Wideband ultra-low phase noise frequency source

Abstract

The present invention provides a wide-band ultra-low phase noise frequency source, which relates to the technical field of frequency sources, and includes a first branch circuit, a second branch circuit and a phase-locked loop circuit, wherein: the first branch circuit is used to perform frequency multiplication and filtering and amplification processing on a received low phase noise reference signal to obtain a first reference signal, and the first reference signal is input into a direct digital frequency synthesizer to obtain a second reference signal; the second branch circuit is used to input the received low phase noise reference signal into a continuous spectrum generator and an ultra-narrowband electrically adjustable bandpass filter in sequence to obtain a local oscillator drive signal; the phase-locked loop circuit is used to compare the generated intermediate frequency signal with the second reference signal after receiving the local oscillator drive signal, and generate a target frequency signal according to the obtained error control signal. The present invention realizes the requirements of ultra-low phase noise and broadband, has higher frequency resolution, and makes the generated signal have lower phase noise, high clutter suppression and wide frequency range.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency sources, and in particular to a wide-band ultra-low phase noise frequency source. Background Art

[0002] With the development of technologies such as digital communication and radar, the performance requirements for broadband frequency sources are becoming increasingly higher.

[0003] At present, broadband frequency sources are mainly realized by phase-locked loop or frequency doubling filtering. However, although the existing phase-locked loop solution has good spurious indicators, the phase noise is significantly deteriorated; although the existing frequency doubling filtering method has good near-end phase noise, the far-end phase noise is significantly deteriorated. At the same time, the spurious, frequency step and frequency bandwidth of the existing broadband frequency source cannot meet the current performance requirements.

[0004] Therefore, there is an urgent need for a wide-bandwidth ultra-low phase noise frequency source to solve the above problems. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a wide-band ultra-low phase noise frequency source.

[0006] The present invention provides a wide-band ultra-low phase noise frequency source, comprising a first branch circuit, a second branch circuit and a phase-locked loop circuit, wherein:

[0007] The first branch circuit includes a direct digital frequency synthesizer, which is used to perform frequency multiplication and filtering and amplification processing on the received low phase noise reference signal to obtain a first reference signal, and input the first reference signal into the direct digital frequency synthesizer to obtain a second reference signal;

[0008] The second branch circuit includes a continuous spectrum generator and an ultra-narrowband electrically tunable bandpass filter, and is used to sequentially input the received low phase noise reference signal to the continuous spectrum generator and the ultra-narrowband electrically tunable bandpass filter to obtain a local oscillator driving signal required by the mixer in the phase-locked loop circuit;

[0009] The phase-locked loop circuit includes a phase detector, a YIG tuning oscillator and the mixer. The mixer is used to input the generated intermediate frequency signal into the phase detector after receiving the local oscillator driving signal; the phase detector is used to compare the intermediate frequency signal with the second reference signal and generate a corresponding error control signal according to the comparison result; the YIG tuning oscillator is used to generate a target frequency signal according to the error control signal.

[0010] According to a broadband ultra-low phase noise frequency source provided by the present invention, the broadband ultra-low phase noise frequency source also includes an ultra-low phase noise reference source, wherein:

[0011] The ultra-low phase noise reference source includes a power divider, and the ultra-low phase noise reference source is used to input the generated low phase noise signal into the power divider for branching processing to obtain two paths of the low phase noise reference signal, and input one of the low phase noise reference signals into the first branch circuit, and input the other low phase noise reference signal into the second branch circuit.

[0012] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the first branch circuit further includes a first amplifier, a first frequency multiplier, a first bandpass filter, a second amplifier and a second bandpass filter, wherein:

[0013] The input end of the first amplifier is connected to the first output end of the power divider, the output end of the first amplifier is connected to the input end of the first frequency multiplier, the output end of the first frequency multiplier is connected to the input end of the first band-pass filter, the output end of the first band-pass filter is connected to the input end of the second amplifier, the output end of the second amplifier is connected to the input end of the direct digital frequency synthesizer, the output end of the direct digital frequency synthesizer is connected to the input end of the second band-pass filter, and the output end of the second band-pass filter is connected to the first input end of the phase detector in the phase-locked loop circuit;

[0014] When near-end spurs exist at the target frequency point output by the direct digital frequency synthesizer, the direct digital frequency synthesizer suppresses the near-end spurs according to the received compensation data to reduce the spurs of the output signal to 95 dBc.

