CN112422123A - Low-phase noise frequency synthesizer and local oscillator implementation method - Google Patents
Low-phase noise frequency synthesizer and local oscillator implementation method Download PDFInfo
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- CN112422123A CN112422123A CN202011330135.6A CN202011330135A CN112422123A CN 112422123 A CN112422123 A CN 112422123A CN 202011330135 A CN202011330135 A CN 202011330135A CN 112422123 A CN112422123 A CN 112422123A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
- H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/083—Details of the phase-locked loop the reference signal being additionally directly applied to the generator
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/093—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/099—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
- H03L7/0991—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider
- H03L7/0992—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider comprising a counter or a frequency divider
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Abstract
The invention belongs to the technical field of analog signal processing, and particularly relates to a low-phase noise frequency synthesizer and a local oscillator implementation method. The invention adopts a high-temperature superconducting sapphire oscillator as a reference source, a clock generated by the high-temperature superconducting sapphire oscillator as a reference clock, and a direct frequency synthesis technology and a DDS (direct digital synthesis) combined mode are adopted to synthesize a local oscillator, a second local oscillator and other clocks. The DDS is used for compensating the frequency error of the sapphire oscillator, expanding a local oscillator to a plurality of frequency points and realizing frequency agility. The invention reserves a crystal oscillator reference source, generates a reference clock close to the sapphire oscillator by a direct frequency synthesis mode, and is reserved before the sapphire oscillator is started. The invention can improve the phase noise.
Description
Technical Field
The invention belongs to the technical field of analog signal processing, and particularly relates to a low-phase noise frequency synthesizer and a local oscillator implementation method.
Background
The frequency synthesizer is used for providing coherent first local oscillator, second local oscillator and other required various clocks for the radar system. The synthesized local oscillator and each clock are required to have low phase noise, and one local oscillator has a plurality of frequency points and can rapidly hop frequency.
The basic working principle of the frequency synthesizer is as follows: the reference source generates a reference clock, the power is divided into multiple paths, and a local oscillator, a two-local oscillator and other clocks are synthesized by adopting synthesis modes such as direct frequency synthesis and phase-locked loops respectively. The selection of the reference source and the frequency synthesis method determines the phase noise and the frequency hopping time of the synthesized local oscillator.
At present, a low-phase noise constant-temperature crystal oscillator is mainly used as a reference source, and a local oscillator and other clocks are synthesized in a direct frequency synthesis mode. The phase noise will be at least 20log (n) worse during the frequency synthesis, while the amplifier, frequency multiplier and harmonic generator will generate additional phase noise during this process, which will affect the phase noise of the synthesized local oscillator. Due to the existence of thermal noise, the phase noise performance of the constant temperature crystal oscillator is difficult to further improve, so that the phase noise of a synthesized local oscillator is difficult to further improve.
The high-temperature superconducting sapphire oscillator directly generates a reference clock with the frequency close to the local oscillator frequency, frequency multiplication is not needed in the process of synthesizing the local oscillator, the deterioration of 20log (N) of phase noise is avoided, and compared with the constant-temperature crystal oscillator with low phase noise, the phase noise of the local oscillator can be obviously improved.
The disadvantage of high temperature superconducting sapphire oscillators is mainly the start-up time. The sapphire oscillator is arranged in the low-temperature Dewar, after the temperature is reduced to a superconducting temperature region, oscillation can be started to generate reference clock output, and the time for the refrigerator to degrade the temperature of the low-temperature Dewar from normal temperature to the superconducting temperature region is the oscillation starting time which generally needs 40-60 min. In addition, the processing errors of sapphire and the size of the resonator can cause the error of the output frequency, namely frequency offset, and under the current processing precision, the error is in the range of +/-1%, and frequency compensation is needed.
Disclosure of Invention
Aiming at the defects of the background art, the invention provides a low-phase noise frequency synthesizer and an implementation method thereof, compared with a direct frequency synthesis method adopting a low-phase noise constant-temperature crystal oscillator as a reference source, the phase noise of a local oscillator can be improved by more than 10 dB.
