CN102780490B - DDS (direct digital synthesis) type ultra-wide band frequency-modulated signal generating circuit and method - Google Patents
DDS (direct digital synthesis) type ultra-wide band frequency-modulated signal generating circuit and method Download PDFInfo
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Abstract
The invention belongs to the technical field of radar wideband frequency synthesis and in particular relates to an ultra-wide band frequency-modulated signal generating method which is based on the combination of wideband DDS (direct digital synthesis) and an analog frequency synthesis technique. According to the invention, a wideband DDS chip is used for directly generating a wideband linear frequency-modulated, non-linear frequency-modulated or special phase-coded signal, and waveform signal parameters can be configured online by an upper computer. A radio frequency microwave band datum reference signal is generated by utilizing an analog phase-locked loop and a frequency synthesis technique, and the wideband linear frequency-modulated, non-linear frequency-modulated or special phase-coded signal and the radio frequency microwave band datum reference signal are combined by virtue of frequency spectrum shifting, thus an ultra-wide band frequency-modulated signal with low spur, low phase noise and high resolution is generated, a microwave direct frequency synthesizer with high resolution and low phase noise is realized and is simple in structure and easy to integrate.
Description
Technical field
The invention belongs to radar wideband frequency complex art field, be specifically related to a kind of ultra broadband FM signal production method combining with analog frequency synthetic technology based on broadband DDS.
Background technology
Along with the development of Modern Electronic Countermeasure technology, the target electromagnetic environment of our required reply is day by day complicated, and radar must further improve the ability of multiple target detection, anti-interference, high-resolution, many environment self-adaptions and target identification.One of key technology that improves these performances is exactly to use the long-pending pulsed frequencymodulated signal of wide bandwidth when large, and it is to realize multiobject high-resolution to measure, and completes the essential condition of target classification identification.The generation of this ultra-broadband signal can adopt that direct frequency doubling, up-conversion, DDS combine with frequency multiplication, DDS and the technology such as PLL combines.But the spuious inhibition of direct frequency doubling and up-conversion method is undesirable, the more complicated and debug difficulties of system.General Direct Digital frequency synthesis (DDS) technology that adopts produces arrowband linear FM signal at present, by direct frequency doubling technology or phase locked track frequency doubling technology, carry out bandwidth expansion again and realize ultra broadband FM signal, but frequency multiplier and filter exist larger Amplitude phase distortion, directly affected the quality of output signal.There is longer problem of frequency translation time in phase-locked loop circuit (PLL), cannot produce the ultra broadband FM signal of high-resolution, high linearity.These problems all will greatly limit radar multiobject high-resolution will be measured to ability.
Chinese invention patent < < improves the frequency synthesizer system > > (application number: 200910264176.7) disclosed: a kind of frequency synthesizer system that improves Direct Digital Synthesizer spectral purity of Direct Digital Synthesizer spectral purity.This patent is not enough to some extent in frequency spectrum coverage, has the not high enough true point of output signal frequency.
Summary of the invention
For the deficiency of background technology, the invention provides ultra broadband FM signal generation circuit and method that a kind of DDS directly forms formula.The method directly produces wide-band LFM, nonlinear frequency modulation or special phase-coded signal by broadband DDS chip, and can be by host computer Configuration Online waveform signal parameter.Utilize analog phase-locked look and frequency synthesis technique to produce the accurate reference signal of frequency microwave segment base, again by frequency spectrum shift by the two combination, thereby produce lowly spuiously, low make an uproar mutually, high-resolution ultra broadband FM signal, realized there is high-resolution, low microwave direct synthesizer of making an uproar mutually, and simple in structure be easy to integrated.
Technical scheme of the present invention is: DDS directly forms the ultra broadband FM signal production method of formula, and its feature comprises the steps:
Step 1: external clock input;
Step 2: system clock produces;
Step 3: ultra-wideband waveform produces;
Step 4: waveform parameter is controlled;
Step 5: mixing and filtering.
Its beneficial effect is: produce lowly spuiously, low make an uproar mutually, high-resolution ultra broadband FM signal, realized there is high-resolution, low microwave direct synthesizer of making an uproar mutually.
