CN113890547A - Low-spurious system of full-band receiver and frequency conversion selection method - Google Patents
Low-spurious system of full-band receiver and frequency conversion selection method Download PDFInfo
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Abstract
The invention provides a low-spurious system of a full-band receiver and a frequency conversion selection method, which comprise the following steps: an intermediate frequency selection module: in a receiving frequency band, analyzing and calculating various combinations which can be formed between input signals and local oscillation signals in a frequency mixer through simulation of a computer; a preselection filter division module: as a broadband radio frequency front end, the preselection filter reduces the chance of multiple signals entering the receiver at the same time, and reduces second-order and third-order intermodulation false signals; a local oscillator design module: and a band-pass filter is added at the output end of the local oscillator, so that the local oscillator output clutter reasonably selects the parameters of the loop filter and suppresses the phase discrimination frequency. The invention can quickly and accurately design the ultra-wide working frequency band, reduce the repeatability of the design work and improve the design efficiency.
Description
Technical Field
The invention relates to the technical field of microwave electronic circuit design, in particular to a low stray system architecture of a 100 KHz-40 GHz full-band multi-frequency conversion receiver, and particularly relates to a low stray system of a full-band receiver and a frequency conversion selection method.
Background
With the continuous expansion of wireless communication frequency spectrum, the highest working frequency band reaches millimeter waves; meanwhile, the modulation form of wireless communication is developed from common analog modulation to complex high-order digital modulation, and the modulation bandwidth reaches hundreds of megahertz. In this context, the design of the wireless receiver must also be adapted to the new operating frequency and bandwidth requirements, and especially the core specification of the receiver, the spurious-free dynamic range, becomes a significant challenge in design.
The existing radio frequency receiver is developed on the basis of a superheterodyne structure, wherein the superheterodyne structure mixes a received radio frequency signal and a local oscillator signal by utilizing nonlinearity of a device to generate an intermediate frequency signal, and then performs subsequent processing. The problems of "sensitivity" and "selectivity" often encountered in receiver design.
The superheterodyne receiver has the outstanding advantages of stable and controllable gain, high selectivity, relatively flat amplitude-frequency characteristic and easy adjustment. The disadvantage is the presence of some special disturbances, such as image disturbances, combined frequency disturbances and intermediate frequency disturbances. The method for suppressing the image interference is to improve the selectivity of the radio frequency circuit and filter the image interference as much as possible, for example, an adjustable preselection filter or a fixed preselection filter group and a local oscillator system, a broadband filter, a high and medium frequency receiver, or an image frequency suppression mixer is adopted. The receiver is usually designed using a super-heterodyne architecture in which at least one frequency conversion stage, i.e., a mixer, is present. Therefore, a lot of interference occurs in the frequency conversion process, and for the combined frequency interference of the frequency mixer, an effective frequency combination calculation algorithm is generally adopted, and the combined interference is suppressed by design methods such as local oscillator frequency selection, radio frequency signal preselection, first intermediate frequency variable and the like. The if interference is one kind of receiver interference, and in order to maintain channel consistency, the selected signal is subject to difference frequency with the local oscillator to obtain an if. But since the receiving side filter is not an ideal device, non-selected signals are also received together. If the received signal center frequency (non-selected signal) happens to be equal to the intermediate frequency, intermediate frequency interference will occur. Therefore, the method of multiple frequency conversion can effectively reduce the interference of the input signal directly fed through to the intermediate frequency port.
The more common approach is to use double conversion. And the double-conversion superheterodyne receiver is subjected to frequency conversion amplification again after the first frequency conversion amplification to form a double-conversion superheterodyne circuit. The first intermediate frequency can be selected from high intermediate frequency and low intermediate frequency, and if a high intermediate frequency mode is adopted, the suppression of mirror frequency interference and intermodulation products is facilitated. The choice of the first intermediate frequency to be high makes it possible to shift the image-disturbing signal frequency away from the useful signal frequency, so that the image frequency is greatly attenuated in the preselection filter and the high-frequency tuned amplifier. The second intermediate frequency is selected to be lower, so that the second intermediate frequency amplifier has higher gain and selectivity. The first local oscillator frequency is required to be higher than the receive frequency by a first intermediate frequency value, which must be tracked and tuned to the receive frequency as the receive frequency changes to maintain a constant first intermediate frequency, and thus a constant second local oscillator frequency.