The invention adopts a high-temperature superconducting sapphire oscillator as a reference source, a clock generated by the high-temperature superconducting sapphire oscillator as a reference clock, and a direct frequency synthesis technology and a DDS (direct digital synthesis) combined mode are adopted to synthesize a local oscillator, a second local oscillator and other clocks. The DDS is used for compensating the frequency error of the sapphire oscillator, expanding a local oscillator to a plurality of frequency points and realizing frequency agility. The invention reserves a crystal oscillator reference source, generates a reference clock close to the sapphire oscillator by a direct frequency synthesis mode, and is reserved before the sapphire oscillator is started.
The invention has the beneficial effects that: compared with the scheme that a constant-temperature crystal oscillator with low phase noise is used as a reference source and a direct frequency synthesis technology is adopted, the phase noise of a synthesized local oscillator is improved by about 10 dB; compensating the frequency deviation of the sapphire oscillator by adopting a direct frequency synthesis technology combined with a DDS technology, expanding a local oscillator to a broadband and multi-frequency point, and carrying out frequency agile; the constant-temperature crystal oscillator with low phase noise is adopted to synthesize a clock with the same frequency as a reference source through a frequency doubling and harmonic generator, and the clock is switched through a microwave switch according to the working state of the sapphire oscillator to be reserved before the temperature of the sapphire oscillator is reduced to a superconducting temperature region. Each frequency synthesis circuit is provided with a DDS module, and each DDS module is provided with two groups of frequency control words, so that the frequency compensation of the low-temperature oscillation circuit is completed.
Drawings
Fig. 1 is a schematic block diagram of a frequency synthesizer of the present invention (not related to the main control unit portion).
Fig. 2 is a schematic block diagram of a frequency synthesizer of the present invention involving only a main control unit.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
As shown in fig. 1 and fig. 2, a multi-frequency point, frequency agility, low phase noise frequency synthesizer includes a low temperature oscillation circuit, a normal temperature oscillation circuit, a main control unit, a microwave switch, a first power divider, a first local oscillation frequency synthesis circuit, a DDS circuit, and a second local oscillation frequency synthesis circuit. The main control unit collects the temperature of the low-temperature Dewar and the voltage output by the detector in the low-temperature oscillation circuit, thereby controlling the running states of the microwave switch and the constant-temperature crystal oscillator. The outputs of the low-temperature oscillation circuit and the normal-temperature oscillation circuit are connected with a microwave switch, the microwave switch is connected with a power divider, and the output of the power divider I is respectively connected with a local oscillation frequency synthesis circuit, a DDS circuit and a two-local oscillation frequency synthesis circuit.
When the device is started, the main control unit controls the microwave switch to be connected with the normal-temperature oscillation circuit and input into the first power divider. When the temperature sampled by the main control unit is lower than a set value and the voltage output by the detector is greater than the set value, the main control unit controls the microwave switch to be switched to the low-temperature oscillation circuit to input the first power divider and controls the crystal oscillator switch to turn off the constant-temperature crystal oscillator.
The low-temperature oscillation circuit comprises a sapphire oscillator, a coupler and a detector. The output of the sapphire oscillator is connected with the input of the coupler, the output of the coupler is respectively connected with the microwave switch and the detector, and the output of the detector is connected with the main control unit. The sapphire oscillator and the temperature sensor are placed in a low-temperature Dewar, wherein the temperature sensor is tightly attached to the cavity wall of the sapphire oscillator.
The normal temperature oscillation circuit comprises a constant temperature crystal oscillator, a frequency multiplier, a low noise amplifier, a harmonic generator and a first band-pass filter. The output of the constant temperature crystal oscillator is connected with the input of a frequency multiplier, the output of the frequency multiplier is connected with the input of a low noise amplifier, the output of the low noise amplifier is connected with the input of a harmonic generator, the output of the harmonic generator is connected with the input of a band-pass filter, and the output of the band-pass filter is connected with a microwave switch. According to the invention, a first band-pass filter is designed according to the output frequency of the low-temperature oscillating circuit, so that the harmonic nearest to the output frequency of the low-temperature oscillating circuit is filtered out, and the error of the output frequencies of the normal-temperature oscillating circuit and the low-temperature oscillating circuit is less than +/-100 MHz.