Ultra broadband FM signal production method as above, is characterized in that the concrete grammar that system clock in described step 2 produces is: by phase locked source and Circuit Matching and power amplifier module, formed and utilized outside input clock to generate broadband waveform generating portion work system clock.
Ultra broadband FM signal production method as above, is characterized in that: the concrete grammar that in described step 3, ultra-wideband waveform produces is: according to the control of parameter controlling section, utilize ultra broadband DDS chip to produce required waveform.Its beneficial effect is: by this step, in the time of can realizing under system clock, can produce the waveform signal that highest frequency is system clock frequency 1/2nd.
Ultra broadband FM signal production method as above, it is characterized in that: the concrete grammar that in described step 4, waveform parameter is controlled is: by ARM controller and PERCOM peripheral communication, utilize the order of the fpga chip parsing host computer that regulates in real time waveform parameter, call corresponding waveform library to waveform generation module output waveform parameter control command.Its beneficial effect is: can produce the waveform that meets particular requirement.
Ultra broadband FM signal production method as above, is characterized in that: in described step 5, the concrete grammar of mixing and filtering is to utilize frequency mixer by above-mentioned produced ultra-wideband waveform and carrier frequency mixing.Its beneficial effect is: this part is realized by frequency mixer, its objective is by the mode of mixing wide-band LFM signal is moved to microwave frequency band, because the output frequency of DDS is lower, in order to make the final wide-band LFM signal producing there is higher microwave working frequency range, need to wide-band LFM signal be moved to microwave frequency band by the mode of mixing, generation initial frequency is
, chirp rate is K, pulsewidth is τ, the pulse repetition period ultra-wideband pulse modulation linearity FM signal that is T.
The ultra broadband FM signal that a kind of DDS directly forms formula produces circuit, comprise clock input circuit, phase locked source circuit, ultra broadband DDS, waveform parameter control circuit, amplification filtering and mixing and filtering circuit, the input of clock input circuit is connected with external clock, output one tunnel of clock input circuit is connected with the reference clock end of phase locked source, and another road enters end with the clock of waveform parameter control circuit and is connected; The system clock output of phase locked source is connected with the system clock input of ultra broadband DDS; The control signal output of waveform parameter control circuit is connected with the control signal input of ultra broadband DDS; The waveform output of ultra broadband DDS is connected with the input of amplification filtering, and the output of amplification filtering is connected with the waveform signal input of mixing.
Its beneficial effect is: produce lowly spuiously, low make an uproar mutually, high-resolution ultra broadband FM signal, realized there is high-resolution, low microwave direct synthesizer of making an uproar mutually.
Ultra broadband FM signal as above produces circuit, it is characterized in that: described phase locked source is comprised of 1/4 frequency divider, phase discriminator PE3336, loop filter, voltage controlled oscillator VCO and amplification merit portions; Wherein the input of 1/4 frequency divider is connected with external clock input circuit, the output of 1/4 frequency divider is connected with phase discriminator PE3336 Yi road reference signal input, another road reference signal input of phase discriminator PE3336 is connected with the feedback signal output that amplification merit is divided, and the output of phase discriminator PE3336 is connected with the input port of loop filter; Loop filter adopts active proportional-integral filter, and output is connected with the control voltage input end of voltage controlled oscillator; The signal output part of voltage controlled oscillator is connected with the input that amplifies merit portions; A wherein road output of amplifying merit parallel circuit is connected with the input end of clock of ultra broadband DDS.
Ultra broadband FM signal as above produces circuit, it is characterized in that: ultra broadband DDS is turned single-ended chip and formed by single-ended transfer difference chip, DDS chip DS855, difference, wherein the input of single-ended transfer difference chip is connected with the system clock output of phase-locked loop, and output is connected with the system clock input of DDS chip DS855; The control signal input of DDS chip DS855 is connected with the control signal input of waveform parameter control module, and the wideband frequency modulation waveform output that DDS chip DS855 produces turns single-ended chip input with difference and is connected; Difference turns single-ended chip output and is connected with the input of amplification filtering.
Accompanying drawing explanation
Fig. 1: working-flow figure
Fig. 2: system architecture diagram
Fig. 3: phase locked source composition frame chart.
