radio frequency signal; the bandpass filter is used to output frequency components within a preset frequency range of the radio frequency signal and suppress image frequency signals of other frequency components; the switching filter is used to pre-filter the output signal of the bandpass filter based on the frequency range corresponding to the selected filtering command when a selected filtering command is received; the local oscillator module is used to output a high local oscillator signal with the frequency corresponding to the local oscillator command when a local oscillator command is received; the mixer is used to mix the output signal of the switching filter and the local oscillator signal to generate a preset intermediate frequency signal.

Description

Technical Field

[0001] This utility model relates to the field of receiver technology, and in particular to a receiver. Background Technology

[0002] In wireless communication systems, the receiver is an indispensable key device, and its performance directly affects the quality and reliability of the communication system. With the continuous development of technology, receiver technology has also been constantly advancing, evolving from the initial analog receivers to today's digital receivers, with increasingly powerful functions and a wider range of applications.

[0003] The most common drawback encountered in receiver design is the presence of significant interference after frequency synthesis and mixing, particularly image interference. Interference signals from the image frequency of the RF signal relative to the local oscillator frequency are down-converted to the intermediate frequency band by the mixer and cannot be filtered out by channel selection filters, thus degrading the quality of the received signal. Utility Model Content

[0004] The main purpose of this invention is to provide a receiver designed to reduce image interference.

[0005] To achieve the above objectives, the receiver proposed in this utility model includes: Bandpass filter, mixer, switching filter and local oscillator module; The output of the bandpass filter is connected to the input of the switching filter, and the output of the switching filter is connected to the signal input of the mixer; the local oscillator signal input of the mixer is connected to the output of the local oscillator module; the input of the bandpass filter is used to receive radio frequency signals. The bandpass filter is used to output the frequency components within a preset frequency range of the radio frequency signal and suppress the image frequency signals of other frequency components. The switching filter is used to pre-filter the output signal of the bandpass filter based on the frequency range corresponding to the selection filtering instruction when a selection filtering instruction is received. The local oscillator module is used to output a high local oscillator signal with the frequency corresponding to the local oscillator command when a local oscillator command is received. The mixer is used to mix the output signal of the switching filter and the local oscillator signal to generate a preset intermediate frequency signal.

[0006] Optionally, the switching filter includes: a first single-pole multi-throw switch, a second single-pole multi-throw switch, and multiple filters; The input terminal of the first single-pole multi-throw switch is connected to the output terminal of the bandpass filter; the input terminals of multiple filters are connected one-to-one to the multiple output terminals of the first single-pole multi-throw switch; the output terminals of multiple filters are connected one-to-one to the multiple input terminals of the second single-pole multi-throw switch; the output terminal of the second single-pole multi-throw switch is connected to the signal input terminal of the mixer; the controlled terminal of the first single-pole multi-throw switch is connected to the controlled terminal of the second single-pole multi-throw switch. The passband bandwidths of each filter do not overlap; The first single-pole multi-throw switch and the second single-pole multi-throw switch are used to connect the filter corresponding to the selection filtering command to the path of the bandpass filter and the mixer when the selection filtering command is received, so that the filter pre-filters the output signal of the bandpass filter.

[0007] Optionally, the receiver further includes: a crystal filter bank; The input terminal of the crystal filter bank is connected to the output terminal of the mixer; The crystal filter bank is used to select the intermediate frequency signal output by the mixer and switch it to the crystal filter corresponding to the channel selection command when a channel selection command is received.

[0008] Optionally, the receiver further includes: a surface acoustic wave (SAW) filter; The input terminal of the surface acoustic wave filter is connected to the output terminal of the mixer, and the output terminal is connected to the input terminal of the crystal filter bank. The surface acoustic wave (SAW) filter is used to suppress other frequency components by allowing the intermediate frequency signal component of a preset frequency to pass through.

[0009] Optionally, the receiver further includes: a limiter; The input terminal of the limiter is used to receive radio frequency signals; the output terminal of the limiter is connected to the input terminal of the bandpass filter.

[0010] Optionally, the receiver further includes: a first low-noise amplifier; The input of the first low-noise amplifier is connected to the output of the bandpass filter, and the output is connected to the input of the first single-pole multi-throw switch.