The design of the radio frequency front end of the receiver must realize miniaturization, standardization and modularization, and in the design, the radio frequency front end is often more difficult to effectively suppress various false signals than a traditional module adopting a discrete structure, so that the design becomes a main problem to be solved in development. Due to the limitations of volume and structure, analog channels, frequency synthesis and various digital interface circuits are designed in the same module, and internal signals with large amplitude, such as local oscillator frequency, reference frequency, digital clock frequency, and the like, and harmonic components thereof are easy to generate combined interference in a receiving channel, form false response at an output end, and influence the reception of a required signal, which causes sensitivity reduction, quality deterioration, information error or loss, and even possibly causes wrong reception.
The general receiver is designed only for a specific frequency band or is designed by adopting 2-20 GHz, 20-40 GHz and other segments, and the specific signal bandwidth is not wide and is generally dozens of megahertz. In the full frequency band of 100 KHz-40 GHz, the report is not found for the ultra-wideband receiver with the signal bandwidth of 500 MHz. In such a wide operating band and signal bandwidth, the circuit and structure design of the receiver must be considered to be particularly important in order to minimize the spurious response.
The invention patent with publication number CN108540097B discloses a broadband low stray frequency conversion device, which comprises: the device comprises a segmented secondary mixing module and a segmented gain adjustable amplification filtering module; the segmented secondary mixing module is used for receiving an intermediate frequency signal, carrying out frequency conversion on the intermediate frequency signal and then sending the intermediate frequency signal to the segmented gain adjustable amplification filtering module; the segmented gain adjustable amplification filtering module is used for receiving the frequency-converted broadband signal, amplifying, filtering and adjusting the power of the frequency-converted broadband signal, and then outputting a low stray frequency conversion signal.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a low spurious system of a full-band receiver and a frequency conversion selection method.
According to the low spurious system of the full-band receiver and the frequency conversion selection method provided by the invention, the scheme is as follows:
in a first aspect, a full-band receiver low-spurious system is provided, the system including:
an intermediate frequency selection module: in a receiving frequency band, analyzing and calculating various combinations which can be formed between input signals and local oscillation signals in a frequency mixer through simulation of a computer;
a preselection filter division module: as a broadband radio frequency front end, the preselection filter reduces the chance of multiple signals entering the receiver at the same time, and reduces second-order and third-order intermodulation false signals;
a local oscillator design module: and a band-pass filter is added at the output end of the local oscillator, so that the local oscillator output clutter reasonably selects the parameters of the loop filter and suppresses the phase discrimination frequency.
Preferably, in the intermediate frequency selection module, when the intermediate frequency and the local oscillation frequency are selected, the main principle is as follows:
the selection of the first intermediate frequency is to make the image interference and the intermediate frequency interference far away from the receiving frequency band;
and the out-of-band interference is suppressed through a front-end signal preselection filter bank.
Preferably, the system further comprises a cavity structure and an electromagnetic compatibility design module: the transmission of false interference signals is blocked, a shielding box body is additionally arranged on a radio frequency analog circuit and a key strong radiation source, and a unified clock is used for various chips in the radio frequency analog circuit and the key strong radiation source.
Preferably, in the local oscillator design module, the spurious types included in the local oscillator output spectrum include: PLL fractional spur, PLL phase detection frequency leakage spur, and mutual crosstalk spur of each frequency component.
