阅读说明：本技术 脉冲调制信号载波频率测量系统及方法 (System and method for measuring carrier frequency of pulse modulation signal ) 是由 樊光辉 韩立群 于 2019-08-15 设计创作，主要内容包括：本发明提供了一种脉冲调制信号载波频率测量系统,包括前端电路、高速采集卡以及上位机,前端电路用于将被测信号和本地载波进行混频,并输出脉冲调制中频载波信号给高速采集卡；高速采集卡用于将采集的脉冲调制中频载波信号转换为数字信号,传输给上位机；上位机用于将采集到的数字信号进行基于过零判断和周期计数的频率测量算法。本发明将脉冲调制信号的载波频率测量放在上位机上实现,使得实现算法的装置整体架构更偏软件化,符合软件无线电的设计思路,简化硬件设计,使得硬件架构更加通用化,上位机软件算法设计更加灵活,优化信号频率测量过程中信号抖动噪声对测量结果的影响；利用周期测量法、过零检测、线性插值,提高频率测量的精度。(The invention provides a pulse modulation signal carrier frequency measuring system, which comprises a front-end circuit, a high-speed acquisition card and an upper computer, wherein the front-end circuit is used for mixing a measured signal with a local carrier and outputting a pulse modulation intermediate frequency carrier signal to the high-speed acquisition card; the high-speed acquisition card is used for converting the acquired pulse modulation intermediate frequency carrier signal into a digital signal and transmitting the digital signal to the upper computer; and the upper computer is used for carrying out a frequency measurement algorithm based on zero-crossing judgment and cycle counting on the acquired digital signals. The invention realizes the carrier frequency measurement of the pulse modulation signal on the upper computer, so that the whole structure of the device for realizing the algorithm is more software, accords with the design thought of software radio, simplifies the hardware design, makes the hardware structure more universal, has more flexible upper computer software algorithm design, and optimizes the influence of signal jitter noise on the measurement result in the signal frequency measurement process; the precision of frequency measurement is improved by utilizing a periodic measurement method, zero-crossing detection and linear interpolation.)

1. The utility model provides a pulse modulation signal carrier frequency measurement system which characterized in that, includes front end circuit, high-speed collection card and host computer, wherein:

the front-end circuit is used for mixing a detected signal with a local carrier and outputting a pulse modulation intermediate frequency carrier signal to the high-speed acquisition card;

the high-speed acquisition card is used for converting the acquired pulse modulation intermediate frequency carrier signal into a digital signal and transmitting the digital signal to the upper computer;

and the upper computer is used for carrying out a frequency measurement algorithm based on zero-crossing judgment and cycle counting on the acquired digital signals.

2. The system of claim 1, wherein the front-end circuitry comprises a programmable attenuator circuit, a protection circuit, and an intermediate frequency conditioning amplifier circuit, wherein:

the measured signal is mixed with the local carrier sequentially through the program-controlled attenuation circuit and the protection circuit to form an intermediate frequency signal, and the intermediate frequency signal is amplified through the intermediate frequency conditioning and amplifying circuit to form a pulse modulation intermediate frequency carrier signal and is output to the high-speed acquisition card.

3. The system according to claim 1, wherein the acquisition mode of the high speed acquisition card is a level triggered mode.

4. The system for measuring the carrier frequency of a pulse modulation signal according to claim 1, wherein the signal collected by the high-speed acquisition card is a bipolar single-frequency continuous sine wave signal.

5. A pulse modulated signal carrier frequency measurement method based on the pulse modulated signal carrier frequency measurement system according to any one of claims 1 to 4, characterized by comprising the steps of:

front-end circuit adjusting: the detected signal passes through a front-end circuit, is mixed with a local carrier wave, and outputs a pulse modulation intermediate frequency carrier signal to a high-speed acquisition card;

a signal acquisition step: the high-speed acquisition card is used for acquiring signals of the pulse modulation intermediate frequency carrier signals, converting the acquired signals into digital signals and transmitting the digital signals to the upper computer;

a signal processing step: and the upper computer performs frequency measurement algorithm processing based on zero-crossing judgment and cycle counting on the acquired digital signals.

6. The method of claim 5, wherein the frequency measurement algorithm comprises:

a zero crossing point detection step: carrying out zero crossing point detection judgment on the acquired signals;

and (3) calculating and recording: the first and last zero crossings are calculated and recorded and the carrier frequency is calculated.

