WO2017173913A1

WO2017173913A1 - Method and circuit for forming pulse stream during sparse sampling of ultrasonic signal

Info

Publication number: WO2017173913A1
Application number: PCT/CN2017/076691
Authority: WO
Inventors: 宋寿鹏; 江洲
Original assignee: 江苏大学
Priority date: 2016-04-08
Filing date: 2017-03-15
Publication date: 2017-10-12
Also published as: CN105738885A; CN105738885B

Abstract

Disclosed are a method and a circuit for forming a pulse stream during sparse sampling of an ultrasonic signal. The method comprises: generating, by a local oscillator, an oscillating signal having a frequency double a center frequency of an ultrasonic signal S(t); dividing the oscillating signal by two and performing modulation and mixing on the respective signals and the S(t); passing two modulated and mixed signals through a low-pass filter to generate two output signals; and squaring the two output signals respectively, adding the squares, and calculating a square root of the sum, so as to obtain a final output signal A(t), wherein A(t) is a pulse stream obtained by detecting the ultrasonic signal S(t). The circuit comprises: a local oscillating module (S1), an orthogonal mixing module (S2), a low-pass filtering module (S3), and a modulo operation module (S4). The method and the circuit of the present invention are applicable to a sparse sampling system for an ultrasonic signal based on finite rate of innovation, so as to achieve sparse sampling at a rate much lower than the conventional Nyquist sampling rate, and thus resolving the issue in conventional sampling methods of overly large amounts of data, while retaining original signals and information, thereby enabling real-time formation of an ultrasonic pulse stream.

Description

Method and circuit for forming pulse flow in ultrasonic signal sparse sampling

Technical field

The invention belongs to the technical field of ultrasonic signal sparse sampling, and particularly relates to a method for forming a pulse stream in a sparse sampling of an ultrasonic signal based on a limited innovation rate and a hardware front end physical realization circuit.

Background technique

Ultrasonic testing is an important non-destructive testing method. In order to improve the detection efficiency and improve the detection rate and imaging resolution of internal defects of materials, multi-sensor array structure, high detection frequency and long-time detection are often used. Obtain rich ultrasound echo information of the target body. However, the unfavorable consequence is that massive detection data is present, which brings great difficulties to the acquisition, transmission, storage and real-time processing of signals. In order to solve this problem, researchers explored a new data sampling method other than the conventional Shannon-Nyquist sampling method to reduce the amount of data collected without losing or losing the target information as little as possible.

In recent years, new methods have been emerging around reducing the sampling rate of ultrasonic signals and reducing the amount of data collected. Its representative sampling methods mainly include compression sensing technology and limited innovation rate sampling technology. These methods are all sparse sampling methods of signals. Although these methods can effectively reduce the sampling rate of the signal, at present, it mainly stays in the theoretical analysis stage, theoretically realizes the sparse sampling of the signal, and verifies that after the signal is sampled by these sampling methods, the signal is Useful information can be rebuilt. The emergence of Compressive Sensing (CS) theory breaks the limitation of conventional Nyquist sampling on the lowest sampling frequency, which lays a foundation for low-speed acquisition of high-speed signals. At present, CS theory has been widely used in signal acquisition in the fields of communication and wireless sensor networks. The hardware implementation models mainly include Analog-to-Information Convertor (AIC) and Modulated Wideband Conversion (MWC). The concept of the new interest rate comes from the FRI (Finite Rate of Innovation) theory, which can be sampled for a specific pulse or pulse stream signal. It was first proposed by Vetterli et al. The FRI theory is a sampling signal scheme combining traditional Shannon sampling theory and sub-Nyquist sampling, and is collected at a new interest rate. Signals with FRI properties can be represented by the known delay and amplitude of the pulse, thus reducing the signal sampling rate and reducing the amount of data. The ultrasonic detection echo signal can be regarded as a superposition of a series of Gaussian pulse signals, so it has the FRI signal property, and the FRI theory can be used for signal acquisition and reconstruction. The FRI sampling method for ultrasonic signals was first published in 2011 by Israel's YC. Eldar et al. (Innovation rate sampling of pulse streams with Application to ultrasound imaging, IEEE Transactions on Signal Process, 2011, 59(4), 1827–1842). Since the original ultrasound signal does not belong to the FRI signal, FRI sampling cannot be performed directly. A pulse stream must be formed from the original detection signal to perform limited Xinxin rate sparse sampling.