[0011] Optionally, the receiver further includes: a first intermediate frequency amplifier; The input terminal of the first intermediate frequency amplifier is connected to the output terminal of the surface acoustic wave filter, and the output terminal is connected to the input terminal of the crystal filter bank.

[0012] Optionally, the receiver further includes: a power adjustment module; The input terminal of the power regulation module is connected to the output terminal of the crystal filter bank; The power adjustment module is used to adjust the intermediate frequency signal output by the crystal filter bank to the power value corresponding to the power command when a power command is received.

[0013] Optionally, the power regulation module includes: a voltage-controlled attenuator and a second intermediate frequency amplifier; The input terminal of the voltage-controlled attenuator is connected to the output terminal of the crystal filter bank, and the output terminal is connected to the input terminal of the second intermediate frequency amplifier. The voltage-controlled attenuator is used to adjust the intermediate frequency signal output by the crystal filter bank to the power value corresponding to the power command when a power command is received.

[0014] Optionally, the receiver further includes: a second low-noise amplifier; The input terminal of the second low-noise amplifier is connected to the output terminal of the switching filter, and the output terminal is connected to the input terminal of the mixer.

[0015] This invention provides a receiver comprising: a bandpass filter, a mixer, a switching filter, and a local oscillator module. The output of the bandpass filter is connected to the input of the switching filter, and the output of the switching filter is connected to the signal input of the mixer. The local oscillator signal input of the mixer is connected to the output of the local oscillator module. The input of the bandpass filter is used to receive a radio frequency (RF) signal. The bandpass filter outputs frequency components within a preset frequency range of the RF signal, suppressing image frequency signals of other frequency components. The switching filter, upon receiving a selective filtering command, pre-filters the output signal of the bandpass filter based on the frequency range corresponding to the selective filtering command. The local oscillator module, upon receiving a local oscillator command, outputs a high local oscillator signal with the frequency corresponding to the local oscillator command. The mixer mixes the output signal of the switching filter and the local oscillator signal to generate a preset intermediate frequency (IF) signal. This invention uses a bandpass filter to perform a first filtering of the RF signal, initially filtering out image frequencies, and then uses a switching filter to perform a second filtering, further suppressing image frequency interference. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the receiver of the present invention in the first embodiment; Figure 2 This is a schematic diagram of the second embodiment of the receiver of this utility model; Figure 3 This is a schematic diagram of the first structure of the receiver of the third embodiment of the present invention; Figure 4 This is a schematic diagram of the second structure of the receiver of the present invention, in the third embodiment. Figure 5 This is a schematic diagram of the third structure of the receiver of the present invention.

[0018] Explanation of icon numbers: 10, Bandpass filter; 20, Switching filter; 30, Mixer; 40, Local oscillator module; 50, Crystal filter bank; 60, Surface AWACS filter; 70, Limiter; 210, First single-pole multi-throw switch; 220, Second single-pole multi-throw switch.

[0019] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0021] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in this utility model embodiment are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0022] In this utility model, unless otherwise explicitly specified and limited, the terms "connection," "fixing," etc., should be interpreted broadly. For example, "fixing" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0023] Furthermore, in this utility model, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this utility model.

[0024] The fundamental reason for the image frequency lies in the nonlinear characteristics and multiplier principle of mixer 30. The core task of the receiver is to down-convert the received high-frequency radio frequency (RF) signal to a lower and fixed intermediate frequency (IF) for subsequent amplification and filtering. This process is performed by mixer 30. Mixer 30 requires an input signal (RF) and a local oscillator (LO) signal: mixer 30 multiplies these two signals, and its output contains new frequency components, mainly their sum frequency (RF+LO) and difference frequency (|RF-LO|). We use a filter to select only the difference frequency signal we need, which is the IF signal. The key point is that mixer 30 cannot distinguish between a signal with an IF frequency one MHz higher than the local oscillator frequency and a signal with an IF frequency one MHz lower than the local oscillator frequency because their absolute difference frequencies are equal.