7. The method of claim 6, further comprising the step of averaging: the results of multiple carrier frequency measurements are averaged.

8. The method of measuring a carrier frequency of a pulse modulated signal according to claim 6, wherein the zero-crossing point detecting step comprises:

setting the collected signal as buf [ k ], k is more than or equal to 1 and less than or equal to N, N is the total number of points of the data collected in the group, k is an index number, and the frequency of signal collection is fs;

and performing zero-crossing point traversal detection from the first data buf [1] of the buf [ k ], and determining a zero-crossing point when the detected data meets the conditions of buf [ k ] < 0, buf [ k +1] being more than or equal to 0 and buf [ k + t ] > 0, wherein t is more than or equal to 2 and t is an integer.

9. The method of claim 8, wherein the first and last zero-crossings are calculated and recorded as:

K1＝k1+buf[k1]/(buf[k1+1]-buf[k1])；

K2＝k2+buf[k2]/(buf[k2+1]-buf[k2])；

wherein: k1 is the first zero crossing index value and k2 is the last zero crossing index value.

10. The method of measuring a carrier frequency of a pulse modulated signal according to claim 9, wherein the carrier frequency freq is calculated as: freq ═ fs (CNT-1)/(K2-K1), where: CNT is the total number of all zero-crossings in the length of the collected data.

Technical Field

The invention relates to the technical field of signal testing, in particular to a system and a method for measuring the carrier frequency of a pulse modulation signal.

Background

The pulse modulation signal is a common signal form in electronic equipment such as radar communication, electronic countermeasure, airborne transponder and the like, and the pulse modulation is realized by controlling the on-off of a carrier signal through a long-period narrow pulse signal. Measurement of the carrier frequency of a pulse modulated signal is a common function of signal testing type instruments. Common frequency measurement methods include a frequency counting method, a period measurement method, a zero-crossing detection method and the like. The measurement methods are mainly realized on hardware, each measurement method has respective advantages and disadvantages, and the measurement method directly applied to carrier frequency measurement of pulse modulation signals has the disadvantages of insufficient measurement precision, sensitivity to signal noise jitter and the like.

Disclosure of Invention

In view of the defects in the prior art, the present invention provides a system and a method for measuring a carrier frequency of a pulse modulation signal.

The invention provides a system for measuring the carrier frequency of a pulse modulation signal, which comprises a front-end circuit, a high-speed acquisition card and an upper computer, wherein:

the front-end circuit is used for mixing a detected signal with a local carrier and outputting a pulse modulation intermediate frequency carrier signal to the high-speed acquisition card;

the high-speed acquisition card is used for converting the acquired pulse modulation intermediate frequency carrier signal into a digital signal and transmitting the digital signal to the upper computer;

and the upper computer is used for carrying out a frequency measurement algorithm based on zero-crossing judgment and cycle counting on the acquired digital signals.

Preferably, the front-end circuit includes a programmable attenuation circuit, a protection circuit, and an intermediate frequency conditioning and amplifying circuit, wherein:

the measured signal is mixed with the local carrier sequentially through the program-controlled attenuation circuit and the protection circuit to form an intermediate frequency signal, and the intermediate frequency signal is amplified through the intermediate frequency conditioning and amplifying circuit to form a pulse modulation intermediate frequency carrier signal and is output to the high-speed acquisition card.

Preferably, the acquisition mode of the high-speed acquisition card is a level trigger mode.

Preferably, the signal acquired by the high-speed acquisition card is a bipolar single-frequency continuous sine wave signal.

The invention provides a method for measuring the carrier frequency of a pulse modulation signal, which comprises the following steps:

front-end circuit adjusting: the detected signal passes through a front-end circuit, is mixed with a local carrier wave, and outputs a pulse modulation intermediate frequency carrier signal to a high-speed acquisition card;

a signal acquisition step: the high-speed acquisition card is used for acquiring signals of the pulse modulation intermediate frequency carrier signals, converting the acquired signals into digital signals and transmitting the digital signals to the upper computer;

a signal processing step: and the upper computer performs frequency measurement algorithm processing based on zero-crossing judgment and cycle counting on the acquired digital signals.