Embodiment
The ultra broadband FM signal that a kind of DDS directly forms formula produces circuit and method, it is characterized in that: be the structure composition frame chart of native system as shown in Figure 2, system is mainly partly comprised of clock input, phase locked source, ultra broadband DDS, waveform parameter control, amplification filtering and mixing and filtering.The input of clock input is connected with external clock, and output one tunnel is connected with the reference clock end of phase locked source, and a road enters end with the clock of waveform parameter control circuit and is connected.The system clock output of phase locked source is connected with the system clock input of ultra broadband DDS.The control signal output of waveform parameter control circuit is connected with the control signal input of ultra broadband DDS.The waveform output of ultra broadband DDS is connected with the input of filtering and amplifying circuit, and the input of filtering and amplifying circuit is connected with the waveform signal input of frequency mixing module, and the output of mixing and filtering is connected with output interface.
By the above critical piece, just can realize that according to waveform code, to produce the repetition period be T, carrier frequency is
, pulse duration τ is respectively 100 μ s or 300 μ s or 600 μ s, and bandwidth B is respectively the object of the linear FM signal of 300MHz or 30MHz or 10MHz.And with crossing CAN interface, host computer can be changed the parameter value of repetition period T, pulse duration τ and bandwidth B in waveform library online in real time.
The external clock of system is selected to determine according to the characteristic of phase discriminator in the frequency of required output waveform signals and phase locked source, the external clock 200MHz in the present embodiment.First external clock is divided into two-way after merit is divided, and phase locked source is exported in a road after impedance matching and power amplification, and the object of impedance matching and power amplification is that the clock signal that guarantees input phase locked source has enough power.FPGA for Waveform Control is exported to as its work clock in another road after oversampling clock is processed, and clock processing can be converted to external clock the level format that device can correctly be processed.
The structure of phase locked source as shown in Figure 3, for generation of the radio frequency system clock of high stable
work clock as DDS waveform generation part.VCO is wherein voltage controlled oscillator.It is characterized by: structure is comprised of 1/4 frequency divider, phase discriminator PE3336, loop filter, voltage controlled oscillator and amplification merit portions.Wherein the input of 1/4 frequency divider is connected with the output of external clock input module Yi road as the reference signal input of phase-locked loop module, and output is connected with phase discriminator Yi road reference signal input.Another road reference signal input of phase discriminator is connected with the feedback signal output that amplifies power amplifier module, and output is connected with the input port of loop filter.Loop filter adopts active proportional-integral filter, and output is connected with the control voltage input end of voltage controlled oscillator.The signal output part of voltage controlled oscillator is connected with the input that amplifies merit portions.Amplify merit portions input signal is amplified and is divided into two-way afterwards, a road is connected with phase discriminator as feedback signal, and a road is connected with the input end of clock that ultra-wideband waveform produces DDS as the system clock of the output of phase-locked loop module.First 200MHz clock is 50MHz reference clock signal by 1/4 frequency divider frequency division, this reference clock
enter in the phase discriminator in phase-locked loop chip and participate in phase demodulation, another road phase discrimination signal of phase discriminator is the feedback signal of voltage controlled oscillator VCO output
clock at the inner frequency division specific factor of phase-locked loop chip gained.An error control voltage of phase discriminator output filters high-frequency signal after loop filter, enters the output frequency that VCO regulates VCO, uses active proportional-integral filter as loop filter in native system.The output signal of VCO is amplified into power splitter through power amplifier, uses power amplifier can guarantee that the signal that enters into power splitter has enough power herein, the effect of level isolation before and after can playing again.Amplification filtering is divided into two-way by signal, and a road is as the system clock of DDS
, another road signal
feed back to the feedback loop that lock phase discriminator forms phase locked source inside.