[0015] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the second branch circuit includes a third amplifier, a second frequency multiplier, a third bandpass filter, a fourth amplifier, a fifth amplifier, a sixth amplifier and an attenuator, wherein:

[0016] The input end of the third amplifier is connected to the second output end of the power divider, the output end of the third amplifier is connected to the input end of the second frequency multiplier, the output end of the second frequency multiplier is connected to the input end of the third bandpass filter, the output end of the third bandpass filter is connected to the input end of the fourth amplifier, the output end of the fourth amplifier is connected to the input end of the continuous spectrum generator, the output end of the continuous spectrum generator is connected to the input end of the fifth amplifier, the output end of the fifth amplifier is connected to the input end of the ultra-narrowband electrically tunable bandpass filter, the output end of the ultra-narrowband electrically tunable bandpass filter is connected to the input end of the sixth amplifier, the output end of the sixth amplifier is connected to the input end of the attenuator, and the output end of the attenuator is connected to the first input end of the mixer in the phase-locked loop circuit.

[0017] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the phase-locked loop circuit includes a loop filter, a power divider / coupler, a seventh amplifier, an intermediate frequency filter and an eighth amplifier, wherein:

[0018] The output end of the phase detector is connected to the input end of the loop filter, the output end of the loop filter is connected to the input end of the YIG tuning oscillator, the output end of the YIG tuning oscillator is connected to the input end of the power divider / coupler, the first output end of the power divider / coupler is connected to the input end of the seventh amplifier, the second output end of the power divider / coupler outputs a radio frequency signal, the output end of the seventh amplifier is connected to the second input end of the mixer, the output end of the mixer is connected to the input end of the intermediate frequency filter, the output end of the intermediate frequency filter is connected to the input end of the eighth amplifier, and the output end of the eighth amplifier is connected to the second input end of the phase detector;

[0019] Wherein, when the direct digital frequency synthesizer generates far-end spurious, the loop filter and the intermediate frequency filter filter out the far-end spurious to reduce the generated spurious to 95 dBc;

[0020] The ultra-narrowband electrically tunable bandpass filter is further used to filter out interference signals other than the target signal in the multi-carrier signal generated by the continuous spectrum generator, wherein the target signal is the signal in the multi-carrier signal that forms the local oscillator drive signal;

[0021] The mixer, the seventh amplifier and the power divider / coupler form a reverse isolation circuit for suppressing spurious signals generated by the interference signal.

[0022] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the output frequency of the ultra-low phase noise reference source is 100 MHz, and the phase noise of the ultra-low phase noise reference source meets the following condition: -180 dBc@10 kHz.

[0023] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the phase noise of the YIG tuned oscillator meets the following conditions: -150dBc / Hz@1MHz or -167dBc / Hz@10MHz.

[0024] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the continuous spectrum generator is an equally spaced continuous spectrum generator. When the output frequency interval of the equally spaced continuous spectrum generator is 200MHz and the carrier frequency is 10GHz, the phase noise of the equally spaced continuous spectrum generator meets the following conditions: -138dBc / Hz@10kHz.

[0025] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the ultra-narrowband electrically tunable bandpass filter satisfies the following conditions: the relative bandwidth of the ultra-narrowband electrically tunable bandpass filter is less than or equal to 0.5%, and the corresponding bandwidth when the signal attenuation reaches 85dB is less than or equal to 100MHz, and the corresponding bandwidth when the signal attenuation reaches 100dB is less than or equal to 200MHz.

[0026] According to a wide-band ultra-low phase noise frequency source provided by the present invention, the output frequency range of the direct digital frequency synthesizer is 100 MHz to 200 MHz, and the frequency step is 0.1 mHz.

[0027] The broadband ultra-low phase noise frequency source provided by the present invention combines a phase-locked loop with a frequency multiplier to achieve the requirements of ultra-low phase noise and broadband, and has higher frequency resolution, so that the generated signal has lower phase noise, high clutter suppression and a wide frequency range. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is a schematic structural diagram of the wide-band ultra-low phase noise frequency source provided by the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The existing phase-locked loop circuit has a relatively high noise floor due to the frequency multiplication factor, and cannot achieve ultra-low phase noise. To address this problem, the present invention adopts a frequency shift phase-locked loop, fixes the frequency multiplication factor N of the phase-locked loop to 1, thereby reducing the noise floor of the phase-locked loop circuit itself; at the same time, the output frequency is shifted to a very low frequency band in the present invention, so that the phase detection works at a lower frequency, further reducing the noise floor of the phase-locked loop.

