阅读说明：本技术 一种频谱扫描测量装置及时域波形获取方法 (Spectrum scanning measuring device and time domain waveform obtaining method ) 是由 高博 童玲 宫珣 王培丞 董雪建 于 2019-10-29 设计创作，主要内容包括：本发明公开了一种频谱扫描测量装置及时域波形获取方法,利用相位可重复信号源作为扫频本振,通过软件控制该本振进行扫描时间间隔已知的频率粗扫描；然后对粗扫描所得中频信号进行快速傅里叶变换,实现频谱细分；接下来分别对信号测量值的幅度和相位进行恢复和校准,幅度的恢复可以在直接利用标准信号来进行标定并通过标定值来进行校准；相位的恢复则需要首先恢复扫频架构非实时测量造成的相位偏移,其次需要消除LO的相位影响,最后利用梳状波发射器和多重正弦波对整个系统的相位进行校准；在频域完成信号幅度和相位的恢复后,将所有的谱分量进行矢量叠加即可获取被测信号的时域波形。(The invention discloses a frequency spectrum scanning measuring device and a time domain waveform acquisition method.A phase repeatable signal source is used as a sweep frequency local oscillator, and the local oscillator is controlled by software to carry out frequency coarse scanning with known scanning time interval; then, performing fast Fourier transform on the intermediate frequency signal obtained by the coarse scanning to realize frequency spectrum subdivision; then respectively restoring and calibrating the amplitude and the phase of the signal measurement value, wherein the restoration of the amplitude can be directly calibrated by using a standard signal and calibrated by a calibration value; the phase recovery firstly needs to recover the phase offset caused by non-real-time measurement of a frequency sweeping framework, secondly needs to eliminate the phase influence of an LO (local oscillator), and finally utilizes a comb wave transmitter and multiple sine waves to calibrate the phase of the whole system; after the frequency domain finishes the recovery of the signal amplitude and the phase, vector superposition is carried out on all the spectral components, and then the time domain waveform of the detected signal can be obtained.)

1. A spectral scanning measurement apparatus, comprising: the system comprises a low-pass filter, a synchronous control module, a frequency conversion link, an analog-to-digital converter and a digital signal processing module;

the low-pass filter is used for filtering an input high-frequency interference signal and preventing the high-frequency interference signal from entering the device in a mirror image mode to interfere the measurement of an effective input signal;

the synchronous control module is used for controlling the frequency conversion link, the analog-to-digital converter and the digital signal processing module to synchronously coordinate according to the triggering of the same clock;

the frequency conversion link comprises n +1 frequency mixers, n +1 band-pass filters, n fixed local oscillators and a phase repeatable swept local oscillator;

wherein, the 0 th order local oscillator is the repeatable frequency sweep local oscillator of phase place, and input signal and the 0 th order local oscillator signal all send into 0 th mixer, will produce following signal under this mixer's effect:

f_IF＝f_LO-f_RF

f_IM＝f_LO+f_RF

then, the 0 th-order band-pass filter will filter out the signal f_IMLeaving only the signal f_IF(ii) a Signal f according to the sampling frequency range of the ADC_IFThe last n mixers, the last n bandpass filters and the n fixed local oscillators form a multi-stage down-conversion link for frequency conversion processing, and the frequency of the intermediate frequency signal is reduced for many times in a cascading mode until the input requirement of the analog-to-digital converter is met;

the analog-to-digital converter performs analog-to-digital conversion on the input analog signal to convert the analog signal into a digital signal, and inputs the digital signal into the digital signal processing module;

the digital signal processing module carries out fast Fourier transform, phase recovery and amplitude and phase calibration on the input digital signal in sequence, so that the time domain waveform of the input signal is reconstructed.