Ultra broadband DDS part is for generation of the waveform signal that meets particular requirement, it is characterized by: structure comprises that single-ended transfer difference circuit, Direct Digital frequency synthesis chip DS855, difference turn single-end circuit, input is wherein connected with the system clock output of phase-locked loop module, and output is connected with the system clock input of DS855.The control signal input of DS855 is connected with the control signal input of waveform parameter control module, and the wideband frequency modulation waveform output of generation is connected with input.Output is connected with the input of filter circuit.Its work clock is the 2.5GHz system clock that above-mentioned phase locked source produces
during work, by Waveform Control FPGA, according to the waveform library data of storage, produce the DDS chip that corresponding Waveform Control word sends to waveform generation part, by the real-time control of Waveform Control part, regulate the output signal parameter of DDS waveform generation part, thus generating center frequency
, the ultra-wideband pulse modulation linearity FM signal that meets the demands of chirp rate K, pulse duration τ.At the DDS chip that native system is selected, support the system clock up to 3.2G, can export 0--1.6GHz frequency agility sine wave signal, and have 32bit frequency control word FTW interface, there is frequency hopping speed fast, the advantage that frequency resolution is high, can be good at meeting design requirement.
Waveform parameter control section is for controlling in real time the parameter that DDS partly produces waveform, FPGA by the ARM for upper machine communication and generation Waveform Control word forms, FPGA part is when work, first receive the Waveform Control order that ARM partly sends, by the pre-stored good waveform library of command lookup, parse the pulsewidth that this orders required generation waveform, bandwidth, repetition period special parameter, according to the initial frequency of these calculation of parameter sequential relationship data and FM signal, step frequency, cut-off frequency, finally produce frequency control word and the timing control signal of specific time sequence relation, for example in the design, producing pulsewidth τ is 100 μ s, repetition period 2ms, the FM signal of bandwidth 300 MHz, and known centre frequency
be fixed as 750MHz, by waveform and time-sequence control module, calculating last generation take system synchronization signal and has the control signal frequency control word of specific time sequence as benchmark, corresponding initial frequency point is 600 MHz, frequency step is 7.5kHz, 40000 Frequency points of this step change of continuous wave output in whole 100 μ s pulsewidths, thus the linear FM signal that 100 μ s pulse duration frequencies are 600 ~ 900MHz produced.And ARM part completes the communication function between waveform generation module and host computer by CAN interface, the output signal of DDS is carried out to On-line Control.CAN debugging software by host computer during work sends CAN order to waveform and time-sequence control module, the order of waveform code is controlled the pulse duration τ corresponding with this waveform code in its generation waveform library and is respectively 100 μ s or 300 μ s or 600 μ s, and bandwidth B is respectively the linear FM signal of 300MHz or 30MHz or 10MHz.The parameter value of the pulse duration of waveform library reorganization order in can the preset waveform library of online modification, bandwidth, centre frequency, realizes the on-line reorganization of waveform library, to be adapted to multiple different environment for use.
Amplification filtering partly adopts the mode of high pass filter and low pass filter combination, for the spurious frequency of filtered signal and the harmonic frequency of phase locked source generation, improves signal quality.
Mixing and filtering part, by linear FM signal up-conversion to microwave frequency band, centre frequency by
move to
, then through the filter with signal waveform the form matches, suppress parasitic frequency, finally export the microwave section wide-band LFM signal of designing requirement.
This technology adopts the method that broadband DDS combines with analog frequency synthetic technology to produce ultra broadband FM signal.Utilize broadband DDS technique of real-time control to realize waveform generation mode and overcome the index defects such as the Hopping time existing in the spread spectrum of traditional arrowband DDS+PLL or arrowband DDS+ frequency multiplication is long, frequency resolution is low, phase resolution is low, combine with analog frequency synthetic technology simultaneously, overcome again the not high enough weakness of output signal frequency in DDS technology, made the FM signal of output can cover L, S, C, X and K wave band.Make to there is high-resolution, the microwave frequency band ultra broadband direct synthesizer of high phase noise index becomes possibility, and simple in structure be easy to integrated.Patent of the present invention is mainly used in high-resolution digital array radar, is one of key technology of target identification, has very high engineering practical value.
When the external clock in the present embodiment is 200MHz, can make certain improvements to the circuit of the present embodiment, realize external clock and change, and then realize the object that will reach the present invention.