[0032] In order to solve the problem that the existing mixing phase-locked loop has a large number of frequency conversions, resulting in a lot of noise and spurious introduction, the frequency offset phase-locked loop with a wide-band ultra-low phase noise frequency source provided by the present invention has only one frequency conversion, so that the introduced noise and spurious introduction are small, further improving the noise of the frequency source and improving spurious suppression.

[0033] Figure 1 The schematic diagram of the structure of the broadband ultra-low phase noise frequency source provided by the present invention is as follows: Figure 1 As shown, the present invention provides a wide-band ultra-low phase noise frequency source, including a first branch circuit 101, a second branch circuit 102 and a phase-locked loop circuit 103, wherein:

[0034] The first branch circuit 101 includes a direct digital frequency synthesizer (DDS) 1011, which is used to perform frequency multiplication and filtering and amplification processing on the received low phase noise reference signal to obtain a first reference signal, and input the first reference signal to the direct digital frequency synthesizer 1011 to obtain a second reference signal;

[0035] The second branch circuit 102 includes a continuous spectrum generator 1021 and an ultra-narrowband electrically tunable bandpass filter 1022, and is used to sequentially input the received low phase noise reference signal to the continuous spectrum generator 1021 and the ultra-narrowband electrically tunable bandpass filter 1022 to obtain a local oscillator driving signal required by the mixer 1033 in the phase-locked loop circuit 103;

[0036] The phase-locked loop circuit 103 includes a phase detector 1031, a YIG (single crystal yttrium iron garnet) tuning oscillator 1032 and the mixer 1033. The mixer 1033 is used to input the generated intermediate frequency signal into the phase detector 1031 after receiving the local oscillator driving signal; the phase detector 1031 is used to compare the intermediate frequency signal with the second reference signal and generate a corresponding error control signal according to the comparison result; the YIG tuning oscillator 1032 is used to generate a target frequency signal according to the error control signal.

[0037] In the present invention, the first branch circuit 101 receives a reference signal with low phase noise, then performs frequency multiplication on the reference signal, performs spurious suppression and noise shaping through a digital filter, and outputs a high-quality first reference signal. Then, the first reference signal is processed by utilizing the high frequency resolution and fast switching capability of the direct digital frequency synthesizer 1011 to generate a second reference signal as a reference signal for the phase-locked loop circuit 103.

[0038] In the present invention, the second branch circuit 102 receives the same low phase noise reference signal and generates a wide-band, equally spaced spectrum output, thereby providing a stable local oscillator signal source for the mixer in the phase-locked loop. The signal source needs to have low phase noise and precise frequency control capabilities. The ultra-narrowband electrically tunable bandpass filter 1022 is connected after the continuous spectrum generator 1021. Specifically, refer to Figure 1 As shown, the reference signal with low phase noise enters the continuous spectrum generator 1021 after being amplified, and then the generated equally spaced continuous spectrum signal is input into the fifth amplifier 1027 to prevent the signal amplitude from being too small and thus deteriorating the far-end phase noise. After the signal amplified by the fifth amplifier 1027 is input into the ultra-narrowband electrically tunable bandpass filter 1022, the ultra-narrowband electrically tunable bandpass filter 1022 outputs a single-point frequency signal corresponding to the final output frequency. In the present invention, the frequency selection of the ultra-narrowband electrically tunable bandpass filter 1022 can be automatically calculated according to the output frequency by the high-speed controller 105; finally, the single-point frequency signal is sequentially input into the mixer 1033 in the phase-locked loop circuit 103 through the sixth amplifier 1028 and the attenuator 1029 as the local oscillator driving signal of the mixer 1033. In the present invention, by finely adjusting the ultra-narrowband electrically tunable bandpass filter 1022, it is possible to ensure that interference outside the 100M bandwidth of the filter is suppressed by more than 85dBc, and interference outside the 200M bandwidth of the filter is suppressed by more than 100dBc, thereby effectively suppressing other noise and spurious signals, retaining only the required local oscillator signal, ensuring that the final output spurious signal of the RF signal is lower than 95dBc, and improving the spurious signal of the frequency source.

[0039] In the present invention, the mixer 1033 performs mixing based on the local oscillator driving signal from the second branch circuit 102 to generate a mixed intermediate frequency signal. The phase detector 1031 is responsible for comparing the phase difference between the second reference signal from the direct digital frequency synthesizer 1011 and the intermediate frequency signal output by the mixer 1033, and this phase difference reflects the difference between the current output frequency of the YIG tuning oscillator and the target frequency. The present invention adopts a multiplication factor design of N=1, so that the phase detector 1031 works at a lower frequency, reduces the noise contribution of the phase detector itself, and improves the accuracy of phase error detection.

