CN104730338A - Spectrum analyzer with frequency mixers at multiple levels - Google Patents
Spectrum analyzer with frequency mixers at multiple levels Download PDFInfo
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- CN104730338A CN104730338A CN201310700463.4A CN201310700463A CN104730338A CN 104730338 A CN104730338 A CN 104730338A CN 201310700463 A CN201310700463 A CN 201310700463A CN 104730338 A CN104730338 A CN 104730338A
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Abstract
The invention provides a spectrum analyzer with frequency mixers at multiple levels, and relates to the field of spectrum analyzing devices. The spectrum analyzer comprises the frequency mixers at the multiple levels and sequentially connected in series, an intermediate-frequency filter is connected behind the frequency mixer at each level in series, and an inductive load is arranged between the frequency mixer at the last level and the intermediate-frequency filter corresponding to the frequency mixer at the last level. On the basis of ensuring that the frequency mixers output an intermediate-frequency signal low in frequency, the inductive load improves non-linear distortion of the frequency mixers, the amplitude of spurious signals of the spectrum analyzer is greatly reduced, the distortion performance of the spectrum analyzer is improved, and the testing frequency spectrum purity of the spectrum analyzer is optimized.
Description
Technical field
The present invention relates to arrangements for analyzing frequency field, particularly a kind of spectrum analyzer with multistage frequency mixer.
Background technology
Spectrum analyzer is a kind of receiver being used for carrying out measured signal spectrum analysis, can measure the correlation parameters such as the frequency of unknown signaling, amplitude, distortion, usually have very wide frequency and amplitude measurement scope.Be mainly used in the fields such as base station maintenance, electronic product research and development, production.Spectrum analyzer can be described as again frequency domain oscillograph, follows the tracks of oscillograph, analyzes oscillograph, harmonic analyzer, frequency characteristic analyzer or Fourier analyzer etc.Modern spectrum analyzer can in an analog fashion or digital form display analysis result, and the very low frequency (VLF) analyzing less than 1 hertz is to the electric signal of whole radio frequency bands of submillimeter region.The key technical indexes of spectrum analyzer has frequency range, resolving power, sweep velocity, sensitivity, display mode and spurious response etc., and spectrum analyzer is generally divided into sweep-frequency Békésy audiometer and real-time analysis formula two class.
With reference to Fig. 1, a kind of spectrum analyzer 100 of prior art adopts the scheme of three grades of mixing, radio-frequency input signals fRF inputs the first frequency mixer 101, the the first local oscillation signal fLO1 mixing exported with the first local oscillator unit 102, first frequency mixer 101 output packet is containing the signal of ± each frequency content of m × fRF ± n × fLO1, this signal inputs to the first intermediate-frequency filter 103, filtering other each frequencies except useful frequency answered in theory by first intermediate-frequency filter 103, export useful frequency f LO1 ?the signal of fRF, the radio frequency as the second frequency mixer 104 inputs.First local oscillation signal fLO1 is swept-frequency signal, object makes the radio-frequency input signals fRF in broadband through the first frequency mixer 101 and the first local oscillation signal fLO1 mixing, by making the first local oscillation signal fLO1 variable, the absolute value of fLO1 ?fRF is made to be a fixing frequency signal.
FLO1 ?the absolute value frequency of fRF be designated as fIF1, input to the second frequency mixer 104, the the second local oscillation signal fLO2 mixing exported with the second local oscillator unit 105, second frequency mixer 104 output packet is containing the signal of ± each frequency content of m × fIF1 ± n × fLO2, this signal inputs to the second intermediate-frequency filter 106, filtering other each frequencies except useful frequency answered in theory by second intermediate-frequency filter 106, and export the signal of useful frequency f IF1 ?fLO2, the radio frequency as three-mixer 107 inputs.FIF1 ?the absolute value of fLO2 be the signal of a fixed frequency.
FIF1 ?the absolute value frequency of fLO2 be designated as fIF2, input to three-mixer 107, the 3rd local oscillation signal fLO3 mixing exported with the 3rd local oscillator unit 108, three-mixer 107 output packet is containing the signal of ± each frequency content of m × fIF2 ± n × fLO3, three-mixer 107 export useful frequency content be fIF2 ?fLO3, other frequency contents in theory all should by filtering.The signal that three-mixer 107 exports is after the 3rd intermediate-frequency filter 109 filtering, produce the 3rd intermediate-freuqncy signal fIF3, the 3rd intermediate-freuqncy signal fIF3 carry out amplifying by input Digital IF Processing module 110 again, ADC sampling send into display module 111 carry out exporting and showing after the process such as digital IF filter, wave detector and video filtering.