[0025] The harm caused by image frequencies is significant and direct, primarily manifesting as signal interference and signal quality degradation. If a strong signal happens to be located at the image frequency, it will be "mistranslated" into an intermediate frequency (IF) signal by mixer 30 and superimposed on the truly useful IF signal. This leads to a severe drop in the signal-to-noise ratio (SNR), with the received signal being mixed with useless interference. This can range from minor issues like noise and increased bit error rate to the complete inability to demodulate useful information.

[0026] To solve the above problems, this utility model proposes a receiver, such as... Figure 1 As shown, in the first embodiment, the receiver includes: Bandpass filter 10, mixer 30, switching filter 20 and local oscillator module 40; The output terminal of the bandpass filter 10 is connected to the input terminal of the switching filter 20, and the output terminal of the switching filter 20 is connected to the signal input terminal of the mixer 30; the local oscillator signal input terminal of the mixer 30 is connected to the output terminal of the local oscillator module; the input terminal of the bandpass filter 10 is used to receive radio frequency signals. The bandpass filter 10 is used to output the frequency components within a preset frequency range in the radio frequency signal and suppress the image frequency signals of other frequency components. The switching filter 20 is used to pre-filter the output signal of the bandpass filter 10 based on the frequency range corresponding to the selection filtering instruction when a selection filtering instruction is received. The local oscillator module 40 is used to output a high local oscillator signal with the frequency corresponding to the local oscillator command when a local oscillator command is received. The mixer 30 is used to mix the output signal of the switching filter 20 and the local oscillator signal to generate a preset intermediate frequency signal.

[0027] It should be noted that, in order to solve the above-mentioned problems, this embodiment uses the local oscillator module 40 to provide a high local oscillator signal based on the characteristics of the image frequency, so that the following frequency relationship exists: radio frequency signal frequency value < local oscillator signal frequency value < image frequency. A high local oscillator signal means that the frequency of the local oscillator signal provided by the local oscillator is higher than the radio frequency signal frequency value. It is easy to understand that the difference between the local oscillator signal frequency value and the radio frequency signal frequency value is equal to the difference between the image frequency and the local oscillator signal frequency value. That is, the difference between the image frequency and the radio frequency signal frequency value is twice the intermediate frequency signal frequency value.

[0028] After determining the preset intermediate frequency signal, the R&D personnel can determine the preset frequency range and the corresponding local oscillator signal, and select and adjust the bandpass filter 10 accordingly. It is easy to understand that, in order to reduce image interference, the preset frequency range does not include the image frequency. Specifically, the maximum value of the preset frequency range is less than the local oscillator signal. In this embodiment, the input terminal of the bandpass filter 10 is connected to the radio frequency signal, and the bandpass filter 10 outputs the frequency components of the radio frequency signal within the preset frequency range, suppressing image frequency signals of other frequency components.

[0029] This embodiment uses a bandpass filter 10 to suppress and filter potential image frequencies, increasing the proportion of frequency components within a preset frequency range in the radio frequency signal. This embodiment also uses the switching filter 20 to further filter the frequency components within the preset frequency range. The core function of the switching filter group 20 is to dynamically select the most suitable narrowband filter based on the frequency range corresponding to the selected filtering command before the signal enters the mixer 30, performing "preselection filtering" on the signal. Its main purpose is to suppress image frequency interference to the extreme, while also filtering out other out-of-band interference and spurious signals generated locally.

[0030] While the bandpass filter 10 (e.g., 108-137MHz) can initially filter out out-of-band noise, its potentially wide bandwidth may result in insufficient attenuation of the image signal. For a specific channel (e.g., 125MHz), its image frequency (e.g., 125MHz+2) is also important. Although the frequency (21.4MHz ≈ 167.8MHz) is out of band, the distance is not far enough, and a fixed bandpass filter 10 may not be sufficient to attenuate 167.8MHz. If this mirrored interference signal is strong, the residual energy entering mixer 30 will still cause interference.

[0031] Furthermore, within the entire receiver operating frequency band (e.g., 108-137MHz), the image frequencies corresponding to different channels are different. A fixed filter cannot provide optimal and consistent image suppression performance for all channels. The switching filter 20 can dynamically select the most suitable narrowband filter according to the frequency range corresponding to the selected filter command, providing better image suppression performance.