[0040] Furthermore, in the present invention, the YIG tuned oscillator 1032 dynamically adjusts its output frequency according to the error control signal generated by the phase detector 1031 to lock and track the target frequency. Compared with the existing broadband voltage-controlled oscillator (VoltageControlled Oscillator, referred to as VCO), the YIG tuned oscillator 1032 has a higher Q value and lower phase noise, so that the phase noise performance of the entire system is significantly improved.

[0041] In order to make the final RF output ultra-low spurious signals, it is necessary to suppress spurious signals from different sources. Figure 1 As shown, in the wide-band ultra-low phase noise frequency source provided by the present invention, the spurious signals generated by three spurious sources are suppressed, specifically:

[0042] The first spurious source is generated by the continuous spectrum generator 1021 (equally spaced continuous spectrum generator) in the second branch circuit 102. This is because the equally spaced continuous spectrum generator generates a multi-carrier signal (the signal includes multiple equally spaced continuous wave signals). When the phase-locked loop circuit 103 is working, only one of the signals will be input into the mixer 1033 of the phase-locked loop circuit 103 as a local oscillator signal at a time. Other signals are not needed and are regarded as interference signals, which will generate spurious signals and appear in the radio frequency signal. Therefore, the present invention connects an ultra-narrowband electrically tunable bandpass filter 1022 after the continuous spectrum generator 1021 of the second branch circuit 102, so as to filter out all unnecessary signals to improve spurious suppression. In the present invention, the minimum spacing between the output signal of the continuous spectrum generator 1021 and the final RF output signal is 100MHz, and the suppression of the ultra-narrowband electrically tunable bandpass filter 1022 at 100MHz is greater than 85dB, and through the reverse isolation of the mixer 1033 and the amplifier in the phase-locked loop circuit 103, the spurious suppression generated by the redundant carrier signal is greater than 95dBc.

[0043] The second source of spurious signals is the path where the local oscillator signal directly leaks into the RF output signal. The spurious signals generated by this path can be suppressed by the structure of the phase-locked loop circuit 103 provided by the present invention, wherein in the phase-locked loop circuit 103, the selected mixer 1033 has a high RF local oscillator isolation, which can reach 45dB to 50dB; the seventh amplifier 1036 provides reverse isolation, which can provide 35dB isolation; the power divider / coupler 1035 can provide 20dB to 25dB isolation. The isolation generated by the superposition of the above three devices can reach 100dB to 110dB, and the impact on the final output spurious signals is less than 95dBc.

[0044] The third spurious source is the direct digital frequency synthesizer 1011. The various spurious generated can be divided into near-end spurious and far-end spurious, wherein the near-end spurious and far-end spurious can be determined by a preset frequency offset. For this kind of spurious, the present invention adopts a low phase noise and high-resolution direct digital frequency synthesizer, which suppresses spurious by 75dBc. For far-end spurious falling outside the loop, the present invention filters out the loop filter 1034 and the intermediate frequency filter 1037 in the phase-locked loop circuit 103, and the final suppression can reach 95dBc. For near-end spurious falling within the loop bandwidth, the direct digital frequency synthesizer 1011 is compensated by a corresponding algorithm, so that the output spurious of the direct digital frequency synthesizer 1011 is reduced to 95dBc.

[0045] Based on the combination of the three circuit structures in the wide-band ultra-low phase noise frequency source provided by the present invention, the final RF output spurious can reach 95dBc.

[0046] The broadband ultra-low phase noise frequency source provided by the present invention combines a phase-locked loop with a frequency multiplier to achieve the requirements of ultra-low phase noise and broadband, and has higher frequency resolution, so that the generated signal has lower phase noise, high clutter suppression and a wide frequency range.

[0047] On the basis of the above embodiment, the broadband ultra-low phase noise frequency source further includes an ultra-low phase noise reference source, wherein:

[0048] The ultra-low phase noise reference source includes a power divider 104, and the ultra-low phase noise reference source is used to input the generated low phase noise signal into the power divider 104 for branching processing to obtain two paths of the low phase noise reference signal, and input one of the low phase noise reference signals into the first branch circuit 101, and input the other low phase noise reference signal into the second branch circuit 102.

[0049] On the basis of the above embodiment, the output frequency of the ultra-low phase noise reference source is 100 MHz, and the phase noise of the ultra-low phase noise reference source meets the following condition: -180 dBc@10 kHz.