Radio-frequency input signals fRF changes through 3 frequency conversions by the spectrum analyzer 100 of prior art, obtain the manageable intermediate-freuqncy signal fIF3 of data intermediate frequency module 110, and after data intermediate frequency module 110 processes, the information such as the frequency of radio-frequency input signals fRF and amplitude can be shown on the screen of spectrum analyzer 100.But actual conditions are, the screen of prior art spectrum analyzer 100 not only show the information such as the frequency of radio-frequency input signals fRF and amplitude, go back display distortion spurious signal simultaneously, cause measurement result inaccurate, the test purity of frequency spectrum is not high.
Summary of the invention
With reference to Fig. 1, in conjunction with reference Fig. 2, in the spectrum analyzer 100 of prior art, filtering other each frequencies except useful frequency answered in theory by the first intermediate-frequency filter 103, export useful frequency f LO1 ?the signal of fRF, the radio frequency as the second frequency mixer 104 inputs; Filtering other each frequencies except useful frequency answered in theory by second intermediate-frequency filter 106, and export the signal of useful frequency f IF1 ?fLO2, the radio frequency as three-mixer 107 inputs; Filtering other each frequencies except useful frequency answered in theory by 3rd intermediate-frequency filter 109, and export the signal of useful frequency f IF2 ?fLO3, the radio frequency as three-mixer 107 inputs; Also just say the 3rd intermediate-freuqncy signal fIF3 should equal in theory fIF2 ?fLO3.Here the 3rd intermediate-freuqncy signal fIF3 is exemplified as a value 10.7M determined by us, fIF2 is 465.7M, fLO3 is 455M, suppose that radio-frequency input signals fRF is input as the signal of 1GHz, first vibration frequency frequency sweep within the scope of f1 ~ f2, when first vibration frequency frequency sweep is to (F=1GHz+fIF1 during F, within the scope of f1 ~ f2), fIF1 can be obtained through the first frequency mixer 101 mixing, the second frequency mixer 104 again on passage, three-mixer 107, the 3rd intermediate-freuqncy signal fIF3 can be obtained, i.e. 10.7M signal, after the process of Digital IF Processing module 110, the display screen of display module 111 can show signal spectrum Figure 20 1 of 1GHz.
Visible, when have 10.7M signal input to Digital IF Processing module 110 process time, on the display screen of display module 111, the correspondence position of radio-frequency input signals will show signal spectrum Figure 20 1.But find in practice, when radio-frequency input signals fRF inputs the signal of 1GHz, first vibration frequency frequency sweep within the scope of f1 ~ f2, when first vibration frequency frequency sweep is to (F ﹣ 5.35M), first frequency mixer 101 output frequency is (fIF1 ﹣ 5.35M), can not by filtering in the cake resistancet that it may drop on the first intermediate-frequency filter 103, after the second frequency mixer 104, this signal frequency conversion is to (fIF2 ﹣ 5.35M), can not by filtering in the cake resistancet that also may drop on the second intermediate-frequency filter 106, this signal is after three-mixer 107, ± m × (fIF2 ﹣ 5.35M) ± n × fLO3 can be comprised in the output of three-mixer 107, as m=n=2, i.e. 2 × (465.7M ﹣ 5.35M) ﹣ 2 × 455M=10.7M, this 10.7M signal can go out have in screen display signal spectrum Figure 20 2 of a 994.65M after Digital IF Processing processing module 110 processes, this signal spectrum Figure 20 2 is actual is the spurious signal with input 1GHz signal correction, this signal spectrum Figure 20 2 is because the non-linear distortion products mixing of three-mixer obtains, the spuious of spectrum analyzer, that user does not wish to see.
Find in practice, if the 3rd intermediate-freuqncy signal fIF3 is not the signal getting a 10.7M, but get the intermediate-freuqncy signal of a hundreds of more than million, so can correspondingly tail off to the spurious signal of input 1GHz signal correction on the display screen of display module 111, but the intermediate-freuqncy signal of hundreds of more than million proposes very high requirement to Digital IF Processing module 110 again, the sampling of Digital IF Processing module 110 inside and ADC intractability are strengthened, high to device performance requirements.
The object of the invention is to: solve prior art spectrum analyzer and there is distortion spurious signal, and the technical matters that the intermediate-freuqncy signal inputting Digital IF Processing module can not be too high, a kind of spectrum analyzer with multistage frequency mixer is provided.
A kind of spectrum analyzer with multistage frequency mixer provided by the invention, comprise the multistage frequency mixer of connecting successively, all to connect after every grade of frequency mixer an intermediate-frequency filter, between the intermediate-frequency filter of in the end one-level frequency mixer and the described afterbody frequency mixer of correspondence, an inductive load is set.