[0032] The local oscillator module 40 is connected to the local oscillator signal input terminal of the mixer 30 and is used to output a local oscillator signal with a frequency corresponding to the local oscillator command to the mixer 30.

[0033] The mixer 30 is used to mix the output signal of the switching filter 20 and the local oscillator signal to generate a preset intermediate frequency signal.

[0034] This invention provides a receiver comprising: a bandpass filter 10, a mixer 30, a switching filter 20, and a local oscillator module 40; the output of the bandpass filter 10 is connected to the input of the switching filter 20, and the output of the switching filter 20 is connected to the signal input of the mixer 30; the local oscillator signal input of the mixer 30 is connected to the output of the local oscillator module 40; the input of the bandpass filter 10 is used to receive a radio frequency signal; the bandpass filter 10 is used to output frequency components within a preset frequency range of the radio frequency signal and suppress image frequency signals of other frequency components; the switching filter 20 is used to pre-filter the output signal of the bandpass filter 10 based on the frequency range corresponding to the selected filtering command when a selected filtering command is received; the local oscillator module 40 is used to output a high local oscillator signal with the frequency corresponding to the local oscillator command when a local oscillator command is received; the mixer 30 is used to mix the output signal of the switching filter 20 and the local oscillator signal to generate a preset intermediate frequency signal. This invention uses a bandpass filter 10 to perform a first filtering of the radio frequency signal, initially filtering out the image frequency, and then uses a switching filter 20 to perform a second filtering, further suppressing the image frequency interference.

[0035] In the second embodiment, as Figure 2 As shown, the switching filter 20 includes: a first single-pole multi-throw switch 210, a second single-pole multi-throw switch 220, and multiple filters; The input terminal of the first single-pole multi-throw switch 210 is connected to the output terminal of the bandpass filter 10; the input terminals of multiple filters are connected one-to-one to the multiple output terminals of the first single-pole multi-throw switch 210; the output terminals of multiple filters are connected one-to-one to the multiple input terminals of the second single-pole multi-throw switch 220; the output terminal of the second single-pole multi-throw switch 220 is connected to the signal input terminal of the mixer 30; the controlled terminal of the first single-pole multi-throw switch 210 is connected to the controlled terminal of the second single-pole multi-throw switch 220. The passband bandwidths of each filter do not overlap; The first single-pole multi-throw switch 210 and the second single-pole multi-throw switch 220 are used to connect the filter corresponding to the selection filtering command to the path of the bandpass filter 10 and the mixer 30 when the selection filtering command is received, so that the filter pre-filters the output signal of the bandpass filter 10.

[0036] It should be noted that the switching filter 20 consists of three main parts: 1. An input single-pole multi-throw switch (first single-pole multi-throw switch 210) is connected to the output of bandpass filter 10.

[0037] 2. A group of parallel bandpass filters 10 (multiple filters): each filter has a narrow passband and they do not overlap, together covering the entire receiving frequency band.

[0038] 3. An output single-pole multi-throw switch (second single-pole multi-throw switch 220) is connected to the signal input terminal of mixer 30.

[0039] The throw positions of the first single-pole multi-throw switch 210 and the second single-pole multi-throw switch 220 are controlled synchronously, like a linked selector. Upon receiving the selection filter command, the first single-pole multi-throw switch 210 and the second single-pole multi-throw switch 220 synchronously switch to the path of the filter corresponding to the selection filter command; the filter corresponding to the selection filter command is connected to the path of the bandpass filter 10 and the mixer 30, so that the filter pre-filters the output signal of the bandpass filter 10.

[0040] Because each filter has a narrow bandwidth, only signals with frequencies within the passband of that narrow-band filter can pass through with minimal loss. Mirror frequencies, signals from other channels, and various spurious interferences far from the passband are severely attenuated by this narrow-band filter. In practical applications, this is equivalent to equipping each channel with an independent filter. The 20 sets of switched filters, by sharing switches and circuitry, implement the functions of multiple filters in a single structure, achieving a good balance between performance and integration / cost.