[0050] In the present invention, reference may be made to Figure 1 As shown, the ultra-low phase noise reference source ( Figure 1 An electronic device (not specifically shown) that can generate a signal with very low phase noise. Phase noise is one of the important indicators of signal quality, which describes the change of signal frequency stability over time. Low phase noise means that the signal frequency stability is higher, that is, the fluctuation (or phase jitter) of the signal frequency is very small.

[0051] In the present invention, an ultra-low phase noise reference source is used to generate low phase noise signals, and these signals are input into the power divider 104 for branching processing. The power divider 104 is a device that can divide the power of one input signal into two or more outputs, and the amplitude and phase of each output signal are as consistent as possible. After being processed by the power divider 104, the low phase noise signal is distributed to two branch circuits, namely the first branch circuit 101 and the second branch circuit 102.

[0052] In the present invention, the signal frequency generated by the ultra-low phase noise reference source is 100MHz, and the phase noise meets -180dBc@10kHz, which is the prerequisite for the wide-band ultra-low phase noise frequency source to achieve ultra-low phase noise, and provides a stable and reliable signal source for complex electronic systems.

[0053] Based on the above embodiment, the first branch circuit 101 further includes a first amplifier 1012, a first frequency multiplier 1013, a first bandpass filter 1014, a second amplifier 1015 and a second bandpass filter 1016, wherein:

[0054] The input end of the first amplifier 1012 is connected to the first output end of the power divider 104, the output end of the first amplifier 1012 is connected to the input end of the first frequency multiplier 1013, the output end of the first frequency multiplier 1013 is connected to the input end of the first bandpass filter 1014, the output end of the first bandpass filter 1014 is connected to the input end of the second amplifier 1015, the output end of the second amplifier 1015 is connected to the input end of the direct digital frequency synthesizer 1011, the output end of the direct digital frequency synthesizer 1011 is connected to the input end of the second bandpass filter 1016, and the output end of the second bandpass filter 1016 is connected to the first input end of the phase detector 1031 in the phase-locked loop circuit 103;

[0055] When near-end spurs exist at the target frequency point output by the direct digital frequency synthesizer 1011, the direct digital frequency synthesizer 1011 suppresses the near-end spurs according to the received compensation data to reduce the spurs of the output signal to 95 dBc.

[0056] Based on the above embodiment, the output frequency range of the direct digital frequency synthesizer 1011 is 100 MHz to 200 MHz, and the frequency step is 0.1 mHz.

[0057] In the present invention, the low phase noise reference signal is first divided into two signals by the power divider 104, one of which enters the first branch circuit 101, is amplified by the first amplifier 1012, and then input into the first frequency multiplier 1013, so that the first frequency multiplier 1013 outputs a high-frequency low phase noise frequency signal, and the high-frequency low phase noise frequency signal then passes through the first bandpass filter 1014 and the second amplifier 1015 in sequence to generate a reference signal of the direct digital frequency synthesizer 1011, that is, the first reference signal.

[0058] Further, after receiving the first reference signal, the direct digital frequency synthesizer 1011 outputs a segment of ultra-low phase noise fine-step continuous signal, and inputs the signal to the phase detector 1031 as the reference signal of the phase-locked loop circuit 103, i.e., the second reference signal. In the present invention, some frequency points output by the direct digital frequency synthesizer 1011 will generate near-end spurious signals, and these frequency points will be pre-recorded in the high-speed controller 105. When these frequency points are used (i.e., target frequency points), the high-speed controller 105 will send compensation data to the direct digital frequency synthesizer 1011 according to the relevant compensation algorithm, thereby ensuring that the near-end spurious signals of the output signal are lower than 95dBc.

[0059] The present invention aims at the problem of poor fractional spurious performance of the existing mixer phase-locked loop, and controls the output frequency of the direct digital frequency synthesizer 1011 through a high-speed controller (such as FPGA), wherein the output frequency range of the direct digital frequency synthesizer 1011 used in the present invention is 100 MHz to 200 MHz, and the frequency step is 0.1 mHz. The present invention uses an ultra-low phase noise, low spurious direct digital frequency synthesizer to generate a fine-step fractional reference signal, and its spurious suppression is greater than 95 dBc. Since the multiplication factor N=1 of the overall loop, the spurious performance will not deteriorate, and the final output spurious performance is greater than 95 dBc.