Preferably, the PLL fractional frequency spur is mainly caused by the inherent PLL fractional frequency mode, a loop filter of the PLL is designed to be 100kHz bandwidth, and a fractional spur point is recently located at an offset main frequency of 1MHz, so that the suppression is carried out through the loop filter;
the PLL phase demodulation frequency leakage stray is mainly caused by PLL phase demodulation frequency leakage, and the stray is restrained by a reasonably designed electromagnetic compatibility and loop filter;
the mutual crosstalk stray of each frequency component is mainly related to a circuit implementation form, a frequency synthesizer structure and isolation filtering among power supplies, and the design of independently dividing each local oscillator unit circuit into cavities is adopted, power supply of each local oscillator unit is respectively stabilized, and a shielding mode of a multilayer cover plate is adopted when necessary.
In a second aspect, a method for selecting low spurious frequency conversion of a full-band receiver is provided, wherein the frequency conversion selection adopts secondary or tertiary frequency conversion according to a frequency band, and the whole receiving process comprises the following steps:
step S1: selecting a current working frequency band according to the frequency of a received signal, and selecting a correct frequency channel through a frequency selection switch;
step S2: in the frequency channel, weak received signals are amplified through an amplifier, and incoherent signals and image frequencies are filtered through a band-pass filter;
step S3: for the second frequency conversion BAND2 and the third frequency conversion BAND3, first frequency mixing is carried out, and the frequency of the signals is converted into the frequency BAND of 300M-12 GHz, so that a subsequent frequency conversion circuit can be shared with the signals of the first frequency conversion BAND 1;
step S4: for the full-band 300M-40 GHz, after the first frequency conversion treatment, the frequency is converted to the frequency range of 300M-12 GHz, and the required channel is accessed to a 300M-12 GHz frequency conversion unit through a frequency selection switch for processing;
step S5: and for signals within the frequency range of 300M-12 GHz, obtaining fixed intermediate frequency output by adopting a frequency conversion process once again, and accessing a subsequent sampling circuit to complete the full-band signal receiving process.
Preferably, for a specific frequency conversion process and frequency, the received signal 100K-300M of the BAND1 will not be subjected to frequency conversion processing, but only the signal is subjected to appropriate amplitude attenuation or amplification to meet the requirements of a subsequent sampling circuit.
Preferably, the received signal 300 MHz-12 GHz of the BAND1 is divided into two sections, which are 300 MHz-8.6 GHz and 8.6 GHz-12 GHz respectively, and the 1.6GHz signal is output after 2 times of frequency conversion.
Preferably, the received signal 10 GHz-18 GHz of the BAND2 is divided into two sections, which are 10 GHz-14 GHz and 14 GHz-18 GHz respectively, and the 1.6GHz signal is output after 3 times of frequency conversion.
Preferably, the received signal 18 GHz-40 GHz of the BAND3 is divided into five sections, which are 18 GHz-22.2 GHz, 22.2 GHz-26.7 GHz, 26.7 GHz-31.2 GHz, 31.2 GHz-35.7 GHz and 35.7 GHz-40 GHz respectively, and the 1.6GHz signal is output after 3 times of frequency conversion.
Compared with the prior art, the invention has the following beneficial effects:
1. the adopted suppression technology for 3 types of stray can quickly and accurately design a modular receiver with an ultra-wide working band and a large signal bandwidth;
2. the receiver of the invention carries out system consideration in the aspect of module reuse, reduces the repeatability of design work and improves the design efficiency;
3. the multiple frequency conversion scheme adopted by the invention solves the problems of sensitivity and selectivity in the design of the receiver.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a superheterodyne receiver architecture;
FIG. 2 is a schematic diagram of a double conversion superheterodyne receiver architecture;
FIG. 3 is a block diagram of a design of a 100 kHz-12 GHz receiving channel;
FIG. 4 is a block diagram of a 10 GHz-18 GHz receive channel design;
FIG. 5 is a block diagram of the design of the 18 GHz-40 GHz receiving channel.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
An embodiment of the present invention provides a full-band receiver low-spurious system, which is shown in fig. 1 and2 and specifically includes:
fig. 2 is a schematic block diagram of the whole system, which includes the single module shown in fig. 3 and the single modules shown in fig. 4 and 5, and these 3 modules can work independently and can be combined to cover the whole frequency band according to different input frequencies. The module in fig. 3 receives 100K to 12GHz frequency, and can convert all frequencies in the frequency band to a fixed intermediate frequency, so as to facilitate subsequent signal processing. The second module in fig. 4 receives 10-18 GHz frequency, can convert all signals in the frequency band to 4-8 GHz, and then combines with the first module to complete final intermediate frequency output. The third module in fig. 4 receives 18 GHz-40 GHz frequency, can convert all signals in the frequency band to 4-8 GHz, and then combines with the third module to complete final intermediate frequency output. Therefore, if the receiving frequency is 100K-12 GHz, only one module is needed to work. If the receiving frequency is 10-18 GHz, the first module and the second module are required to work simultaneously. If the receiving frequency is 18-40 GHz, the first module and the third module are required to work simultaneously.