The DDS circuit comprises an amplifier III, a frequency divider I, a band-pass filter II, a power divider II, a DDS module I, a DDS module II and a DDS module III. The input of the third amplifier is connected with the output of the first power divider, the output of the third amplifier is connected with the input of the first frequency divider, the output of the first frequency divider is connected with the input of the second band-pass filter, the output of the second band-pass filter is connected with the input of the second power divider, and the output of the second power divider is respectively connected with the inputs of the DDS module I, the DDS module II and the DDS module III. And the first frequency divider divides the frequency of the reference clock output by the normal-temperature oscillation circuit or the low-temperature oscillation circuit to about 3.6GHz and is used as a reference clock of the DDS module I, the DDS module II and the DDS module III. The DDS module I, the DDS module II and the DDS module III are used for tuning word output frequency according to the frequency sent by the main control unit, and when the reference clock is 3.6GHz, the output frequency precision is about 0.84 Hz. Therefore, the DDS module I, the DDS module II and the DDS module III can change the output frequency according to the externally input command, so that the first local oscillator, the system clock and the second local oscillator frequency are convenient to change, the precision is ensured, and the DDS module I, the DDS module II and the DDS module III are suitable for the universal design of products of different models. If the system clock required by a certain product is 100Mhz, and the system clock of another product is 150Mhz, only the frequency tuning word sent by the main control unit to the DDS module II is changed when different products are designed, and the universality of the invention is greatly improved.
A local oscillator frequency synthesis circuit comprises a first amplifier, a first filter bank, a first mixer, a second filter bank and a second amplifier. The input of the first amplifier is connected with the output of the first power divider, the input of the first filter bank is connected with the DDS circuit, the output of the first amplifier and the output of the first filter bank are connected with the input of the first mixer, the output of the first mixer is connected with the input of the second filter bank, and the output of the second filter bank is connected with the input of the second amplifier. The output frequency of the DDS module I is changed by the main control unit according to the frequency tuning word compiled by the frequency code, and the filter bank I and the filter bank II are controlled by the main control unit and synchronously switched along with the change of the output frequency of the DDS module I. Therefore, the local oscillator frequency synthesis circuit can flexibly change a local oscillator frequency according to an externally input frequency code, realizes multi-frequency point frequency agility, and has a simple circuit structure.
The frequency hopping time of the first local oscillator is determined by the time of the main control unit for compiling the frequency code, the time of the DDS module I for generating the waveform according to the frequency tuning word, the microwave switch switching time of the first filter bank and the second filter bank and the delay time of the first filter bank and the second filter bank. The time for the master control unit to compile the frequency code is about 400 ns. And after receiving the frequency tuning word, the DDS module I generates waveform output with corresponding frequency, and the required time is less than 500 ns. The switching time of the microwave switch is less than 100 ns. The delay time of the filter is less than 100 ns. The DDS module I generates output waveforms and switches microwave switches of the filter group I and the filter group II at the same time, and the total frequency hopping time of the local oscillator is less than 1.1 mu s, while the frequency agility time of the conventional phase-locked loop is more than hundreds of mu s.
The main control unit presets two groups of frequency tuning words for the DDS module I according to the output frequencies of the normal-temperature oscillating circuit and the low-temperature oscillating circuit, synchronous switching is carried out when a microwave switch is switched, the frequency difference between the normal-temperature oscillating circuit and the low-temperature oscillating circuit is compensated, the frequency of a synthesized local oscillator at the same frequency point is kept consistent, therefore, frequency compensation of two working modes is realized through a simpler circuit, and the circuit is simplified. Because the output frequency precision of the DDS module I can reach about 0.84Hz, the frequency precision of a local oscillator can reach less than 1Hz both in the normal-temperature oscillating circuit and the low-temperature oscillating circuit. The frequency range of a local oscillator is 5 GHz-8 GHz, corresponding frequency tuning words are set according to the requirements of different models of products, and a local oscillator with the required frequency is synthesized.