The existing ultrasonic pulse stream extraction method is mainly realized by a software algorithm, that is, the original signal is first collected at an acquisition rate higher than the Nyquist frequency, and then the acquired digital signal is processed by using a demodulation algorithm to obtain Pulse stream signal. According to the data (Lu Zhenkun. Parameterized ultrasonic echo model and its parameter estimation [D]. South China University of Technology. 2013; Lin Weiyi. Ultrasonic low-frequency imaging based on FRI [D]. South China University of Technology. 2013; Cao Wen, Liu Chunmei, Hu Li.A digital quadrature detection method for ultrasonic echo signals and FPGA implementation[J].Journal of Southwest University of Science and Technology.2006,21.3, 56-60), the current software extraction methods for ultrasonic pulse flow mainly include Network detection method, Hilbert transform method and quadrature demodulation method. The software method extracts the signal envelope with high precision, flexibility and versatility. However, such methods are based on the traditional Shannon sampling theorem, which requires conventional Nyquist sampling of the original signal, which is not a physical implementation of sparse sampling.

In order to make the sparse sampling method be used in practice, the physical realization of the pulse stream must be fundamentally solved. The present invention is directed to an ultrasonic signal, and a physical forming method and circuit for the ultrasonic pulse stream are proposed.

Summary of the invention

In order to solve the problem that the existing software algorithm cannot realize the direct physical sampling of the ultrasonic signal FRI, the present invention proposes an ultrasonic pulse flow physical forming method and circuit based on the orthogonal demodulation principle, and uses the analog circuit to realize the direct extraction of the pulse stream from the ultrasonic signal. signal. The method is easy to implement, has high demodulation accuracy and does not require an accurate carrier frequency. The technical solution for implementing the present invention is as follows:

A method for pulse formation in ultrasonic signal sparse sampling, comprising the following steps:

Step 1: The local oscillator generates a square wave oscillating signal F _LO (t) of a fixed frequency, and the oscillating frequency f _c satisfies: f _c = 2f ₀ ; wherein f ₀ is the center frequency of the ultrasonic echo signal;

Step 2, the oscillating signal F _LO (t) in step 1 is divided by two to form two square wave carrier signals with equal amplitude, same frequency and phase difference of 90 degrees, respectively F ₁ (t), F ₂ (t);

Step 3, multiplying and receiving the ultrasonic echo signals S(t) having the center frequency f ₀ and the two square wave signals F ₁ (t) and F ₂ (t) in step 2, respectively, The ultrasonic echo signal is spectrally shifted to form two orthogonal signals I(t), Q(t) including low frequency components and higher harmonic components;

Step 4, performing low-pass filtering on the two orthogonal signals I(t) and Q(t) in step 3, filtering out higher harmonic components, and forming two low-frequency component signals I'(t), Q' (t);

Step 5, performing modulo operation on the two orthogonal low-frequency component signals I'(t), Q'(t) in step 4, and acquiring an ultrasonic pulse stream signal A(t) for FRI sparse sampling, The method comprises: squarely adding the two orthogonal low-frequency component signals I′(t) and Q′(t), and performing square root operation on the operation result to obtain an ultrasonic pulse stream signal A(t).

Further preferably, the step 2 further comprises: setting a frequency difference between the actual carrier signal frequency and the actual ultrasonic echo signal center frequency to be Δf, and establishing the F ₁ (t), F ₂ (t) Fourier with the ultrasonic echo signal as a reference The series expansion is as follows:

Where K is the carrier amplitude coefficient, n = 1, 3, 5, ....