An intermediate frequency selection module: in the receiving frequency band, various combinations which can be formed in the mixer between the input signal and the local oscillation signal are analyzed and calculated through simulation of a computer. When selecting the intermediate frequency and the local oscillator frequency, the main principle is as follows:
the first intermediate frequency is selected such that the image interference and the intermediate frequency interference are far from the reception frequency band.
And the out-of-band interference is suppressed through a front-end signal preselection filter bank.
The receiver should be operated in a linear state when considering the gain allocation and the dynamic range, and the generation of intermodulation spurious responses can also be reduced.
A preselection filter division module: as a wideband radio frequency front end, the preselection filter reduces the chance of multiple signals entering the receiver at the same time, reducing second and third order intermodulation artifacts. For second order intermodulation, the signal can be pre-selected by using a double balanced mixer at the first conversion stage while adding a fixed or adjustable sub-octave band-pass filter at the rf input, which can attenuate the strong interfering signals in the critical band that can produce second order products at the receiver tuning frequency, and the effect of the second order intermodulation can be reduced to a negligible level. Unlike second order intermodulation, in a signal-dense environment, two strong interfering signals that fall within the passband of the pre-selector at the same time, may produce one or both of the third order intermodulation products that fall within the passband and produce unwanted spurious responses at the rf front-end receive frequency. The frequency range of the receiver affected by such interference can be reduced by using a plurality of narrow-band fixed filters to form a filter bank or by using electrically tunable filters. According to the index test of each filter, the sufficient suppression of image interference, intermediate frequency interference and second-order intermodulation can be achieved.
A local oscillator design module: and a band-pass filter is added at the output end of the local oscillator, so that the local oscillator output clutter reasonably selects the parameters of the loop filter and suppresses the phase discrimination frequency.
The local oscillator in the receiver is one of the key elements for generating false interference. The local oscillator circuit adopting the digital frequency synthesizer generally comprises circuits such as a digital frequency division circuit, a digital phase discriminator and the like, and some newly added frequency components, namely stray signals, can be generated and enter a receiving channel through a frequency mixer, or enter the receiving channel through a power line, space radiation, a printed board, and the like to generate combined interference frequency points, so that the purity of a local oscillator frequency spectrum is kept as much as possible. For the local oscillator in the radio frequency module, the mixed wiring of the digital integrated circuit and the analog circuit must be reasonable and must have good grounding and shielding measures, and a band-pass filter is added at the output end of the local oscillator when necessary, so that the output clutter of the local oscillator is as small as possible, the parameters of a loop filter are reasonably selected, and the phase discrimination frequency is suppressed.
The invention also provides a method for selecting low stray frequency conversion of a full-band receiver, wherein the frequency conversion selection adopts secondary or tertiary frequency conversion according to the frequency band, and as shown in figure 2, the whole receiving process comprises the following steps:
step S1: and selecting the current working frequency band according to the frequency of the received signal, and selecting a correct frequency channel through a frequency selection switch.