The second local oscillator frequency synthesis circuit comprises an amplifier IV, a frequency divider II, a band-pass filter IV, a mixer II, a band-pass filter III, a band-pass filter V and an amplifier V. The input of the fourth amplifier is connected with the output of the first power divider, the output of the fourth amplifier is connected with the input of the second frequency divider, the output of the second frequency divider is connected with the input of the fourth band-pass filter, the third band-pass filter is connected with the output of the DDS module III, the output of the fourth band-pass filter and the output of the third band-pass filter are connected with the input of the second mixer, the output of the second mixer is connected with the input of the fifth band-pass filter, and the output of the fifth band-pass filter is connected with the input of the fifth amplifier. The main control unit sets two groups of frequency tuning words according to the output frequencies of the normal-temperature oscillation circuit and the low-temperature oscillation circuit, synchronously switches when the microwave switch is switched, compensates the frequency difference between the normal-temperature oscillation circuit and the low-temperature oscillation circuit, and enables the frequencies of the synthesized two local oscillators to be consistent, and the error is less than 1 Hz. The frequency range of the two local oscillators is generally between 1GHz and 3GHz,
the main control unit of the invention takes FPGA as a core and has the main functions as follows: collecting data input by a temperature sensor and a detector to judge the working state of the sapphire oscillator, judging that the sapphire oscillator is normally started when the sampled temperature is lower than a set value and the voltage output by the detector is greater than the set value, controlling a microwave switch to be switched to the output of the sapphire oscillator, and closing a switch of a constant-temperature crystal oscillator; the frequency codes are compiled into frequency tuning words of the DDS module I and control commands of the filter bank I and the filter bank II, the DDS module I is controlled to output the frequency corresponding to the frequency codes, and the filter bank I and the filter bank II are controlled to switch internal filters, so that a local oscillation frequency synthesis circuit is controlled to output the frequency corresponding to the frequency codes; and pre-storing frequency tuning words of the DDS module II and the DDS module III according to the output frequency of the low-temperature oscillation circuit and the output frequency of the normal-temperature oscillation circuit, and synchronously switching with the microwave switch. The input of the main control unit is connected with the output of the temperature sensor, the output of the detector and the frequency code of external input, and the output of the main control unit is connected with the input of the filter bank I, the input of the filter bank II, the input of the DDS module I, the input of the DDS module II and the input of the DDS module III.
A method for realizing a low phase noise local oscillator is characterized by comprising the following steps:
the method comprises the following steps: after the frequency synthesizer is started, the normal-temperature oscillation circuit generates a reference clock, and the reference clock is output to the first power divider after passing through the microwave switch. And meanwhile, a refrigeration system of the low-temperature Dewar is started, the master control unit collects temperature data transmitted by a temperature sensor in the low-temperature Dewar and voltage output by the detector in real time, and the working state of the low-temperature oscillation circuit is comprehensively judged. After the low-temperature oscillation circuit works normally, the main control unit sends a control command to control the microwave switch to be switched to the low-temperature oscillation circuit for output, and meanwhile, the switch of the constant-temperature crystal oscillator in the normal-temperature oscillation circuit is closed.
Step two: the reference clock output from the microwave switch is divided into three paths in the first power divider, and the three paths are respectively output to a local oscillation frequency synthesis circuit, a DDS circuit and a second local oscillation frequency synthesis circuit.
Step three: a reference clock output from the first power divider to the DDS circuit is amplified by the third amplifier, frequency is divided into three paths by a frequency divider to reach the range of 3.0 GHz-4.0 GHz, and after harmonic is filtered by the second band-pass filter, the power is divided into three paths which are respectively output to the DDS module I, the DDS module II and the DDS module III;
step four: the DDS module I generates a dot frequency clock with a wide frequency band and a plurality of frequency points according to frequency harmonic words sent by the main control unit, the dot frequency clock is filtered by the first band-pass filter bank, then mixed with the first path of reference clock output by the first power divider in the first frequency mixer, filtered by the second band-pass filter bank and amplified by the second amplifier, and a local oscillator output is generated;
step five: the DDS module II generates dot frequency which is used as a system clock of the radar, and the general frequency range of the DDS module II is 40 MHz-200 MHz. In the debugging process, according to the frequency of a reference clock, adjusting a frequency tuning word and controlling the frequency of a system clock to be within a required error range;
step six: and a third path of reference clock output by the fourth amplifier is subjected to frequency division to an interval range of 1.0 GHz-2.0 GHz by using a frequency divider, harmonic waves and noise are filtered by a band-pass filter IV, and then the third path of reference clock is mixed with a single-frequency continuous wave generated by a DDS module III according to the frequency harmonic words sent by the main control unit in a second mixer. And filtering by a band-pass filter V, and amplifying by an amplifier V to generate two local oscillator outputs. In the debugging process, according to the frequency of the reference clock, the frequency tuning word is adjusted, the output frequency of the DDS module III is controlled, and the frequency of the two local oscillators is within the required error range.