Further preferably, the step 3 further comprises: considering the ultrasonic echo signal S(t) as a Gaussian pulse stream signal amplitude-modulated by the probe center frequency signal, and establishing the following mathematical expression:

Where L is the number of echoes;

Is the amplitude coefficient of the echo;

Is the echo bandwidth factor; τ is the arrival time of the echo; f ₀ is the center frequency of the ultrasonic echo signal;

Is the initial phase; A(t) represents a Gaussian pulse stream signal with a pulse number of L,

Further preferably, the parameters of the low pass filter in step 4 are determined according to the following formula:

Where f ₀ represents the center frequency of the ultrasonic echo signal; f _p represents the cut-off frequency of the filter pass band; f _s represents the cut-off frequency of the filter stop band; BW _A(t) represents the bandwidth of the ultrasonic pulse flow signal A(t).

In order to implement the above method on the hardware underlayer, the present invention also proposes a pulse forming circuit for ultrasonic signal sparse sampling, comprising: a local oscillation module, a quadrature mixing module, a low-pass filtering module, and a modulo operation module; The output of the local oscillation module is connected to the orthogonal mixing module after being divided by two. The orthogonal mixing module, the low-pass filtering module, and the modulo computing module are sequentially connected;

The local oscillation module is configured to generate a square wave signal, the square wave signal frequency f _c = 2f ₀ , f ₀ is the ultrasonic echo signal center frequency; the square wave signal is divided by two to generate a frequency f ₀ , Two square wave carrier signals F ₁ (t), F ₂ (t) with a phase difference of 90 degrees;

The quadrature mixing module is configured to multiply and mix the ultrasonic echo signals with the two carrier signals F ₁ (t) and F ₂ (t) to obtain two orthogonal signals I(t) and Q. (t);

The low pass filtering module is configured to filter out higher harmonic parts of the two orthogonal signals output by the quadrature mixing module to obtain low frequency signals I'(t), Q'(t);

The modulo operation module is configured to extract a DC component in the two signals output by the low-pass filter module, and synthesize the pulse stream signal to obtain an ultrasonic pulse stream signal A(t) for FRI sparse sampling.

Further preferably, the local oscillation module uses a varactor diode SVC321 and a high-speed CMOS Schmitt inverter 74HC14 to form a voltage-controlled square wave oscillating circuit, and the voltage-dividing circuit provides a control voltage of 0 to 10V, and is added by a DC bias resistor R1. Connect to the varactor diode and isolate the control voltage from the CMOS Schmitt inverter input with a large capacitor C1. The varactor diode capacitance varies from 20pF to 400pF, and the resistor R2 and the varactor diode VC1 are timed. The constant determines the frequency f _{c of the} oscillating signal.

Further preferably, the quadrature mixing module is implemented by using an integrated quadrature demodulation chip RF2713, and the signal F _LO (t) generated by the local oscillation module is input to the LO input pin of the RF2713 through the capacitor C2 in an AC coupling manner. The RF2713 internally includes a digital frequency divider that divides F _LO (t) into two square wave carrier signals with a phase difference of 90 degrees; the ultrasonic echo signal S(t) is AC coupled through capacitor C3. The method is input into RF2713, and is mixed by two internal Gilbert mixing units and two square wave carrier signals respectively, and the two output signals I(t) and Q(t) after mixing are respectively passed through capacitors C7 and C8. Output in AC coupling.

In a further preferred solution, the low-pass filter module comprises a third-order linear phase low-pass filter of a SallenKey structure by an integrated operational amplifier chip AD847 and a plurality of resistor capacitors.