Step S2: in the frequency channel, weak received signals are amplified through an amplifier, and incoherent signals and image frequencies are filtered through a band-pass filter, so that mixing intermodulation products are prevented from being brought in during subsequent mixing, the receiving purity of the signals is guaranteed, and misjudgment is avoided.
Step S3: for the second frequency conversion BAND2 and the third frequency conversion BAND3, first frequency mixing is carried out, and the frequency of the signals is converted into the frequency BAND of 300M-12 GHz, so that the subsequent frequency conversion circuit can be shared with the signals of the first frequency conversion BAND 1.
Step S4: and for the full frequency band of 300M-40 GHz, after the first frequency conversion treatment, the frequency is converted to the frequency range of 300M-12 GHz, and the required channel is accessed to the 300M-12 GHz frequency conversion unit for processing through the frequency selection switch.
Step S5: and for signals within the frequency range of 300M-12 GHz, obtaining fixed intermediate frequency output by adopting a frequency conversion process once again, and accessing a subsequent sampling circuit to complete the full-band signal receiving process.
For a specific frequency conversion process and frequency, the following description is made:
referring to fig. 3, for received signals 100K to 300M of BAND1, frequency conversion processing is not performed, but only the signals are subjected to appropriate amplitude attenuation or amplification to meet the requirements of subsequent sampling circuits. The received signal 300 MHz-12 GHz of BAND1 is divided into two sections (300 MHz-8.6 GHz and 8.6 GHz-12 GHz) and outputs 1.6GHz signal after 2 times of frequency conversion. The first frequency conversion output intermediate frequency signals are respectively 11.2GHz and 6.5GHz, and then are mixed with a fixed local oscillator 9.6GHz or 4.9GHz to obtain 1.6GHz intermediate frequency signals. The reason for outputting two intermediate frequency signals by frequency conversion for the first time is that the image frequency signal can be far away from the received signal, and the design difficulty of the preselection filter is reduced.
Referring to FIG. 4, a received signal of BAND2 is divided into two sections (10 GHz-14 GHz and 14 GHz-18 GHz) at 10 GHz-18 GHz, and a 1.6GHz signal is output after 3 times of frequency conversion. The first frequency conversion outputs the intermediate frequency signal of 4 GHz-8 GHz, and then the intermediate frequency signal enters a (300 MHz-8.6 GHz) frequency conversion channel through the selection of a switch. The reason why the first frequency conversion outputs the 4 GHz-8 GHz intermediate frequency signal is as follows: 1. the image frequency signal can be far away from the received signal, and the design difficulty of the preselection filter is reduced. 2. The frequency conversion channels of 300MHz to 12GHz can be shared, the channel complexity is reduced, and the local oscillation number is reduced.
In fig. 5, the received signal of BAND3, 18GHz to 40GHz, is divided into 5 segments (18GHz to 22.2GHz, 22.2GHz to 26.7GHz, 26.7GHz to 31.2GHz, 31.2GHz to 35.7GHz, and 35.7GHz to 40GHz) and is frequency-converted 3 times to output a 1.6GHz signal. The first frequency conversion outputs the intermediate frequency signal of 4 GHz-8 GHz, and then the intermediate frequency signal enters a (300 MHz-8.6 GHz) frequency conversion channel through the selection of a switch. The reason why the first frequency conversion outputs the 4 GHz-8 GHz intermediate frequency signal is as follows: 1. the image frequency signal can be far away from the received signal, and the design difficulty of the preselection filter is reduced. 2. The frequency conversion channel of 300 MHz-8.6 GHz can be shared, the complexity of the channel is reduced, and the number of local oscillators is reduced.