2. A method for acquiring a signal time domain waveform by a spectrum scanning measuring device is characterized by comprising the following steps:

(1) filtering the input high-frequency interference signal by using a low-pass filter, and preventing the high-frequency interference signal from entering a system in a mirror image mode to interfere the measurement of an effective input signal;

(2) the synchronous control module controls the frequency conversion link, the analog-to-digital converter and the digital signal processing module to trigger according to the same clock, so that the device is ensured to carry out frequency scanning measurement according to known and controllable time intervals;

(3) setting the scanning time interval of the phase repeatable sweep frequency local oscillator as T and the frequency spectrum scanning stepping interval as f₀；

(4) Carrying out frequency conversion processing on the frequency of the input signal for multiple times through the frequency conversion link, so that the frequency of the signal output by the frequency conversion link meets the input requirement of the analog-to-digital converter;

(5) the analog-to-digital converter performs analog-to-digital conversion on the input analog signal to convert the analog signal into a digital signal, and inputs the digital signal into the digital signal processing module;

(6) the digital signal processing module carries out Fast Fourier Transform (FFT) on the input digital signal, and distributes the calculated frequency values on a series of discrete sequences with intervals of delta f, wherein the delta f satisfies the following conditions:

wherein f is_sTaking the sampling rate of the ADC and M as the number of points of FFT conversion;

(7) and performing phase recovery on the phase of each frequency component after FFT

(7.1) compensating the delay time of the phase repeatable swept local oscillator

Setting the input signal to be tested and the nth phase repeatable sweep local oscillator signal nf₀In the frequency spectrum of the intermediate frequency signal obtained by mixing, the actual amplitude, phase and frequency values of the corresponding measured input signal at the m delta f frequency are respectively A_nm、And f_nmThen, the frequency value of the input signal to be measured is represented by the phase repeatable swept local oscillator signal and the intermediate frequency signal as:

f_nm＝nf₀-mΔf

then, the measured input signal is actually represented as:

measuring the phase value of the measured input signal due to the effect of the time delay

therefore, the phase change caused by the lag time of the phase repeatable swept local oscillator should be compensated for, the actual phase of the input signal at this frequency being:

(7.2) compensating the local oscillator signal phase

N sweep local oscillator signal nf with phase capable of repeatedly sweeping local oscillator₀Has a phase of

(7.3) calculating the actual value of the phase of each frequency component after phase recovery;

(8) amplitude and phase calibration

(8.1) coarse calibration of amplitude and phase

(8.1.1) useThe comb wave generator generates comb waves with known amplitude and phase of each frequency component, the comb waves are obtained by superposing multiple sine wave signals with sparse frequency intervals in a frequency domain view, and the frequency range of the signals can cover the whole measurement range of the device; let the spectral interval of the sparse multiple sine wave signal be f₁N th₁The amplitude and phase of the subharmonic are respectively

(8.1.2) inputting the sparse multiple sine wave signal as a standard signal into the device for measurement, performing phase recovery on the phase calculation result according to the method in the step (7), and setting the n-th recovered signal₁The amplitude and phase of the subharmonic are respectively

(8.1.3) comparing the recovered amplitude and phase with the known amplitude and phase of the input standard signal to obtain that the device is within the overall measurement range, n₁f₁The coarse calibration values for amplitude and phase at frequency are:

(8.2) Fine calibration of amplitude and phase

(8.2.1) generating a dense multiple sine wave signal having known amplitude and phase of each frequency component, the frequency range of which can be overlapped, by using an arbitrary wave generatorCovering a spectrum interval range of the sparse multiple sine wave signals; setting the frequency starting point of the dense multiple sine wave signal generated in the 1 st coarse calibration frequency interval range as 1f₁Spectral interval of f₂N th₂The amplitude and phase of the subharmonic are respectively

(8.2.2) inputting the dense multiple sine wave signal as a standard signal into the device for measurement, performing phase recovery on the phase calculation result according to the method in the step (7), and setting the n-th recovered signal₂The amplitude and phase of the subharmonic are respectively

(8.2.3) comparing the recovered amplitude and phase with the known amplitude and phase of the input reference signal to obtain the device within a coarse calibration spectral interval, n₂f₂The fine calibration values for amplitude and phase at frequency are:

(8.3) interpolating the coarse calibration value in the entire measurement range of the system device by using the fine calibration value, and then, in the entire measurement range of the device, n₁f₁-n₂f₂The calibration values for amplitude and phase at frequency are:

then, after calibration, the actual values of the amplitude and phase of each frequency component are reconstructed as:

wherein:

nf₀-mΔf＝n₁f₁-n₂f₂

(9) and adding the reconstructed frequency components to reconstruct the time domain waveform of the input measured signal.