In a further preferred embodiment, the modulo operation module includes a two-way square operation circuit, an add-on operation circuit, and an open-square root operation circuit, and the two-way square operation circuits are all connected to the addition operation circuit, and the addition operation circuit and The square root computing circuit is connected;

The square operation circuit and the square root operation circuit are both realized by an integrated analog multiplier chip AD734 and a plurality of resistor capacitors, and the adder circuit is composed of an integrated op amp chip AD847 to form an in-phase adder.

The beneficial effects of the invention:

1. The present invention is different from the existing ultrasonic signal FRI sampling method for extracting ultrasonic pulse flow by software method, and the ultrasonic pulse flow signal is directly extracted by the hardware circuit, and is suitable for the ultrasonic signal FRI sampling system.

2. The proposed ultrasonic pulse flow physical formation method based on the orthogonal demodulation principle can accurately extract the pulse flow signal from the original ultrasonic echo signal.

3. The method allows the carrier frequency to have a certain deviation from the center frequency of the actual echo signal, which reduces the design complexity.

4. The designed ultrasonic pulse stream physically forms a circuit, and the quadrature demodulation process is realized by the analog circuit built by the integrated chipset, and the circuit structure is simple and easy to implement.

5. The hardware implementation of the pulse stream is the key to the physical realization of the ultrasonic signal sparse sampling. While ensuring the information integrity in the signal, the data collection amount can be greatly reduced, and the problem that the conventional sampling method has too large data amount is solved.

DRAWINGS

1 is a schematic diagram of a method for physically forming an ultrasonic pulse stream in the present invention;

2 is an actual ultrasonic echo signal in an embodiment of the present invention;

3 is an ultrasonic pulse stream signal extracted by an existing software method;

4 is an ultrasonic pulse stream signal extracted by an actual circuit according to an embodiment of the present invention;

5 is a schematic circuit diagram of a local oscillation module according to an embodiment of the present invention;

6 is a schematic circuit diagram of a quadrature mixing module according to an embodiment of the present invention;

7 is a schematic circuit diagram of a low pass filter module according to an embodiment of the present invention;

FIG. 8 is a schematic circuit diagram of a modulo operation module according to an embodiment of the present invention.

Marked in the figure: S1-local oscillation module, S2-orthogonal mixing module, S3-low-pass filter module, S4-modulo operation module.

detailed description

The technical solutions of the present invention are further described below in conjunction with the accompanying drawings and embodiments.

The actual ultrasonic echo signal used in this embodiment is as shown in FIG. The center frequency of the ultrasonic probe is 5 MHz, and the actual measured echo center frequency f ₀ is about 3.5 MHz.

The frequency f _c of the oscillation output signal F _LO (t) of the local oscillator is determined according to the center frequency of the actual echo signal:

f _c =2f ₀ =7MHz

Since the actual ultrasonic echo signal center frequency f _{0 is} affected by external factors, a certain frequency fluctuation will occur, and the oscillation signal F _LO (t) has a certain limit between the theoretical calculation value and the theoretical calculation value due to the performance limitation of the analog circuit. Frequency deviation. Therefore, there is a certain frequency difference Δf between the actual carrier signal frequency generated by the frequency division and the actual echo signal center frequency. Taking the echo signal as a reference, the carrier signal frequency is (f ₀ +Δf), and the Fourier series expansion of the two carrier signals F ₁ (t) and F ₂ (t) are:

Where K is the carrier amplitude coefficient, n = 1, 3, 5, ....

The ultrasonic echo signal S(t) can be regarded as a Gaussian pulse stream signal amplitude-modulated by the probe center frequency signal, which can be approximated by the following mathematical model:

Where L is the number of echoes;

Is the amplitude coefficient of the echo;

Is the echo bandwidth factor; τ is the arrival time of the echo; f ₀ is the center frequency of the echo signal;

Multiplying the ultrasonic echo signal S(t) by the two carrier signals F ₁ (t), F ₂ (t) to obtain two orthogonal signals I(t), Q(t):

Therefore, the two signals I(t) and Q(t) formed after the mixing respectively contain low frequency components.