Preselection filter division scheme:
according to the frequency calculation of the receiving channel, the following steps are obtained:
the first frequency conversion calculation of the received signal 300 MHz-12 GHz:
300MHz～8.6GHz-11.5GHz～19.8GHz＝11.2GHz
8.6GHz～12GHz-15.1GHz～18.5GHz＝6.5GHz
calculating the image frequency:
11.2GHz+11.5GHz～19.8GHz＝22.7GHz～31GHz
6.5GHz+15.1GHz～18.5GHz＝21.6GHz～25GHz
from the above calculations: the preselection filter for receiving signals of 300 MHz-12 GHz is divided into two sections:
wherein the indexes of the filter adopted in the 300 MHz-8.6 GHz frequency band are as follows:
8.9G low-pass filter, the attenuation is 80dB when the frequency is more than 10.9G;
the indexes of the filter adopted in the frequency band of 8.6 GHz-12 GHz are as follows:
the 8.3 GHz-12.4 GHz band-pass filter attenuates 80dB when the frequency is less than 6.8GHz and 70dB when the frequency is more than or equal to 15G. The image frequency can be suppressed below 70dBc by the two filters.
The receiving channel 10 GHz-18 GHz and 18 GHz-40 GHz preselection filter is divided into 5 sections (18 GHz-22.2 GHz, 22.2 GHz-26.7 GHz, 26.7 GHz-31.2 GHz, 31.2 GHz-35.7 GHz and 35.7 GHz-40 GHz).
And (3) local oscillator stray design:
in this scheme, the local oscillator output spectrum contains three types of spurs: the first is the PLL fractional spur and the second is the PLL phase detection frequency leakage spur. The third is the mutual crosstalk spurs of the frequency components.
The first type of spurs is mainly inherent in the fractional division mode of the PLL itself, which can be suppressed by the loop filter. The loop filter of the PLL in this project is designed to be 100kHz wide, and the fractional spur point falls recently at the offset of the main frequency 1MHz, so the loop filter will effectively suppress this spur. Engineering experience has shown that a loop filter designed for a 100kHz bandwidth will suppress spurs at 1MHz below-70 dBc.
The second type of spurs is mainly caused by PLL phase-detection frequency leakage. Reasonable electromagnetic compatibility design and loop filter design will effectively suppress this spurs. To effectively block the transmission of false interference signals, electromagnetic shielding is one of the most effective means, but limited by the module volume, only a shielding box body can be added to a radio frequency analog circuit and a key strong radiation source, which requires that the shielding efficiency of the box body is very high. Meanwhile, attention is paid to the power supply and wiring design of the circuit board, and the radiation channel of interference is restrained. A uniform clock should be used for the various chips within the machine.
The third category of spurs is mainly related to the circuit implementation, the frequency synthesizer structure and the isolation filtering between the power supplies. It is known from engineering experience that the mutual crosstalk between the outputs of the frequency synthesizer mainly comes from spatial induction. The division of the cells and the selection of structural shielding measures are therefore of considerable importance. In the project, the design of independent cavity division of each local oscillator unit circuit is adopted, the power supply of each unit is respectively stabilized, and a shielding mode of a multilayer cover plate is adopted when necessary.
As can be seen from the above analysis, the stray suppression requirements are guaranteed by reasonable design of the loop filter, electromagnetic compatibility design and cavity structure design, and the project local oscillator stray requirements are met.
Next, the present invention will be described in more detail.
By utilizing the design method of the patent, a circuit implementation form mainly based on a micro-assembly process is adopted, and the receiver circuits of three modules are designed, respectively correspond to the receiving channels of 100 kHz-12 GHz, 10 GHz-18 GHz and 18 GHz-40 GHz, and cover the full-band range of 100 KHz-40 GHz. The design requirement of the spurious-free dynamic range larger than 60dBc is realized. The receiver has the advantages of small volume, modular design, convenience in assembly and the like.
The implementation steps are as follows:
step 1: and according to the working mode instruction, selecting automatic full-band scanning or setting the received working frequency.
Step 2: if the scanning is automatic scanning, the processor performs frequency sweeping operation according to frequency stepping according to the operating frequency sequence of 100 kHz-40 GHz.
And step 3: if the receiving frequency is set to work, the processor automatically judges the working frequency range, so that the receiving channel of which the working frequency belongs to 100 kHz-12 GHz, 10 GHz-18 GHz and 18 GHz-40 GHz is selected.