[0041] In the third embodiment, as Figure 3 As shown, the receiver further includes: a crystal filter bank 50; The input terminal of the crystal filter bank 50 is connected to the output terminal of the mixer 30; The crystal filter bank 50 is used to select the intermediate frequency signal output by the mixer 30 and switch it to the crystal filter corresponding to the channel selection command when a channel selection command is received.

[0042] It needs to be explained that after the RF signal is down-converted to a fixed intermediate frequency (IF, which can be 21.4MHz in this case) by mixer 30, although out-of-band interference such as image interference is greatly suppressed, the signal still faces challenges: there may be other strong signals on frequencies very close to the target channel, which have also been down-converted to the vicinity of the IF. A filter with an extremely narrow bandwidth and very steep edges is needed to separate the target channel and suppress interference from adjacent channels.

[0043] The crystal filter bank 50 is not a single filter, but a modular functional component integrating multiple independent crystal filter units, a switching switch, and a matching impedance matching network. The multiple crystal filter units typically contain two or more crystal filters with the same center frequency but different bandwidths. In one example, two filters are configured: a 25 kHz bandwidth crystal filter for standard wide-channel communication, and an 8.33 kHz bandwidth crystal filter for narrow-channel communication requiring higher channel utilization.

[0044] Each filter unit is typically a multi-section crystal filter. It consists of multiple quartz crystal resonators, capacitors, and inductors arranged in a specific network structure (such as trapezoidal or lattice). The more sections, the better the filter's performance (flatter passband and steeper stopband attenuation). The center frequencies of all filter units are precisely tuned to the receiver's intermediate frequency, for example, 21.4 MHz.

[0045] The switching switch is key to implementing the "group" function, responsible for guiding the signal path to the selected filter; it is an electronically controlled selector. It has one common input and multiple outputs (each connected to a different filter). The switching switch is used to switch the signal path to the corresponding crystal filter based on received shape channel instructions; the selected crystal filter performs the final, decisive filtering of the signal. Only frequency components strictly within its passband (i.e., the target channel) can pass through, while adjacent channel signals and noise on both sides of the passband are drastically attenuated. Switches can include single-pole multi-throw switches, RF relays, or PIN diode switches, etc.

[0046] like Figure 4As shown, the receiver further includes: a surface acoustic wave filter 60; The input terminal of the surface acoustic wave filter 60 is connected to the output terminal of the mixer 30, and the output terminal is connected to the input terminal of the crystal filter bank 50. The surface acoustic wave (SAW) filter 60 is used to suppress other frequency components by allowing the intermediate frequency signal component of a preset frequency to pass through.

[0047] It should be noted that the surface acoustic wave (SAW) filter 60 is located between the mixer 30 and the crystal filter bank 50. It is used to perform a stable, preset bandpass filter on the fixed intermediate frequency signal after the mixer 30, and to "pre-screen" the subsequent crystal filter, playing a key filtering role that connects the preceding and following signals.

[0048] After the signal is down-converted to an intermediate frequency (e.g., 21.4MHz) by mixer 30, although the main image interference has been suppressed by the preceding 20 sets of switching filters, the signal output by mixer 30 still has some problems: 1. Mixing product contamination: Mixer 30 is a nonlinear device whose output includes not only the useful 21.4 MHz difference frequency signal, but also a large number of useless frequency components such as radio frequency (RF), local oscillator (LO) and their sum frequency (RF+LO) and higher harmonics.

[0049] 2. Wideband noise: The mixing process itself also generates wideband noise.

[0050] The working principle of the surface acoustic wave (SAW) filter 60 is as follows: The input electrical signal is applied to a piezoelectric crystal material (such as lithium niobate or quartz) through an interdigital transducer (IDT). Due to the inverse piezoelectric effect, electrical energy is converted into surface acoustic waves (a type of mechanical wave that propagates along the surface of a material); the sound waves propagate on the substrate surface. Their propagation characteristics and the shape, spacing, and number of electrodes of the IDT determine which frequencies of sound waves can be effectively excited and received. Sound waves of specific frequencies will resonate and superimpose, while sound waves of other frequencies will cancel each other out or attenuate. The filtered surface acoustic waves propagate to the interdigital transducer at the output end, where they are converted back into an electrical signal through the direct piezoelectric effect. This "electric-sound-electric" conversion process naturally achieves frequency filtering.