[0060] Based on the above embodiment, the second branch circuit 102 includes a third amplifier 1023, a second frequency multiplier 1024, a third bandpass filter 1025, a fourth amplifier 1026, a fifth amplifier 1027, a sixth amplifier 1028 and an attenuator 1029, wherein:

[0061] The input end of the third amplifier 1023 is connected to the second output end of the power divider 104, the output end of the third amplifier 1023 is connected to the input end of the second frequency multiplier 1024, the output end of the second frequency multiplier 1024 is connected to the input end of the third bandpass filter 1025, the output end of the third bandpass filter 1025 is connected to the input end of the fourth amplifier 1026, the output end of the fourth amplifier 1026 is connected to the input end of the continuous spectrum generator 1021, the output end of the continuous spectrum generator 1021 is connected to the input end of the fifth amplifier 1027, the output end of the fifth amplifier 1027 is connected to the input end of the ultra-narrowband electrically tunable bandpass filter 1022, the output end of the ultra-narrowband electrically tunable bandpass filter 1022 is connected to the input end of the sixth amplifier 1028, the output end of the sixth amplifier 1028 is connected to the input end of the attenuator 1029, and the output end of the attenuator 1029 is connected to the first input end of the mixer 1033 in the phase-locked loop circuit 103.

[0062] In view of the problems that the existing mixing frequency phase-locked loop has poor spurious index and is easy to mislock, and needs to add auxiliary locking circuit, etc. The frequency offset phase-locked loop provided by the present invention adopts a continuous spectrum generator combined with an ultra-narrowband electrically adjustable bandpass filter to avoid mislocking, and simplifies the circuit, which can further improve spurious.

[0063] In the present invention, another identical low phase noise reference signal output from the power divider 104 passes through the third amplifier 1023, the second frequency multiplier 1024, the third bandpass filter 1025 and the fourth amplifier 1026 in sequence, so as to amplify and filter the low phase noise reference signal. Further, the processed low phase noise reference signal enters the equally spaced continuous spectrum generator (i.e., the continuous spectrum generator 1021) to generate an equally spaced continuous spectrum signal. In the present invention, the equally spaced continuous spectrum signal is input to the fifth amplifier 1027 to prevent the signal amplitude from being too small and thus deteriorating the far-end phase noise. Specifically, the continuous spectrum generator is an equally spaced continuous spectrum generator, and when the output frequency interval of the equally spaced continuous spectrum generator is 200MHz and the carrier frequency is 10GHz, the phase noise of the equally spaced continuous spectrum generator meets the following conditions: -138dBc / Hz@10kHz.

[0064] Furthermore, the fifth amplifier 1027 outputs an amplified signal, which passes through an ultra-narrowband electrically tunable bandpass filter 1022, and the ultra-narrowband electrically tunable bandpass filter 1022 outputs a single-point frequency signal corresponding to the target frequency of the final output. In the present invention, the frequency selection of the ultra-narrowband electrically tunable bandpass filter 1022 is calculated by a high-speed controller according to the target frequency. Specifically, the ultra-narrowband electrically tunable bandpass filter satisfies the following conditions: the relative bandwidth of the ultra-narrowband electrically tunable bandpass filter is less than or equal to 0.5%, and the corresponding bandwidth when the signal attenuation reaches 85dB is less than or equal to 100MHz, and the corresponding bandwidth when the signal attenuation reaches 100dB is less than or equal to 200MHz.

[0065] In the present invention, after the ultra-narrowband electrically tunable bandpass filter 1022 outputs a single-point frequency signal, the single-point frequency signal is sequentially input to the mixer 1033 through the sixth amplifier 1028 and the attenuator 1029, thereby serving as a local oscillator driving signal for the mixer 1033. In the present invention, the sixth amplifier 1028 and the attenuator 1029 can improve signal isolation and improve the spurious of the frequency source.

[0066] On the basis of the above embodiment, the phase-locked loop circuit 103 includes a loop filter 1034, a power divider / coupler 1035, a seventh amplifier 1036, an intermediate frequency filter 1037 and an eighth amplifier 1038, wherein:

[0067] The output end of the phase detector 1031 is connected to the input end of the loop filter 1034, the output end of the loop filter 1034 is connected to the input end of the YIG tuning oscillator 1032, the output end of the YIG tuning oscillator 1032 is connected to the input end of the power divider / coupler 1035, the first output end of the power divider / coupler 1035 is connected to the input end of the seventh amplifier 1036, the second output end of the power divider / coupler 1035 outputs a radio frequency signal, the output end of the seventh amplifier 1036 is connected to the second input end of the mixer 1033, the output end of the mixer 1033 is connected to the input end of the intermediate frequency filter 1037, the output end of the intermediate frequency filter 1037 is connected to the input end of the eighth amplifier 1038, and the output end of the eighth amplifier 1038 is connected to the second input end of the phase detector 1031;

[0068] When the direct digital frequency synthesizer 1011 generates far-end spurious signals, the loop filter 1034 and the intermediate frequency filter 1037 filter out the far-end spurious signals to reduce the generated spurious signals to 95 dBc.