Preferably, the frequency measurement algorithm comprises:

a zero crossing point detection step: carrying out zero crossing point detection judgment on the acquired signals;

and (3) calculating and recording: the first and last zero crossings are calculated and recorded and the carrier frequency is calculated.

Preferably, the method further comprises an averaging step: the results of multiple carrier frequency measurements are averaged.

Preferably, the zero-crossing point detecting step includes:

setting the collected signal as buf [ k ], k is more than or equal to 1 and less than or equal to N, N is the total number of points of the data collected in the group, k is an index number, and the frequency of signal collection is fs;

and performing zero-crossing point traversal detection from the first data buf [1] of the buf [ k ], and determining a zero-crossing point when the detected data meets the conditions of buf [ k ] < 0, buf [ k +1] being more than or equal to 0 and buf [ k + t ] > 0, wherein t is more than or equal to 2 and t is an integer.

Preferably, the first and last zero-crossings are calculated and recorded as:

K1＝k1+buf[k1]/(buf[k1+1]-buf[k1])；

K2＝k2+buf[k2]/(buf[k2+1]-buf[k2])；

wherein: k1 is the first zero crossing index value and k2 is the last zero crossing index value.

Preferably, the calculated carrier frequency freq is: freq ═ fs (CNT-1)/(K2-K1), where: CNT is the total number of all zero-crossings in the length of the collected data.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention utilizes the frequency mixing technology and the high-speed sampling technology to measure the carrier frequency of the pulse modulation signal on the upper computer, so that the whole structure of the device for realizing the algorithm is more software, the design idea of software radio is met, the hardware design is simplified, the hardware structure is more universal, and the algorithm design of the upper computer software is more flexible.

2. The invention can optimize the influence of signal jitter noise on the measurement result in the signal frequency measurement process;

the invention comprehensively utilizes the periodic measurement method, the zero-crossing detection and the linear interpolation, thereby greatly improving the precision of frequency measurement.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is an overall system diagram of a pulse modulated signal carrier measurement system;

FIG. 2 is a schematic diagram of a signal acquisition process;

FIG. 3 is a schematic diagram of zero crossing point determination;

FIG. 4 is a schematic diagram of fractional-level index calculation.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

As shown in fig. 1 to 4, a system and a method for measuring a carrier frequency of a pulse modulation signal according to the present invention includes a front-end circuit, a high-speed acquisition card and an upper computer, wherein the front-end circuit is configured to mix a signal to be measured with a local carrier and output a pulse modulation intermediate frequency carrier signal to the high-speed acquisition card; the high-speed acquisition card is used for converting the acquired pulse modulation intermediate frequency carrier signal into a digital signal and transmitting the digital signal to the upper computer; and the upper computer is used for carrying out a frequency measurement algorithm based on zero-crossing judgment and cycle counting on the acquired digital signals. The front-end circuit comprises a program-controlled attenuation circuit, a protection circuit and an intermediate frequency conditioning and amplifying circuit, a detected signal is mixed with a local carrier sequentially through the program-controlled attenuation circuit and the protection circuit to form an intermediate frequency signal, and the intermediate frequency signal is amplified through the intermediate frequency conditioning and amplifying circuit to form a pulse modulation intermediate frequency carrier signal and is output to the high-speed acquisition card.

Because the carrier frequency of the detected signal is usually high, a front-end circuit is arranged before sampling, the high-frequency carrier and the local carrier are mixed and converted into a low-frequency intermediate-frequency signal, and a protection circuit, an intermediate-frequency conditioning and amplifying circuit and the like are further arranged in the front-end circuit and used for conditioning the signal to be within a safe and reasonable level range. The front-end circuit outputs a lower frequency pulse modulated intermediate frequency carrier signal.

The pulse modulation intermediate frequency carrier signal is input to the signal input end of the hardware high-speed acquisition card, and the signal acquisition frequency of the high-speed acquisition card is several times of the intermediate frequency carrier signal frequency. The sampling mode is level triggering, and after the sampling mode is triggered, the length of the collected signal does not exceed the length of one pulse period. Therefore, the signals acquired by the high-speed acquisition card each time are bipolar single-frequency continuous sine wave signals, are converted into digital signals and then are transmitted to an upper computer for processing. The signal acquisition process is shown in figure 2.