[0051] The surface acoustic wave (SAW) filter 60 effectively filters out stray signals such as the sum frequency (RF+LO) generated during mixing and suppresses the leakage of the local oscillator signal into the intermediate frequency path through the mixer 30, preventing these components from interfering with subsequent circuits or causing nonlinear distortion. Furthermore, by removing a large amount of strong out-of-band interference in advance, the SAW filter 60 provides a "cleaner" operating environment for the crystal filter, preventing it from being driven into the nonlinear region or saturating, thus ensuring the accuracy and stability of its filtering performance.

[0052] like Figure 5As shown, the receiver further includes: a limiter 70; The input terminal of the limiter 70 is used to receive radio frequency signals; the output terminal of the limiter 70 is connected to the input terminal of the bandpass filter 10.

[0053] A limiter 70 is installed at the input of the bandpass filter 10 to prevent power reflection or excessive received signals from damaging subsequent circuitry. The receiver antenna may receive signals (RF signals) with extremely wide strengths, ranging from very weak (e.g., -120dBm) to very strong (e.g., +20dBm or even higher). If these strong signals directly enter the receiver front-end, it can have disastrous consequences. For example, the mixer 30 in the subsequent stage performs best when operating in its optimal linear region. An excessively strong input signal will saturate it, causing it to enter the nonlinear region, resulting in a sharp drop in gain, effectively "blocking" the entire receiver and preventing it from receiving any weak signals. It can also directly burn out the diodes in the mixer 30, causing permanent hardware damage and leading to complete receiver failure.

[0054] Limiter 70 has minimal impact on the signal (with minimal insertion loss) when the input signal power is below a certain design threshold (called the limiting threshold); when the input power exceeds this threshold, it clamps the output signal power to a fixed, lower level. Limiter 70 protects downstream circuitry by limiting the RF signal power.

[0055] The receiver further includes: a first low-noise amplifier; The input terminal of the first low-noise amplifier is connected to the output terminal of the bandpass filter 10, and the output terminal is connected to the input terminal of the first single-pole multi-throw switch 210.

[0056] The radio frequency (RF) signal received from the antenna is extremely weak, possibly as low as -120 dBm or even weaker. These signals are very easily drowned out by noise generated by the subsequent circuitry itself, making them unrecognizable and undemodulated. To address this issue, a first low-noise amplifier is used at the beginning of the signal link to amplify the initially filtered weak RF signal while adding as little of its own noise as possible, thereby establishing a noise performance benchmark for the entire receiver.

[0057] Every component in the receiver (filter, amplifier, mixer 30, etc.) introduces additional noise while processing the signal. Frith's law states that the noise figure of the entire system is primarily determined by the noise figure and gain of the first-stage circuitry. Therefore, using a low-noise amplifier helps reduce the overall noise of the receiver.

[0058] The receiver further includes: a first intermediate frequency amplifier; The input terminal of the first intermediate frequency amplifier is connected to the output terminal of the surface acoustic wave filter 60, and the output terminal is connected to the input terminal of the crystal filter bank 50.

[0059] The first intermediate frequency amplifier amplifies the signal filtered by the surface acoustic wave filter 60 at a fixed intermediate frequency to compensate for losses in the link and provide sufficient signal driving capability for subsequent key filtering stages, while maintaining the purity of the signal.

[0060] When a signal passes through a surface acoustic wave (SAW) filter, it incurs a certain insertion loss (typically a few dB of attenuation). While the SAW filter removes noise, the signal energy is also weakened. Link transmission loss: The signal also experiences minor losses as it propagates along PCB transmission lines, connectors, and other paths. If these losses are not compensated for, directly feeding the attenuated signal into the subsequent crystal filter bank 50 will result in an excessively low signal amplitude, making it easily masked by noise from the subsequent circuitry.

[0061] The receiver further includes: a power adjustment module; The input terminal of the power regulation module is connected to the output terminal of the crystal filter bank 50; The power adjustment module is used to adjust the intermediate frequency signal output by the crystal filter bank 50 to the power value corresponding to the power command when a power command is received.