When the normal-temperature oscillation circuit works, the phase noise of 1kHz is about-122 dBc/Hz; when the low-temperature oscillation circuit works, the phase noise of 1kHz is about-132 dBc/Hz. Therefore, the phase noise of the device of the invention is equivalent to that of a frequency synthesizer based on a constant temperature crystal oscillator only in a short time during starting, and the phase noise is very low during normal operation. The device and the method are suitable for the radar system with higher requirements on phase noise and improvement factors.
Claims (10)
1. The utility model provides a low phase noise frequency synthesizer, includes low temperature oscillation circuit, normal atmospheric temperature oscillation circuit, the main control unit, microwave switch, the merit divides the ware one, a local oscillator frequency synthetic circuit, DDS circuit and two local oscillator frequency synthetic circuits, low temperature oscillation circuit, normal atmospheric temperature oscillation circuit's output and microwave switch are connected, microwave switch divides the ware one with the merit to be connected, the output that the ware was divided to the merit is connected with a local oscillator frequency synthetic circuit, DDS circuit and two local oscillator frequency synthetic circuits respectively, its characterized in that: the DDS circuit comprises a third amplifier, a first frequency divider, a second band-pass filter, a second power divider, a first DDS module I, a second DDS module II and a third DDS module, wherein the input of the third amplifier is connected with the output of the first power divider, the output of the third amplifier is connected with the input of the first frequency divider, the output of the first frequency divider is connected with the input of the second band-pass filter, the output of the second band-pass filter is connected with the input of the second power divider, and the output of the second power divider is respectively connected with the inputs of the first DDS module I, the second DDS module II and the third DDS module; the DDS module I, the DDS module II and the DDS module III tune word output frequency according to the frequency sent by the main control unit; the main control unit collects data input by the temperature sensor and the detector to judge the working state of the sapphire oscillator, and when the sampled temperature is lower than a set value and the voltage output by the detector is greater than the set value, the sapphire oscillator is judged to be normally started, a microwave switch is controlled to be switched to the output of the sapphire oscillator, and the switch of the constant temperature crystal oscillator is closed; the frequency codes are compiled into frequency tuning words of the DDS module I and control commands of the filter bank I and the filter bank II, the DDS module I is controlled to output the frequency corresponding to the frequency codes, and the filter bank I and the filter bank II are controlled to switch internal filters, so that a local oscillation frequency synthesis circuit is controlled to output the frequency corresponding to the frequency codes; and pre-storing frequency tuning words of the DDS module II and the DDS module III according to the output frequency of the low-temperature oscillation circuit and the output frequency of the normal-temperature oscillation circuit, and synchronously switching with the microwave switch.
2. A low phase noise frequency synthesizer as defined in claim 1, wherein: the input of the main control unit is connected with the output of the temperature sensor, the output of the detector and the frequency code of external input, and the output of the main control unit is connected with the input of the filter bank I and the filter bank II, the input of the DDS module I, the input of the DDS module II and the input of the DDS module III.
3. A low phase noise frequency synthesizer as defined in claim 1, wherein: the low-temperature oscillation circuit comprises a sapphire oscillator, a coupler and a detector, wherein the output of the sapphire oscillator is connected with the input of the coupler, the output of the coupler is respectively connected with a microwave switch and the detector, the output of the detector is connected with a main control unit, and the sapphire oscillator and a temperature sensor are placed in a low-temperature Dewar.
4. A low phase noise frequency synthesizer as defined in claim 1, wherein: the temperature sensor is closely arranged on the cavity wall of the sapphire oscillator.