[0069] The ultra-narrowband electrically tunable bandpass filter 1022 is further used to filter out interference signals other than the target signal from the multi-carrier signal generated by the continuous spectrum generator 1021, wherein the target signal is the signal in the multi-carrier signal that forms the local oscillator driving signal;

[0070] The mixer 1033 , the seventh amplifier 1036 and the power divider / coupler 1035 form a reverse isolation circuit for suppressing spurious signals generated by the interference signal.

[0071] In the present invention, the mixer 1033 outputs the mixed intermediate frequency signal, which is amplified and filtered by the intermediate frequency filter 1037 and the eighth amplifier 1038 and then input to the phase detector 1031. The phase detector 1031 compares the amplified and filtered intermediate frequency signal with the second reference signal to generate an error control signal, which is then converted into a control voltage after passing through the loop filter 1034.

[0072] Aiming at the problem that the existing broadband VCO device has a low Q value, resulting in poor open-loop phase noise, the present invention adopts a YTO oscillator to replace the existing broadband VCO device, while achieving ultra-low phase noise, further reducing the loop bandwidth and improving the output spurious level.

[0073] In the present invention, the YIG tuned oscillator 1032 outputs a target frequency signal under the control of a control voltage. Specifically, the phase noise of the YIG tuned oscillator satisfies the following conditions: -150dBc / Hz@1MHz or -167dBc / Hz@10MHz. The present invention uses a high-speed controller to set the polarity of the phase detector 1031 according to whether the current output frequency belongs to low offset or high offset, so that the phase-locked loop is always kept in a negative feedback state, thereby locking normally, and realizing a wide-band ultra-low phase noise frequency source with a frequency coverage range of one octave 6 GHz to 12GHz, a frequency step of 0.1mHz, and spurious suppression>95dBc, and at a carrier frequency of 10GHz, the phase noise satisfies the phase noise of -126dBc / Hz@1kHz, -138dBc / Hz@10kHz, -148dBc / Hz@1MHz, and -165dBc / Hz@10MHz.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A broadband ultra-low phase noise frequency source, characterized in that: It includes a first branch circuit, a second branch circuit and a phase-locked loop circuit, wherein: The first branch circuit includes a direct digital frequency synthesizer, which is used to perform frequency multiplication and filtering and amplification processing on the received low phase noise reference signal to obtain a first reference signal, and input the first reference signal into the direct digital frequency synthesizer to obtain a second reference signal; The second branch circuit includes a continuous spectrum generator and an ultra-narrowband electrically tunable bandpass filter, and is used to sequentially input the received low phase noise reference signal to the continuous spectrum generator and the ultra-narrowband electrically tunable bandpass filter to obtain a local oscillator driving signal required by the mixer in the phase-locked loop circuit; The phase-locked loop circuit includes a phase detector, a YIG tuning oscillator and the mixer, wherein the mixer is used to input the generated intermediate frequency signal into the phase detector after receiving the local oscillator driving signal; the phase detector is used to compare the intermediate frequency signal with the second reference signal and generate a corresponding error control signal according to the comparison result; the YIG tuning oscillator is used to generate a target frequency signal according to the error control signal; The phase-locked loop circuit comprises a loop filter, a power divider / coupler, a seventh amplifier, an intermediate frequency filter and an eighth amplifier, wherein: The output end of the phase detector is connected to the input end of the loop filter, the output end of the loop filter is connected to the input end of the YIG tuning oscillator, the output end of the YIG tuning oscillator is connected to the input end of the power divider / coupler, the first output end of the power divider / coupler is connected to the input end of the seventh amplifier, the second output end of the power divider / coupler outputs a radio frequency signal, the output end of the seventh amplifier is connected to the second input end of the mixer, the output end of the mixer is connected to the input end of the intermediate frequency filter, the output end of the intermediate frequency filter is connected to the input end of the eighth amplifier, and the output end of the eighth amplifier is connected to the second input end of the phase detector; Wherein, when the direct digital frequency synthesizer generates far-end spurious, the loop filter and the intermediate frequency filter filter out the far-end spurious to reduce the generated spurious to 95 dBc; The ultra-narrowband electrically tunable bandpass filter is further used to filter out interference signals other than the target signal in the multi-carrier signal generated by the continuous spectrum generator, wherein the target signal is the signal in the multi-carrier signal that forms the local oscillator drive signal; The mixer, the seventh amplifier and the power divider / coupler form a reverse isolation circuit for suppressing spurious signals generated by the interference signal.