And 4, step 4: if the working frequency is between 100kHz and 10GHz, only a receiving channel between 100kHz and 12GHz is used. When the received signal is 100 kHz-300 MHz, the signal is amplified and sorted by a straight-through channel and then is sent to a direct sampling port without frequency conversion treatment. The 300 MHz-12 GHz is divided into 2 segments (300 MHz-8.6 GHz and 8.6 GHz-12 GHz) and the 1.6GHz signal is output after 2 times of frequency conversion. The first frequency conversion output intermediate frequency signals are respectively 11.2GHz and 6.5GHz, and then are mixed with a fixed local oscillator 9.6GHz or 4.9GHz to obtain 1.6GHz intermediate frequency signals.
And 5: if the working frequency is 10 GHz-18 GHz, two receiving channels of 100 kHz-12 GHz and 10 GHz-18 GHz are needed. The input signal enters corresponding preselection filters in two sections (10 GHz-14 GHz and 10 GHz-14 GHz) according to the working frequency, and the 1.6GHz signal is output after 3 times of frequency conversion. The intermediate frequency signal IF0 is output in a frequency conversion mode in a receiving channel of 10 GHz-18 GHz and is 4 GHz-8 GHz, and then enters a receiving channel (100 kHz-10 GHz) through switch selection. And processed in channel 1 as per step 4.
Step 6: if the working frequency is 18 GHz-40 GHz, two receiving channels of 100 kHz-12 GHz and 18 GHz-40 GHz need to be used simultaneously. In the 18 GHz-40 GHz receiving channel, the input signal enters the corresponding preselection filter in 5 sections (18 GHz-22.2 GHz, 22.2 GHz-26.7 GHz, 26.7 GHz-31.2 GHz, 31.2 GHz-35.7 GHz and 35.7 GHz-40 GHz) according to the working frequency, and the 1.6GHz signal is output after 3 times of frequency conversion. The frequency conversion output intermediate frequency signal IF0 is 4 GHz-8 GHz, and then enters a frequency conversion channel (100 kHz-10 GHz) through switch selection. And processed in channel 1 as per step 4.
And 7: and each receiving channel simultaneously controls the receiving gain according to the amplitude of the signal, so that the requirement of a subsequent intermediate frequency acquisition system on the amplitude is met.
The embodiment of the invention provides a low stray system of a full-band receiver and a frequency conversion selection method, and the adopted stray suppression technology can quickly and accurately design a modular receiver with an ultra-wide working frequency band and a large signal bandwidth; the receiver in the invention carries out system consideration in the aspect of module multiplexing, reduces the repeatability of design work and improves the design efficiency.
Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, units provided by the present invention as pure computer readable program code, the system and its various devices, modules, units provided by the present invention can be fully implemented by logically programming method steps in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units included in the system for realizing various functions can also be regarded as structures in the hardware component; means, modules, units for performing the various functions may also be regarded as structures within both software modules and hardware components for performing the method.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A full-band receiver low spurious system, comprising:
an intermediate frequency selection module: in a receiving frequency band, analyzing and calculating various combinations which can be formed between input signals and local oscillation signals in a frequency mixer through simulation of a computer;
a preselection filter division module: as a broadband radio frequency front end, the preselection filter reduces the chance of multiple signals entering the receiver at the same time, and reduces second-order and third-order intermodulation false signals;
a local oscillator design module: and a band-pass filter is added at the output end of the local oscillator, so that the local oscillator output clutter reasonably selects the parameters of the loop filter and suppresses the phase discrimination frequency.
2. The system of claim 1, wherein the intermediate frequency selection module selects the intermediate frequency and the local oscillator frequency according to the following main principles:
the selection of the first intermediate frequency is to make the image interference and the intermediate frequency interference far away from the receiving frequency band;
and the out-of-band interference is suppressed through a front-end signal preselection filter bank.