5. A low phase noise frequency synthesizer as defined in claim 1, wherein: the constant-temperature oscillation circuit comprises a constant-temperature crystal oscillator, a frequency multiplier, a low-noise amplifier, a harmonic generator and a first band-pass filter, wherein the output of the constant-temperature crystal oscillator is connected with the input of the frequency multiplier, the output of the frequency multiplier is connected with the input of the low-noise amplifier, the output of the low-noise amplifier is connected with the input of the harmonic generator, the output of the harmonic generator is connected with the input of the first band-pass filter, and the output of the first band-pass filter is connected.
6. A low phase noise frequency synthesizer as defined in claim 1, wherein: the local oscillator frequency synthesis circuit comprises a first amplifier, a first filter bank, a first mixer, a second filter bank and a second amplifier, wherein the input of the first amplifier is connected with the output of the first power divider, the input of the first filter bank is connected with the DDS circuit, the output of the first amplifier and the output of the first filter bank are connected with the input of the first mixer, the output of the first mixer is connected with the input of the second filter bank, the output of the second filter bank is connected with the input of the second amplifier, the output frequency of the DDS module I is changed by a main control unit according to frequency tuning words compiled by frequency codes, the first filter bank and the second filter bank are controlled by the main control unit, and the first filter bank and the second filter bank are synchronously switched along with the change of the output frequency of.
7. A low phase noise frequency synthesizer as defined in claim 1, wherein: the second local oscillator frequency synthesis circuit comprises an amplifier IV, a frequency divider II, a band-pass filter IV, a mixer II, a band-pass filter III, a band-pass filter V and an amplifier V, wherein the input of the amplifier IV is connected with the output of the power divider I, the output of the amplifier IV is connected with the input of the frequency divider II, the output of the frequency divider II is connected with the input of the band-pass filter IV, the output of the band-pass filter III is connected with the output of the DDS module III, the output of the band-pass filter IV and the output of the band-pass filter III are connected with the input of the mixer II, the output of the mixer II is connected with the input of the band-pass filter V, and the output of the band.
8. A method for realizing a low phase noise local oscillator is characterized in that: the method comprises the following steps:
the method comprises the following steps: after the low-temperature oscillating circuit works normally, the main control unit sends a control command to control the microwave switch to be switched to the low-temperature oscillating circuit for outputting, and simultaneously, the constant-temperature crystal oscillator in the normal-temperature oscillating circuit is switched off;
step two: the reference clock output from the microwave switch is divided into three paths in the first power divider, and the three paths are respectively output to a local oscillation frequency synthesis circuit, a DDS circuit and a second local oscillation frequency synthesis circuit;
step three: a reference clock output from the first power divider to the DDS circuit is amplified by the third amplifier, subjected to frequency division by the frequency divider, subjected to harmonic filtering by the second band-pass filter, divided into three paths and respectively output to the DDS module I, the DDS module II and the DDS module III;
step four: the DDS module I generates a dot frequency clock with a wide frequency band and a plurality of frequency points according to frequency harmonic words sent by the main control unit, the dot frequency clock is filtered by the first band-pass filter bank, then mixed with the first path of reference clock output by the first power divider in the first frequency mixer, filtered by the second band-pass filter bank and amplified by the second amplifier, and a local oscillator output is generated;
step five: the DDS module II generates dot frequency which is used as a system clock of the radar;
step six: and a third path of reference clock output by the amplifier IV is subjected to frequency division by the frequency divider IV, harmonic waves and noise waves are filtered by the band-pass filter IV, and then mixed with a single-frequency continuous wave generated by the DDS module III according to the frequency harmonic words sent by the main control unit in the frequency mixer II, filtered by the band-pass filter V, and amplified by the amplifier V to generate a second local oscillator output.
9. The method for implementing a low phase noise local oscillator according to claim 8, wherein: in the third step, the frequency range of the frequency divider after frequency division is 3.0 GHz-4.0 GHz.
10. The method for implementing a low phase noise local oscillator according to claim 8, wherein: and in the fifth step, the dot frequency range generated by the DDS module II is 40 MHz-200 MHz.
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| CN115842549A (en) * | 2023-02-15 | 2023-03-24 | 成都天锐星通科技有限公司 | Frequency synthesizer |
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