Inductive load of the present invention is ensureing that frequency mixer exports on the basis of a lower intermediate-freuqncy signal, improve the nonlinear distortion of frequency mixer, greatly reduce the amplitude of spectrum analyzer spurious signal, improve the distortion performance of spectrum analyzer, optimize the test purity of frequency spectrum of spectrum analyzer.
As one citing, described inductive load can be an inductance, on the line between the intermediate-frequency filter that one end of described inductance is connected to described afterbody frequency mixer and the described afterbody frequency mixer of correspondence, and the other end ground connection of described inductance.
The design comparison of an inductance is succinct, and can reach the nonlinear distortion improving frequency mixer, reduces the object of the amplitude of spectrum analyzer spurious signal.
Illustrate as one, described inductive load can be a π type Hi-pass filter, described π type Hi-pass filter is serially connected between the intermediate-frequency filter of described afterbody frequency mixer and the described afterbody frequency mixer of correspondence, and the cutoff frequency of described π type Hi-pass filter is less than the IF-FRE of described afterbody frequency mixer output.
Inductive load selects π type Hi-pass filter, and the cutoff frequency of π type Hi-pass filter is less than the IF-FRE that described afterbody frequency mixer exports, to reduce π type three rank Hi-pass filter most possibly to the decay of the useful intermediate-freuqncy signal amplitude of afterbody, and reach with the object of afterbody mixer matches while, less Insertion Loss is had to the useful intermediate-freuqncy signal of afterbody, and the amplifier gain of Digital IF Processing inside modules is not affected, reduce the requirement to rear class design.
As one citing, described π type Hi-pass filter can be three rank Hi-pass filters.
π type Hi-pass filter selects three rank Hi-pass filters, and design is the simplest, and effect is best.
Accompanying drawing explanation
Fig. 1 is the structural representation of prior art spectrum analyzer 100;
Fig. 2 is the output signal spectrogram of prior art spectrum analyzer 100;
Fig. 3 is the structural representation of the spectrum analyzer 300 of the preferred embodiment of the present invention;
Fig. 4 is the output signal spectrogram of preferred embodiment of the present invention spectrum analyzer 300.
Embodiment
Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are further described in detail.
With reference to Fig. 3, the spectrum analyzer 300 of this preferred embodiment comprises the first frequency mixer 301, first intermediate-frequency filter 303, second frequency mixer 304, second intermediate-frequency filter 306, the three-mixer 307 of connecting successively, and be respectively the first frequency mixer 301, second frequency mixer 304, the first local oscillator unit 302, second local oscillator unit 305 and the 3rd local oscillator unit 308 that three-mixer 307 provides the first local oscillation signal fLO1 ', the second local oscillation signal fLO2 ', the 3rd local oscillation signal fLO3 '; Also to connect successively below inductive load unit 312, the 3rd intermediate-frequency filter 309, Digital IF Processing module 310, a display module 311 at three-mixer 307.
In the preferred embodiment, inductive load unit 312 adopts π type three rank Hi-pass filter; Three-mixer 307 select mini company ADE ?12.
As other citing, in originally illustrating, inductive load unit 312 only can adopt an inductance, and one end of described inductance is connected on the line between three-mixer 307 and the 3rd intermediate-frequency filter 309, the other end ground connection of described inductance.
In the preferred embodiment, radio-frequency input signals fRF ' inputs the first frequency mixer 301, the the first local oscillation signal fLO1 ' mixing exported with the first local oscillator unit 302, first frequency mixer 301 output packet is containing the signal of ± each frequency content of m × fRF ' ± n × fLO1 ', this signal inputs to the first intermediate-frequency filter 303, the output signal of the first intermediate-frequency filter 303 to the first frequency mixer 301 carries out filtering, export the first intermediate-freuqncy signal fIF1 ', first intermediate-freuqncy signal fIF1 ' inputs to the second frequency mixer 304, the the second local oscillation signal fLO2 ' mixing exported with the second local oscillator unit 305, second frequency mixer 304 output packet is containing the signal of ± each frequency content of m × fIF1 ' ± n × fLO2 ', this signal inputs to the second intermediate-frequency filter 306, the output signal of the second intermediate-frequency filter 306 to the second frequency mixer 304 carries out filtering, export the second intermediate-freuqncy signal fIF2 ', second intermediate-freuqncy signal fIF2 ' inputs to three-mixer 307, the 3rd local oscillation signal fLO3 ' mixing exported with the 3rd local oscillator unit 308, three-mixer 307 output packet is containing the signal of ± each frequency content of m × fIF2 ' ± n × fLO3 ', three-mixer 307 export signal first after the Hi-pass filter of π type three rank again through the 3rd intermediate-frequency filter 309 filtering, produce the 3rd intermediate-freuqncy signal fIF3 ', 3rd intermediate-freuqncy signal fIF3 ' amplifies by input Digital IF Processing module 310 again, ADC samples, and through digital IF filter, send into display module 311 after the process such as wave detector and video filtering to carry out exporting and showing.