And the upper computer performs a frequency measurement algorithm based on zero-crossing judgment and cycle counting on the digital single-frequency continuous sine wave signals acquired by triggering. The collected signals are assumed to be buf [ k ], k is more than or equal to 1 and less than or equal to N, N is the total point number of the collected data of the group, and k is an index number. The frequency of signal acquisition is fs. The algorithm comprises the following specific steps:

step 1, zero crossing point (integer level) detection:

zero-crossing point traversal detection is performed starting from the first data buf [1] of buf [ k ]. And when the data are detected to meet the conditions of buf [ k ] < 0, buf [ k +1] > 0 and buf [ k + t ] > 0, determining a zero-crossing point. And t is more than or equal to 2, a zero crossing point is preliminarily judged according to the buf [ k ] and the buf [ k +1], and the zero crossing point is confirmed again by utilizing the buf [ k + t ], so that the accuracy of judging the zero crossing point is improved. the t can be set according to the noise or signal jitter level of an application system, the larger the noise or signal jitter is, the larger the value of t in a reasonable range can be taken, and the accuracy of zero crossing point judgment is further improved by the processing. The principle is shown in fig. 3, and signal small-amplitude jitter occurs in some parts of the signal. Two groups of 4 continuous points are observed, and in the previous group of 4 points, if only the 1 st point and the 2 nd point are judged, or if t is 1, the continuous 3 points are judged, the zero-crossing point misjudgment obviously occurs. If t is 2, misjudgment cannot occur at the first group of 4 points, and the zero-crossing point can be accurately judged at the second group of 4 points.

In the zero crossing point searching process, the data to be recorded are as follows: the first zero-crossing index k1 value, buf [ k1] and buf [ k1+1] values; the last zero crossing index k2 value, buf [ k2] and buf [ k2+1] values; the total number of zero-crossings CNT within the length of the acquired data.

Two points need to be explained here:

1. the judgment with the zero value as the threshold is only an example of a special value situation, when the design algorithm is practically applied, other thresholds can be set according to needs, and the judgment of the times of passing the threshold is performed, and the method is the same as the judgment of the zero crossing times.

2. Here, three points are used for the determination of the over-threshold, and the third point is a duplicate confirmation effect. When the algorithm thought is actually applied, the number of times of confirmation can be increased according to the actual situation.

Step 2, calculating and recording the first and the last zero-crossing points (decimal order) respectively as follows:

K1＝k1+buf[k1]/(buf[k1+1]-buf[k1])

K2＝k2+buf[k2]/(buf[k2+1]-buf[k2])；

the calculation utilizes the property that sin (x) is approximately equal to x when x is close to 0, and linear calculation is carried out to obtain zero-crossing point indexes of decimal order. The processing well overcomes the error caused by the fact that the conventional cycle measurement counting method can only record integral multiple signal cycles, and effectively improves the accuracy of frequency calculation results. The calculation schematic is shown in fig. 4.

And step 3: the carrier frequency freq is calculated as: freq ═ fs (CNT-1)/(K2-K1);

and 4, step 4: to further improve accuracy, if necessary, multiple measurements may be averaged:

where i is the result of the ith acquisition measurement, M times are measured, and 1. ltoreq. i.ltoreq.M.

The test object aimed at by the algorithm calculation step described in the technical scheme can be of other signal types, not only pulse modulation signals, but also single-frequency periodic sinusoidal signals, square wave signals, triangular wave signals and the like. As well as specific embodiments of the algorithm of the present invention.

According to another embodiment provided by the invention, the pulse modulation signal carrier frequency measurement circuit comprises a front-end circuit, a high-speed acquisition circuit and a DSPDSP or FPGA or ARM, wherein: the front-end circuit converts the high-frequency pulse modulation signal into an intermediate-frequency pulse modulation signal, and under a certain condition, the front-end circuit is not necessary; the high-speed acquisition circuit converts the intermediate frequency pulse modulation signal into a digital intermediate frequency pulse modulation signal through an analog-to-digital conversion chip and transmits the digital signal to a DSP (digital signal processor), an FPGA (field programmable gate array) or an ARM (advanced RISC machine); and the DSP or the FPGA or the ARM carries out frequency calculation of the carrier frequency according to the technical scheme according to the collected data.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.