And higher harmonic components with a frequency of 2f ₀ + Δf or more.

Low-pass filtering filters out higher-order harmonic components with frequencies above 2f ₀ +Δf in I(t) and Q(t), leaving only low-frequency components, resulting in low-frequency quadrature signals I'(t), Q' (t).

The setting of the filter parameters can be determined according to the following formula:

After filtering out the high frequency component, two low frequency quadrature signals I'(t), Q'(t) are formed, and the expression is:

For I'(t), Q'(t) are squared and added separately, and then the square root operation is performed:

The ultrasonic pulse stream signal A(t) is thus obtained.

It can be seen that by reasonably designing the parameters of the filter, the error introduced by the frequency difference Δf can be eliminated in the modulo operation. Therefore, the method allows a certain frequency difference between the carrier signal frequency and the echo signal center frequency, which relaxes the limitation of the design of the hardware circuit.

As shown in FIG. 1, it is a schematic diagram of a physical formation method of ultrasonic pulse flow in the present invention. Including: local oscillation a module S1, a quadrature mixing module S2, a low-pass filtering module S3, and a modulo operation module S4; the output of the local oscillation module is connected to the orthogonal mixing module after being divided by two, the orthogonal mixing The frequency module, the low-pass filter module, and the modulo operation module are sequentially connected;

The local oscillation module S1 in the present invention is as shown in FIG. A square wave oscillating signal having a frequency twice the center frequency of the ultrasonic echo signal is generated. The module uses a varactor diode SVC321 and a high speed CMOS Schmitt inverter 74HC14 to form a voltage controlled square wave oscillating circuit. A voltage of 0 to 10 V is supplied from the voltage dividing circuit, and is applied to the varactor through a DC bias resistor R1, and the control voltage is isolated from the input end of the CMOS chip by the large capacitor C1. The capacitance of the varactor diode ranges from about 20pF to 400pF. The time constant of the resistor R2 and the capacitance VC1 of the varactor determines the frequency of the oscillating signal. The oscillating frequency f _c can be approximated by the following equation:

The orthogonal mixing module S2 in the present invention is as shown in FIG. The local oscillation signal F _LO (t) is divided by two to form two square wave carrier signals with a phase difference of 90 degrees, and the original ultrasonic signal is mixed with the two carrier signals to output two orthogonal signals I(t). Q(t). The module uses the integrated quadrature demodulation chip RF2713 to achieve its function. The local oscillating signal F _LO (t) is ac-coupled to the LO input pin of the RF2713 via capacitor C2. It internally includes a digital divider that divides F _LO (t) by two to a phase difference of 90. Square wave carrier signal. The ultrasonic echo signal S(t) is input to the RF2713 by means of a capacitor C3 in an AC-coupled manner, and is separately mixed with the two carrier signals by an internal two-way Gilbert mixing unit. The two output signals I(t) and Q(t) are outputted by AC coupling through capacitors C7 and C8, respectively.

The low pass filter module S3 in the present invention is as shown in FIG. Used to filter out the input of the quadrature mixing module S2 The two orthogonal signals I(t), Q(t) are the higher harmonic components. The module includes two filtering circuits with the same parameters, as shown in (a) and (b), respectively filtering the I(t), Q(t). Each channel uses an integrated operational amplifier chip AD847 to form a third-order linear phase low-pass filter of the SallenKey structure.

The modulo operation module S4 in the present invention is as shown in FIG. It is used to extract the DC component of the two signals outputted by the S3 low-pass filter module, and synthesize the pulse stream signal. The module includes two square operation circuits, one addition circuit and an square root operation circuit. The square operation and the square root operation circuit are composed of an integrated analog multiplier chip AD734, and the addition circuit uses an integrated operational amplifier chip AD847 to form an in-phase adder.