[0062] Radio frequency (RF) signal strength varies greatly, ranging from extremely weak -98 dBm to very strong -7 dBm. This difference of over 90 dB can cause serious problems. Signals that are too weak will be overwhelmed by noise, making them unrecognizable to the demodulator and increasing the bit error rate. Strong signals can overload and saturate subsequent amplifiers, filters, and even the demodulator, pushing them into the nonlinear region and causing severe signal distortion. Both FM discriminators and digital demodulation chips require a stable intermediate frequency (IF) signal to achieve optimal demodulation performance. Amplitude fluctuations directly lead to demodulated output distortion.

[0063] Therefore, this example proposes a power adjustment module that adjusts the output power of the intermediate frequency signal based on power commands, stabilizing it at a constant, optimal level regardless of variations in the strength of the input radio frequency signal. This allows the receiver to seamlessly handle input signals from -98dBm to -7dBm without saturation under strong signals or loss of signal strength under weak signals. The receiver features high dynamic range and high sensitivity.

[0064] In one example, the power regulation module includes: a voltage-controlled attenuator and a second intermediate frequency amplifier; The input terminal of the voltage-controlled attenuator is connected to the output terminal of the crystal filter bank 50, and the output terminal is connected to the input terminal of the second intermediate frequency amplifier; The voltage-controlled attenuator is used to adjust the intermediate frequency signal output by the crystal filter bank 50 to the power value corresponding to the power command when a power command is received.

[0065] It's important to explain that the attenuation of the voltage-controlled attenuator (VCA) is continuously controlled by a control voltage (i.e., a power command). A higher control voltage results in greater attenuation (and thus greater insertion loss), and vice versa. When the input signal is too strong: the main control module outputs a higher control voltage, causing the VCA to increase attenuation, thereby significantly reducing the signal strength. When the input signal is too weak: the main control module outputs a lower control voltage (even zero), causing the VCA to decrease attenuation (or even eliminate attenuation), allowing the signal to pass through with almost no loss. The VCA solves the problem of strong signal input. By attenuating before amplification, it ensures that even when receiving the strongest signal, the subsequent second intermediate frequency amplifier will not be overloaded or saturated.

[0066] The second intermediate frequency (IF) amplifier provides a fixed, stable gain (e.g., 20 dB or 30 dB). Its gain is immutable, amplifying the signal output from the VCA to a predetermined optimal level suitable for demodulator operation; if the VCA attenuates significantly, it amplifies the remaining signal; if the VCA attenuates less, it amplifies less. The second IF amplifier compensates for the insertion losses introduced by the VCA, filters, and other pre-amplifier components, and ensures that the final output signal to the demodulator has a stable and sufficiently large amplitude.

[0067] The receiver further includes: a second low-noise amplifier; The input terminal of the second low-noise amplifier is connected to the output terminal of the switching filter 20, and the output terminal is connected to the input terminal of the mixer 30.

[0068] It should be noted that the second low-noise amplifier amplifies the signal a second time after the switching filter group 20, specifically to compensate for the insertion loss of the switching filter group 20 and to provide the optimal drive level for the mixer 30, so as to optimize the conversion gain and linearity of the mixer 30.

[0069] The signal inevitably incurs insertion loss when passing through the 20 sets of switched filters. While the 20 sets of switched filters greatly suppress image and out-of-band interference, they themselves attenuate useful signal energy. A second low-noise amplifier compensates for this loss and provides strong drive to the mixer 30; effectively counteracting the signal attenuation introduced by the 20 sets of switched filters, ensuring that valuable signal energy is not excessively weakened before reaching the mixer 30. Furthermore, it provides sufficient drive power to the mixer 30, enabling it to operate at its optimal state of high conversion gain and good linearity, thereby improving the efficiency and quality of the down-conversion.

[0070] The above description is only an optional embodiment of the present utility model and does not limit the patent scope of the present utility model. All equivalent structural transformations made under the concept of the present utility model and using the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present utility model.