Claims (3)
1. DDS directly forms the ultra broadband FM signal production method of formula, and its feature comprises the steps:
Step 1: external clock input;
Step 2: system clock produces; Concrete grammar is: by phase locked source and Circuit Matching and power amplifier module, formed and utilized outside input clock to generate broadband waveform generating portion work system clock;
Step 3: ultra-wideband waveform produces; Concrete grammar is: according to the control of parameter controlling section, utilize ultra broadband DDS chip to produce required waveform;
Step 4: waveform parameter is controlled; Concrete grammar is: by ARM controller and PERCOM peripheral communication, utilize the order of the FPGA chip parsing host computer that regulates in real time waveform parameter, call corresponding waveform library to waveform generation module output waveform parameter control command;
Step 5: mixing and filtering; Concrete grammar is: utilize frequency mixer by above-mentioned produced ultra-wideband waveform and carrier frequency mixing.
2. the ultra broadband FM signal that a DDS directly forms formula produces circuit, comprise clock input circuit, phase locked source circuit, ultra broadband DDS, waveform parameter control circuit, amplification filtering and mixing and filtering circuit, the input of clock input circuit is connected with external clock, output one tunnel of clock input circuit is connected with the reference clock end of phase locked source, and another road enters end with the clock of waveform parameter control circuit and is connected; The system clock output of phase locked source is connected with the system clock input of ultra broadband DDS; The control signal output of waveform parameter control circuit is connected with the control signal input of ultra broadband DDS; The waveform output of ultra broadband DDS is connected with the input of amplification filtering, and the output of amplification filtering is connected with the waveform signal input of mixing; It is characterized in that: ultra broadband DDS is turned single-ended chip and formed by single-ended transfer difference chip, DDS chip DS855, difference, wherein the input of single-ended transfer difference chip is connected with the system clock output of phase-locked loop, and output is connected with the system clock input of DDS chip DS855; The control signal input of DDS chip DS855 is connected with the control signal input of waveform parameter control module, and the wideband frequency modulation waveform output that DDS chip DS855 produces turns single-ended chip input with difference and is connected; Difference turns single-ended chip output and is connected with the input of amplification filtering.
3. the ultra broadband FM signal as described in claim 2 produces circuit, it is characterized in that: described phase locked source is comprised of 1/4 frequency divider, phase discriminator PE3336, loop filter, voltage controlled oscillator VCO and amplification merit portions; Wherein the input of 1/4 frequency divider is connected with external clock input circuit, the output of 1/4 frequency divider is connected with phase discriminator PE3336 Yi road reference signal input, another road reference signal input of phase discriminator PE3336 is connected with the feedback signal output that amplification merit is divided, and the output of phase discriminator PE3336 is connected with the input port of loop filter; Loop filter adopts active proportional-integral filter, and output is connected with the control voltage input end of voltage controlled oscillator; The signal output part of voltage controlled oscillator is connected with the input that amplifies merit portions; A wherein road output of amplifying merit parallel circuit is connected with the input end of clock of ultra broadband DDS.
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| CN103630881B (en) * | 2013-10-28 | 2015-11-18 | 武汉滨湖电子有限责任公司 | A kind of distributed waveform generation on-line synchronous Circuit tuning and method |
| CN104467836B (en) * | 2014-11-10 | 2017-12-08 | 绵阳市维博电子有限责任公司 | A kind of clock signal generating method and system |
| CN104393871A (en) * | 2014-12-02 | 2015-03-04 | 贵州航天计量测试技术研究所 | Frequency synthesizer for driving phase-locked loop after up-converting DDS |
| CN105450256A (en) * | 2015-11-16 | 2016-03-30 | 中国电子科技集团公司第十研究所 | Broadband frequency hopping digital signal generation system |
| CN105553475B (en) * | 2015-12-18 | 2018-11-20 | 中国电子科技集团公司第四十一研究所 | High frequency points frequency source combiner circuit based on digital frequency division and harmonic mixing |
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| CN106788557A (en) * | 2016-11-14 | 2017-05-31 | 成都合立微波技术有限公司 | A kind of digital filtering FM source |
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| CN112087230A (en) * | 2020-09-17 | 2020-12-15 | 中国科学院空天信息创新研究院 | Broadband linear frequency modulation signal generating device and method |
| CN113504513B (en) * | 2021-06-30 | 2023-05-23 | 电子科技大学 | Time domain nonlinear frequency modulation signal generation method |
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