In the preferred embodiment, described π type three rank Hi-pass filter is in the layout of pcb board, and the output terminal as far as possible near three-mixer 307 is arranged.Such layout, considerably reduces the negative effect of parasitic parameter to matching effect of pcb board.
In the preferred embodiment, radio-frequency input signals fRF ' selects 1GHz, the value of the 3rd intermediate-freuqncy signal fIF3 ' is still 10.7M, the cutoff frequency of π type three rank Hi-pass filter elects 9M as, the cutoff frequency of π type three rank Hi-pass filter elects 9M as, while reaching the object of mating with three-mixer 307, to reduce π type three rank Hi-pass filter most possibly to the decay of 10.7M signal amplitude, less frequency response fluctuation is had in the frequency range of 10.7M ± spectrum analyzer 300 maximum RBW bandwidth, and the amplifier gain of Digital IF Processing module 310 inside is not affected, reduce the requirement to rear class design.
See Fig. 4, show the output signal spectrogram of preferred embodiment of the present invention spectrum analyzer 300, the display screen of display module 111 mainly shows signal spectrum Figure 40 1 of 1GHz, and the amplitude of signal spectrum Figure 40 2 of 994.65M significantly reduces, the impact of the signal spectrum Figure 40 1 on 1GHz can be ignored.
As other citing, in originally illustrating, inductive load unit 312 also can adopt the Hi-pass filter on π type 4 rank, 5 rank, even more high-order.
As other citing, in originally illustrating, the cutoff frequency of described π type Hi-pass filter is less than the IF signal frequency of third level frequency mixer 307 output.
As other citing, in originally illustrating, spectrum analyzer 300 is structures of 4 grades of mixing, after inductive load unit 312 is connected on the 4th frequency mixer.
As other citing, in originally illustrating, spectrum analyzer 300 comprises a hf channel, a low channel, hf channel has two-stage mixing, low channel has two-stage mixing, common through afterbody mixing again after the signal exported after the signal exported after the mixing of hf channel two-stage and the mixing of low channel two-stage converges, after described inductive load unit 312 is connected on afterbody frequency mixer.
Inductive load of the present invention is ensureing that frequency mixer exports on the basis of the lower intermediate-freuqncy signal of frequency, improve the nonlinear distortion of frequency mixer, greatly reduce the amplitude of spectrum analyzer spurious signal, improve the distortion performance of spectrum analyzer, optimize the test purity of frequency spectrum of spectrum analyzer.
Above-describedly be only the preferred embodiments of the present invention; be understood that; the explanation of above preferred embodiment just understands method of the present invention and core concept thereof for helping; the protection domain be not intended to limit the present invention; all any amendments, equivalent replacement etc. made within thought of the present invention and principle, all should be included within protection scope of the present invention.
Claims (4)
1. one kind has the spectrum analyzer of multistage frequency mixer, comprise the multistage frequency mixer of connecting successively, all to connect after every grade of frequency mixer an intermediate-frequency filter, it is characterized in that, between the intermediate-frequency filter of in the end one-level frequency mixer and the described afterbody frequency mixer of correspondence, an inductive load is set.
2. spectrum analyzer according to claim 1, it is characterized in that, described inductive load is an inductance, on the line between the intermediate-frequency filter that one end of described inductance is connected to described afterbody frequency mixer and the described afterbody frequency mixer of correspondence, and the other end ground connection of described inductance.
3. spectrum analyzer according to claim 1, it is characterized in that, described inductive load is a π type Hi-pass filter, described π type Hi-pass filter is serially connected between the intermediate-frequency filter of described afterbody frequency mixer and the described afterbody frequency mixer of correspondence, and the cutoff frequency of described π type Hi-pass filter is less than the IF-FRE of described afterbody frequency mixer output.
4. spectrum analyzer according to claim 3, is characterized in that, described π type Hi-pass filter is three rank Hi-pass filters.
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| CN201310700463.4A CN104730338A (en) | 2013-12-19 | 2013-12-19 | Spectrum analyzer with frequency mixers at multiple levels |
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| CN106896269A (en) * | 2015-12-18 | 2017-06-27 | 苏州普源精电科技有限公司 | A kind of spectrum analyzer for improving sensitivity |
| CN105699724B (en) * | 2016-03-25 | 2018-08-14 | 北华航天工业学院 | Long-range hybrid domain analog measurement instrument |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106896269A (en) * | 2015-12-18 | 2017-06-27 | 苏州普源精电科技有限公司 | A kind of spectrum analyzer for improving sensitivity |
| CN105699724B (en) * | 2016-03-25 | 2018-08-14 | 北华航天工业学院 | Long-range hybrid domain analog measurement instrument |
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