Claims

1. A receiver, characterized by The receiver includes: Bandpass filter, mixer, switching filter and local oscillator module; The output of the bandpass filter is connected to the input of the switching filter, and the output of the switching filter is connected to the signal input of the mixer; the local oscillator signal input of the mixer is connected to the output of the local oscillator module; the input of the bandpass filter is used to receive radio frequency signals. The bandpass filter is used to output the frequency components within a preset frequency range of the radio frequency signal and suppress the image frequency signals of other frequency components. The switching filter is used to pre-filter the output signal of the bandpass filter based on the frequency range corresponding to the selection filtering instruction when a selection filtering instruction is received. The local oscillator module is used to output a high local oscillator signal with the frequency corresponding to the local oscillator command when a local oscillator command is received. The mixer is used to mix the output signal of the switching filter and the local oscillator signal to generate a preset intermediate frequency signal.

2. The receiver of claim 1, wherein, The switching filter includes: a first single-pole multi-throw switch, a second single-pole multi-throw switch, and multiple filters; The input terminal of the first single-pole multi-throw switch is connected to the output terminal of the bandpass filter; the input terminals of multiple filters are connected one-to-one to the multiple output terminals of the first single-pole multi-throw switch; the output terminals of multiple filters are connected one-to-one to the multiple input terminals of the second single-pole multi-throw switch; the output terminal of the second single-pole multi-throw switch is connected to the signal input terminal of the mixer; the controlled terminal of the first single-pole multi-throw switch is connected to the controlled terminal of the second single-pole multi-throw switch. The passband bandwidths of each filter do not overlap; The first single-pole multi-throw switch and the second single-pole multi-throw switch are used to connect the filter corresponding to the selection filtering command to the path of the bandpass filter and the mixer when the selection filtering command is received, so that the filter pre-filters the output signal of the bandpass filter.

3. The receiver of claim 2, wherein, The receiver further includes: a crystal filter bank; The input terminal of the crystal filter bank is connected to the output terminal of the mixer; The crystal filter bank is used to select the intermediate frequency signal output by the mixer and switch it to the crystal filter corresponding to the channel selection command when a channel selection command is received.

4. The receiver of claim 3, wherein, The receiver also includes: a surface acoustic wave filter; The input terminal of the surface acoustic wave filter is connected to the output terminal of the mixer, and the output terminal is connected to the input terminal of the crystal filter bank. The surface acoustic wave (SAW) filter is used to suppress other frequency components by allowing the intermediate frequency signal component of a preset frequency to pass through.

5. The receiver of claim 4, wherein, The receiver also includes: a limiter; The input terminal of the limiter is used to receive radio frequency signals; the output terminal of the limiter is connected to the input terminal of the bandpass filter.

6. The receiver of claim 5, wherein, The receiver further includes: a first low-noise amplifier; The input terminal of the first low-noise amplifier is connected to the output terminal of the bandpass filter, and the output terminal is connected to the input terminal of the first single-pole multi-throw switch.

7. The receiver of claim 6, wherein, The receiver further includes: a first intermediate frequency amplifier; The input terminal of the first intermediate frequency amplifier is connected to the output terminal of the surface acoustic wave filter, and the output terminal is connected to the input terminal of the crystal filter bank.

8. The receiver of claim 3, wherein, The receiver further includes: a power adjustment module; The input terminal of the power regulation module is connected to the output terminal of the crystal filter bank; The power adjustment module is used to adjust the intermediate frequency signal output by the crystal filter bank to the power value corresponding to the power command when a power command is received.

9. The receiver of claim 8, wherein, The power regulation module includes: a voltage-controlled attenuator and a second intermediate frequency amplifier; The input terminal of the voltage-controlled attenuator is connected to the output terminal of the crystal filter bank, and the output terminal is connected to the input terminal of the second intermediate frequency amplifier. The voltage-controlled attenuator is used to adjust the intermediate frequency signal output by the crystal filter bank to the power value corresponding to the power command when a power command is received.

10. A receiver as claimed in any one of claims 1 to 9, characterized in that The receiver further includes: a second low-noise amplifier; The input terminal of the second low-noise amplifier is connected to the output terminal of the switching filter, and the output terminal is connected to the input terminal of the mixer.

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