3. The full-band receiver low-spurious system of claim 1, further comprising a cavity structure and an electromagnetic compatibility design module: the transmission of false interference signals is blocked, a shielding box body is additionally arranged on a radio frequency analog circuit and a key strong radiation source, and a unified clock is used for various chips in the radio frequency analog circuit and the key strong radiation source.
4. The full-band receiver low spurious system of claim 1, wherein in the local oscillator design module, the spurious species contained in the local oscillator output spectrum include: PLL fractional spur, PLL phase detection frequency leakage spur, and mutual crosstalk spur of each frequency component.
5. The full-band receiver low spur system of claim 4, wherein the PLL fractional spur is mainly due to inherent PLL fractional frequency division mode itself, and the loop filter of the PLL is designed to have a 100kHz bandwidth, and the fractional spur is located at the offset dominant frequency of 1MHz recently, so that the spur is suppressed by the loop filter;
the PLL phase demodulation frequency leakage stray is mainly caused by PLL phase demodulation frequency leakage, and the stray is restrained by a reasonably designed electromagnetic compatibility and loop filter;
the mutual crosstalk stray of each frequency component is mainly related to a circuit implementation form, a frequency synthesizer structure and isolation filtering among power supplies, and the design of independently dividing each local oscillator unit circuit into cavities is adopted, power supply of each local oscillator unit is respectively stabilized, and a shielding mode of a multilayer cover plate is adopted when necessary.
6. A method for selecting low spurious level frequency conversion of a full-band receiver, based on the low spurious level system of the full-band receiver as claimed in any one of claims 1 to 5, wherein the frequency conversion selection employs secondary or tertiary frequency conversion according to frequency band, and the whole receiving process includes:
step S1: selecting a current working frequency band according to the frequency of a received signal, and selecting a correct frequency channel through a frequency selection switch;
step S2: in the frequency channel, weak received signals are amplified through an amplifier, and incoherent signals and image frequencies are filtered through a band-pass filter;
step S3: for the second frequency conversion BAND2 and the third frequency conversion BAND3, first frequency mixing is carried out, and the frequency of the signals is converted into the frequency BAND of 300M-12 GHz, so that a subsequent frequency conversion circuit can be shared with the signals of the first frequency conversion BAND 1;
step S4: for the full-band 300M-40 GHz, after the first frequency conversion treatment, the frequency is converted to the frequency range of 300M-12 GHz, and the required channel is accessed to a 300M-12 GHz frequency conversion unit through a frequency selection switch for processing;
step S5: and for signals within the frequency range of 300M-12 GHz, obtaining fixed intermediate frequency output by adopting a frequency conversion process once again, and accessing a subsequent sampling circuit to complete the full-band signal receiving process.
7. The method of claim 6, wherein for a specific frequency conversion process and frequency, the received 100K-300M BAND1 signal is not frequency converted, but is properly amplitude attenuated or amplified to meet the requirements of a subsequent sampling circuit.
8. The method of claim 7, wherein the received signal 300 MHz-12 GHz of the BAND1 is divided into two segments, which are 300 MHz-8.6 GHz and 8.6 GHz-12 GHz, respectively, and the 1.6GHz signal is output after 2 frequency conversions.
9. The method for selecting low spurious frequency conversion of a full-BAND receiver according to claim 6, wherein the received signal 10 GHz-18 GHz of BAND2 is divided into two segments, 10 GHz-14 GHz and 14 GHz-18 GHz respectively, and after 3 times of frequency conversion, a 1.6GHz signal is output.
10. The method for selecting low-spurious frequency conversion of a full-BAND receiver according to claim 6, wherein the received signal 18 GHz-40 GHz of BAND3 is divided into five BANDs, which are respectively 18 GHz-22.2 GHz, 22.2 GHz-26.7 GHz, 26.7 GHz-31.2 GHz, 31.2 GHz-35.7 GHz and 35.7GHz, and 1.6GHz signal is output after 3 times of frequency conversion.
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