The ultrasonic pulse flow signal extracted from the ultrasonic echo signal shown in FIG. 2 by the ultrasonic pulse flow physical formation method and circuit proposed by the present invention is as shown in FIG. 4. 3 is an ultrasonic pulse stream signal extracted from the ultrasonic echo signal shown in FIG. 2 using a conventional quadrature demodulation software method. In the existing pulse stream formation algorithm, the orthogonal demodulation algorithm has the highest precision, which can meet the waveform requirements of the pulse stream in the sparse sampling of ultrasonic signals. It can be seen from the comparison between FIG. 3 and FIG. 4 that the pulse stream extracted by the hardware circuit of the present invention is very close to the pulse stream waveform extracted by the orthogonal demodulation algorithm, and can satisfy the waveform of the pulse stream in the hardware sparse sampling. Claim. Moreover, the existing algorithm needs to first obtain the signal according to the conventional sampling, and then form the pulse flow through the algorithm, thereby realizing the direct hardware formation of the pulse flow, and has real-time performance. The invention is the key to physically achieving sparse sampling of ultrasonic signals.

It should be understood that, although the present specification is described in terms of embodiments, not every embodiment includes only one independent technical solution, and those skilled in the art should have the specification as a whole, and the technical solutions in the respective embodiments may also be combined as appropriate. Other embodiments that can be understood by those skilled in the art are formed.

The series of detailed descriptions set forth above are merely illustrative of the possible embodiments of the present invention, and are not intended to limit the scope of the present invention. Changes are intended to be included within the scope of the invention.

Claims

A method for forming a pulse stream in ultrasonic signal sparse sampling, comprising the steps of:

Step 1: The local oscillator generates a square wave oscillating signal F LO (t) of a fixed frequency, and the oscillating frequency f c satisfies: f c = 2f 0 ; wherein f 0 is the center frequency of the ultrasonic echo signal;

Step 2, the oscillating signal F LO (t) in step 1 is divided by two to form two square wave carrier signals with equal amplitude, same frequency and phase difference of 90 degrees, respectively F 1 (t), F 2 (t);

Step 3, multiplying and receiving the ultrasonic echo signals S(t) having the center frequency f 0 and the two square wave signals F 1 (t) and F 2 (t) in step 2, respectively, The ultrasonic echo signal is spectrally shifted to form two orthogonal signals I(t), Q(t) including low frequency components and higher harmonic components;

Step 4, performing low-pass filtering on the two orthogonal signals I(t) and Q(t) in step 3, filtering out higher harmonic components, and forming two low-frequency component signals I'(t), Q' (t);

Step 5, performing modulo operation on the two orthogonal low-frequency component signals I'(t), Q'(t) in step 4, and acquiring an ultrasonic pulse stream signal A(t) for FRI sparse sampling, Specifically, the modulo operation includes: square-adding the two orthogonal low-frequency component signals I′(t) and Q′(t), and performing square root operation on the operation result to obtain an ultrasonic pulse stream signal A ( t).
The method for forming a pulse stream in an ultrasonic signal sparse sampling according to claim 1, wherein the step 2 further comprises: setting the frequency difference between the actual carrier signal frequency and the actual ultrasonic echo signal center frequency to Δf to the ultrasound The echo signal is used as a reference, and the Fourier series expansion of F 1 (t) and F 2 (t) is established as follows:

Where K is the carrier amplitude coefficient, n = 1, 3, 5, ....
The method for forming a pulse stream in ultrasonic signal sparse sampling according to claim 1, wherein the step 3 further comprises: treating the ultrasonic echo signal S(t) as amplitude modulation by the probe center frequency signal. The Gaussian pulse stream signal and establishes the following mathematical expression:

Where L is the number of echoes;
Is the amplitude coefficient of the echo;
Is the echo bandwidth factor; τ is the arrival time of the echo; f 0 is the center frequency of the ultrasonic echo signal;
Is the initial phase; A(t) represents a Gaussian pulse stream signal with a pulse number of L,
The method for forming a pulse stream in ultrasonic signal sparse sampling according to claim 1, wherein the parameter of the low-pass filter in step 4 is determined according to the following formula:

Where f 0 represents the center frequency of the ultrasonic echo signal; f p represents the cut-off frequency of the filter pass band; f s represents the cut-off frequency of the filter stop band; BW A(t) represents the bandwidth of the ultrasonic pulse flow signal A(t).
A circuit for forming a pulse stream in an ultrasonic signal sparse sampling, comprising: a local oscillation module S1, a quadrature mixing module S2, a low-pass filtering module S3, a modulo operation module S4, and an output of the local oscillation module After being divided by two, the orthogonal mixing module is connected, and the orthogonal mixing module, the low-pass filtering module, and the modulo computing module are sequentially connected;

The local oscillation module is configured to generate a square wave signal, the square wave signal frequency f c = 2f 0 , f 0 is the ultrasonic echo signal center frequency; the square wave signal is divided by two to generate a frequency f 0 , Two square wave carrier signals F 1 (t), F 2 (t) with a phase difference of 90 degrees;

The quadrature mixing module is configured to multiply and mix the ultrasonic echo signals with the two carrier signals F 1 (t) and F 2 (t) to obtain two orthogonal signals I(t) and Q. (t);

The low pass filtering module is configured to filter out higher harmonic parts of the two orthogonal signals output by the quadrature mixing module to obtain low frequency signals I'(t), Q'(t);

The modulo operation module is configured to extract a DC component in the two signals output by the low-pass filter module, and synthesize the pulse stream signal to obtain an ultrasonic pulse stream signal A(t) for FRI sparse sampling.
The circuit for forming a pulse stream in ultrasonic signal sparse sampling according to claim 5, wherein the local oscillation module comprises a varactor diode SVC321 and a high speed CMOS Schmitt inverter 74HC14 to form a voltage controlled square wave oscillation. The circuit is provided with a 0~10V control voltage from the voltage dividing circuit, and is applied to the varactor through the DC bias resistor R1, and the control voltage is isolated from the input end of the CMOS Schmitt inverter by the large capacitor C1, and the varactor diode is electrically connected. The capacity varies from 20 pF to 400 pF, and the time constant of the resistor R2 and the capacitance VC1 of the varactor determines the frequency f c of the oscillating signal.
The circuit for forming a pulse stream in the ultrasonic signal sparse sampling according to claim 5, wherein the orthogonal mixing module is implemented by using an integrated quadrature demodulation chip RF2713, and the signal generated by the local oscillation module is F LO (t) is ac-coupled to the LO input pin of RF2713 via capacitor C2. The RF2713 internally includes a digital divider that divides F LO (t) by two to a phase difference of 90 degrees. The square wave carrier signal; the ultrasonic echo signal S(t) is input to the RF2713 by means of the capacitor C3 in an AC coupling manner, and is separately mixed by the internal two-way Gilbert mixing unit and the two square wave carrier signals, after mixing The two output signals I(t) and Q(t) are outputted by AC coupling through capacitors C7 and C8, respectively.
The circuit for forming a pulse stream in ultrasonic signal sparse sampling according to claim 5, wherein the low-pass filter module comprises a third-order linear phase low-pass of the SallenKey structure by an integrated operational amplifier chip AD847 and a plurality of resistor capacitors. filter.
The circuit for forming a pulse stream in ultrasonic signal sparse sampling according to claim 5, wherein the modulo operation module comprises two square operation circuits, one add operation circuit and one open square root operation circuit, Two square operation circuits are connected to the addition circuit, and the addition circuit is connected to the square root operation circuit;

The square operation circuit and the square root operation circuit are both realized by an integrated analog multiplier chip AD734 and a plurality of resistor capacitors, and the adder circuit is composed of an integrated op amp chip AD847 to form an in-phase adder.