2. The broadband ultra-low phase noise frequency source according to claim 1, characterized in that: The broadband ultra-low phase noise frequency source also includes an ultra-low phase noise reference source, wherein: The ultra-low phase noise reference source includes a power divider, and the ultra-low phase noise reference source is used to input the generated low phase noise signal into the power divider for branching processing to obtain two paths of the low phase noise reference signal, and input one of the low phase noise reference signals into the first branch circuit, and input the other low phase noise reference signal into the second branch circuit.

3. The broadband ultra-low phase noise frequency source according to claim 2, characterized in that: The first branch circuit further includes a first amplifier, a first frequency multiplier, a first bandpass filter, a second amplifier and a second bandpass filter, wherein: The input end of the first amplifier is connected to the first output end of the power divider, the output end of the first amplifier is connected to the input end of the first frequency multiplier, the output end of the first frequency multiplier is connected to the input end of the first band-pass filter, the output end of the first band-pass filter is connected to the input end of the second amplifier, the output end of the second amplifier is connected to the input end of the direct digital frequency synthesizer, the output end of the direct digital frequency synthesizer is connected to the input end of the second band-pass filter, and the output end of the second band-pass filter is connected to the first input end of the phase detector in the phase-locked loop circuit; When near-end spurs exist at the target frequency point output by the direct digital frequency synthesizer, the direct digital frequency synthesizer suppresses the near-end spurs according to the received compensation data to reduce the spurs of the output signal to 95 dBc.

4. The broadband ultra-low phase noise frequency source according to claim 2, characterized in that: The second branch circuit includes a third amplifier, a second frequency multiplier, a third bandpass filter, a fourth amplifier, a fifth amplifier, a sixth amplifier and an attenuator, wherein: The input end of the third amplifier is connected to the second output end of the power divider, the output end of the third amplifier is connected to the input end of the second frequency multiplier, the output end of the second frequency multiplier is connected to the input end of the third bandpass filter, the output end of the third bandpass filter is connected to the input end of the fourth amplifier, the output end of the fourth amplifier is connected to the input end of the continuous spectrum generator, the output end of the continuous spectrum generator is connected to the input end of the fifth amplifier, the output end of the fifth amplifier is connected to the input end of the ultra-narrowband electrically tunable bandpass filter, the output end of the ultra-narrowband electrically tunable bandpass filter is connected to the input end of the sixth amplifier, the output end of the sixth amplifier is connected to the input end of the attenuator, and the output end of the attenuator is connected to the first input end of the mixer in the phase-locked loop circuit.

5. The broadband ultra-low phase noise frequency source according to claim 2, characterized in that: The output frequency of the ultra-low phase noise reference source is 100 MHz, and the phase noise of the ultra-low phase noise reference source meets the following conditions: -180 dBc@10 kHz.

6. The broadband ultra-low phase noise frequency source according to claim 1, characterized in that: The phase noise of the YIG tuned oscillator meets the following conditions: -150dBc / Hz@1MHz or -167dBc / Hz@10MHz.

7. The broadband ultra-low phase noise frequency source according to claim 1, characterized in that: The continuous spectrum generator is an equally spaced continuous spectrum generator. When the interval of the output frequency of the equally spaced continuous spectrum generator is 200 MHz and the carrier frequency is 10 GHz, the phase noise of the equally spaced continuous spectrum generator meets the following conditions: -138 dBc / Hz@10 kHz.

8. The broadband ultra-low phase noise frequency source according to claim 1, characterized in that: The ultra-narrowband electrically tunable bandpass filter meets the following conditions: the relative bandwidth of the ultra-narrowband electrically tunable bandpass filter is less than or equal to 0.5%, and the corresponding bandwidth when the signal attenuation reaches 85dB is less than or equal to 100MHz, and the corresponding bandwidth when the signal attenuation reaches 100dB is less than or equal to 200MHz.

9. The broadband ultra-low phase noise frequency source according to claim 1, characterized in that: The output frequency range of the direct digital frequency synthesizer is 100 MHz to 200 MHz, and the frequency step is 0.1 mHz.

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