Technical Field

The invention belongs to the technical field of electronic measuring instruments, and particularly relates to a frequency spectrum scanning measuring device and a time domain waveform acquiring method.

Background

As known from fourier transformation, a signal can be represented in either the time domain or the frequency domain. Both the frequency domain and the time domain are of great significance for analyzing signals. For electrical signals, oscilloscopes and spectrum analyzers are two typical instruments that analyze the time and frequency domains of a signal, respectively. The oscilloscope directly converts an analog signal into a digital signal by using a high-speed analog-to-digital conversion circuit (ADC), and then displays the digital signal, thereby being a direct time domain measuring instrument. The spectrum analyzer uses a superheterodyne structure, uses a mixer to perform frequency mixing on a measured signal and a scanned local oscillation signal in sequence to convert the measured signal and the scanned local oscillation signal to a fixed intermediate frequency, and measures the magnitude of the signal at the intermediate frequency, which is a typical frequency domain measuring instrument.

The oscilloscope requires that the sampling rate of the ADC is at least 2 times higher than the highest frequency component of the signal to be measured, and the nyquist sampling law is satisfied, and in practice, this requirement is often higher in order to satisfy the waveform display effect. The ADC sampling rate requirements become increasingly higher as the frequency of the signal under test continues to increase. At the same time, the large working bandwidth also causes the signal-to-noise ratio of the instrument to be greatly reduced. The spectrum analyzer utilizes the superheterodyne structure, can move the measured signal of different frequencies to the intermediate frequency in proper order and measure, therefore it can measure very high frequency signal. Meanwhile, the influence of the thermal noise of the system can be greatly reduced by adjusting the bandwidth of the intermediate frequency filter.

In conventional applications, as shown in fig. 1, a user typically measures the waveform and spectrum of a signal separately using an oscilloscope and a spectrum analyzer. Because the phase of the swept local oscillator signal of the traditional measurement method is random and cannot be measured in advance, when the measured signal is reconstructed, the relative phase of each frequency component cannot be calculated correctly. The invention adopts the local oscillator with repeatable phase sweep frequency, can measure the initial phase of the local oscillator signal in advance, and reconstructs the time domain waveform of the measured signal through a series of subsequent processing.

With the continuous development of digital processing technology in recent years, the time domain signal acquired by the oscilloscope can obtain the frequency spectrum information of the signal in an FFT mode. However, limited by the ADC sampling rate and the effect of wideband noise, the cost and difficulty of performance improvement increase with increasing frequency. However, the spectrum analyzer is limited in that the phase information of the measured signal cannot be accurately recovered, and therefore, the time domain waveform of the signal cannot be acquired. In some very specific, cost-prohibitive applications, there are spectrum stitching techniques. The technology utilizes a plurality of parallel down-conversion mixing links to simultaneously down-convert the frequency spectrum of a detected signal, and then utilizes a digital technology to recover and stitch the signal at an intermediate frequency. However, this method results in an increase in cost and volume by tens of times, so that it is considerably limited in flexibility and practicality.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a frequency spectrum scanning measuring device and a time domain waveform acquisition method.

In order to achieve the above object, the present invention provides a spectrum scanning measuring apparatus, including: the system comprises a low-pass filter, a synchronous control module, a frequency conversion link, an analog-to-digital converter and a digital signal processing module;

the low-pass filter is used for filtering an input high-frequency interference signal and preventing the high-frequency interference signal from entering the device in a mirror image mode to interfere the measurement of an effective input signal;

the synchronous control module is used for controlling the frequency conversion link, the analog-to-digital converter and the digital signal processing module to synchronously coordinate according to the triggering of the same clock;

the frequency conversion link comprises n +1 frequency mixers, n +1 band-pass filters, n fixed local oscillators and a phase repeatable swept local oscillator;

wherein, the 0 th order local oscillator is the repeatable frequency sweep local oscillator of phase place, and input signal and the 0 th order local oscillator signal all send into 0 th mixer, will produce following signal under this mixer's effect:

f_IF＝f_LO-f_RF

f_IM＝f_LO+f_RF

then, the 0 th-order band-pass filter will filter out the signal f_IMLeaving only the signal f_IF(ii) a Signal f according to the sampling frequency range of the ADC_IFThe last n mixers, the last n bandpass filters and the n fixed local oscillators form a multi-stage down-conversion link for frequency conversion processing, and the frequency of the intermediate frequency signal is reduced for many times in a cascading mode until the input requirement of the analog-to-digital converter is met;

the analog-to-digital converter performs analog-to-digital conversion on an input analog signal to convert the analog signal into a digital signal, and inputs the digital signal into the digital signal processing module;

the digital signal processing module carries out fast Fourier transform, phase recovery and amplitude and phase calibration on the input digital signal in sequence, so that the time domain waveform of the input signal is reconstructed.

The invention also provides a method for acquiring the signal time domain waveform by the frequency spectrum scanning measuring device, which is characterized by comprising the following steps:

(1) filtering the input high-frequency interference signal by using a low-pass filter, and preventing the high-frequency interference signal from entering a system in a mirror image mode to interfere the measurement of an effective input signal;

(2) the synchronous control module controls the frequency conversion link, the analog-to-digital converter and the digital signal processing module to trigger according to the same clock, so that the device is ensured to carry out frequency scanning measurement according to known and controllable time intervals;

(3) setting the scanning time interval of the phase repeatable sweep frequency local oscillator as T and the frequency spectrum scanning stepping interval as f₀；

(4) Carrying out frequency conversion processing on the frequency of the input signal for multiple times through the frequency conversion link, so that the frequency of the signal output by the frequency conversion link meets the input requirement of the analog-to-digital converter;

(5) the analog-to-digital converter performs analog-to-digital conversion on the input analog signal to convert the analog signal into a digital signal, and inputs the digital signal into the digital signal processing module;

(6) the digital signal processing module carries out Fast Fourier Transform (FFT) on the input digital signal, and distributes the calculated frequency values on a series of discrete sequences with intervals of delta f, wherein the delta f satisfies the following conditions:

wherein f is_sTaking the sampling rate of the ADC and M as the number of points of FFT conversion;

(7) and performing phase recovery on the phase of each frequency component after FFT

(7.1) compensating the delay time of the phase repeatable swept local oscillator

Setting the input signal to be tested and the nth phase repeatable sweep local oscillator signal nf₀In the frequency spectrum of the intermediate frequency signal obtained by mixing, the actual amplitude, phase and frequency values of the corresponding measured input signal at the m delta f frequency are respectively A_nm、

And f_nmThen, the frequency value of the input signal to be measured is represented by the phase repeatable swept local oscillator signal and the intermediate frequency signal as:

f_nm＝nf₀-mΔf

then, the measured input signal is actually represented as:

measuring the phase value of the measured input signal due to the effect of the time delay

Comprises the following steps:

therefore, the phase change caused by the lag time of the phase repeatable swept local oscillator should be compensated for, the actual phase of the input signal at this frequency being:

(7.2) compensating the local oscillator signal phase

N sweep local oscillator signal nf with phase capable of repeatedly sweeping local oscillator₀Has a phase of

The phase actual value is then expressed as:

(7.3) calculating the actual value of the phase of each frequency component after phase recovery;

(8) amplitude and phase calibration

(8.1) coarse calibration of amplitude and phase

(8.1.1) generating comb waves with known amplitudes and phases of frequency components by using a comb wave generator, wherein the comb waves are obtained by superposing multiple sine wave signals with sparse frequency intervals in a frequency domain, and the frequency range of the signals can cover the whole measurement range of the device; let the spectral interval of the sparse multiple sine wave signal be f₁N th₁The amplitude and phase of the subharmonic are respectively

And

(8.1.2) inputting the sparse multiple sine wave signal as a standard signal into the device for measurement, and performing the steps(7) The method carries out phase recovery on the phase calculation result, and sets the nth phase after recovery₁The amplitude and phase of the subharmonic are respectively

And

(8.1.3) comparing the recovered amplitude and phase with the known amplitude and phase of the input standard signal to obtain that the device is within the overall measurement range, n₁f₁The coarse calibration values for amplitude and phase at frequency are:

(8.2) Fine calibration of amplitude and phase

(8.2.1) generating a dense multiple sine wave signal having known amplitudes and phases of the respective frequency components by using an arbitrary wave generator, the frequency range of the signal being capable of covering a spectrum interval range of the above sparse multiple sine wave signal; setting the frequency starting point of the dense multiple sine wave signal generated in the 1 st coarse calibration frequency interval range as 1f₁Spectral interval of f₂N th₂The amplitude and phase of the subharmonic are respectivelyAnd

(8.2.2) inputting the dense multiple sine wave signal as a standard signal into the device for measurement, performing phase recovery on the phase calculation result according to the method in the step (7), and setting the n-th recovered signal₂The amplitude and phase of the subharmonic are respectivelyAnd

(8.2.3) comparing the recovered amplitude and phase with the known amplitude and phase of the input reference signal to obtain the device within a coarse calibration spectral interval, n₂f₂The fine calibration values for amplitude and phase at frequency are:

(8.3) interpolating the coarse calibration value in the entire measurement range of the system device by using the fine calibration value, and then, in the entire measurement range of the device, n₁f₁-n₂f₂The calibration values for amplitude and phase at frequency are:

wherein the content of the first and second substances,

represents taking n ₁1 hour, i.e. frequency f₁Amplitude and phase of (d);

then, after calibration, the actual values of the amplitude and phase of each frequency component are reconstructed as:

wherein:

nf₀-mΔf＝n₁f₁-n₂f₂

(9) and adding the reconstructed frequency components to reconstruct the time domain waveform of the input measured signal.

The invention aims to realize the following steps:

the invention relates to a frequency spectrum scanning measuring device and a time domain waveform acquisition method.A phase repeatable signal source is used as a sweep frequency local oscillator, and the local oscillator is controlled by software to carry out frequency coarse scanning with known scanning time interval; then, performing fast Fourier transform on the intermediate frequency signal obtained by the coarse scanning to realize frequency spectrum subdivision; then respectively restoring and calibrating the amplitude and the phase of the signal measurement value, wherein the restoration of the amplitude can be directly calibrated by using a standard signal and calibrated by a calibration value; the phase recovery firstly needs to recover the phase offset caused by non-real-time measurement of a frequency sweeping framework, secondly needs to eliminate the phase influence of an LO (local oscillator), and finally utilizes a comb wave transmitter and multiple sine waves to calibrate the phase of the whole system; after the frequency domain finishes the recovery of the signal amplitude and the phase, vector superposition is carried out on all the spectral components, and then the time domain waveform of the detected signal can be obtained.

Meanwhile, the frequency spectrum scanning measuring device and the time domain waveform obtaining method also have the following beneficial effects:

(1) when the waveform is obtained, compared with the traditional oscilloscope, the measuring device greatly reduces the requirement on the sampling frequency of the ADC, so that the accurate obtaining of the time domain waveform of a high-frequency and large-bandwidth signal can be realized by using the ADC with a low sampling rate;

(2) through the programming control of the FFT point number, the measuring device can realize the sweep frequency measurement of extremely narrow resolution bandwidth, and the advantage can greatly improve the signal-to-noise ratio of the instrument, thereby realizing the accurate measurement of large dynamic range signals.

Drawings

FIG. 1 is a schematic block diagram of a conventional spectral scanning measurement apparatus;

FIG. 2 is a functional block diagram of a spectral scanning measurement apparatus;

FIG. 3 is a flow chart of a method for acquiring a time domain waveform of a signal by a spectrum scanning measurement device;

FIG. 4 is a time domain waveform of an original input signal;

FIG. 5 is a measurement signal without phase recovery and calibration;

FIG. 6 is a time domain waveform of a signal after phase recovery but before phase calibration;

FIG. 7 is a graph comparing the signal waveform obtained by the present invention with the original measured signal magnitude spectrum;

FIG. 8 is a graph comparing the waveform of a signal acquired by the present invention with the phase spectrum of the original signal under test;

FIG. 9 is a graph comparing the time domain of the signal waveform obtained by the present invention with the original signal under test.

Detailed Description

The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.