CN101147686B - Method and device for synthesizing simulation wave beam in continuous wave doppler modular - Google Patents

Abstract

A method and device for synthesizing analog beams in a continuous wave Doppler module, the device includes a delay line LC network composed of an inductance and a capacitor, and is connected in series at the input end of the delay line LC network for processing input signals Resistor for amplitude compensation. The multi-channel voltage signal output by the low-noise amplifier is compensated by the resistance connected in series with the delay line, and the compensated signal is added to the LC network of the delay line from different taps for signal delay and signal accumulation, and finally in the LC network The output terminal outputs the beamforming signal. The device of the present invention has the advantages of low cost, small size, good consistency of continuous wave echo amplitude of each channel, etc. The method and device of the present invention are suitable for ultrasonic diagnostic systems, especially for portable ultrasonic diagnostic systems requiring small volume.

Description

Method and device for synthesizing analog beams in continuous wave Doppler module

technical field

The invention relates to a signal processing method and device in a medical ultrasonic diagnostic system, in particular to a method and a device for combining beams of continuous wave signals in the ultrasonic diagnostic system by using a reverse application delay line. The method and device of the present invention are especially suitable for ultrasonic diagnostic systems, especially portable ultrasonic diagnostic systems that require small volume, and the beam synthesis of B images of low-end ultrasonic systems can also adopt this scheme. the

Background technique

At present, in the ultrasonic diagnostic system, the beamforming of the continuous wave Doppler receiving part has the following schemes: the scheme of quadrature demodulation and beamforming together, the scheme of digital beamforming, the scheme of multi-delay lines, and the scheme of single delay without compensation line plan, etc. the

Orthogonal demodulation combined with beamforming: add an orthogonal demodulator to each channel after the LNA. The delay link of beamforming is completed by controlling the phase of the local oscillator signal of the quadrature demodulator on each channel. The quadrature demodulation output I and Q signals are generally current signals, and the I and Q current signals of each channel can be directly connected together to complete the addition link of beamforming. Then add an I/V conversion (current to voltage) to complete quadrature demodulation and beamforming. In this solution, a local oscillator phase control quadrature demodulator is added to each channel, which makes the cost higher. Each quadrature demodulator needs to introduce local oscillator and phase control signals, which makes the control signal more complicated and the control more complicated. . Most of the control signals come from the digital domain, which is easy to introduce noise. the

Digital beamforming scheme: directly perform AD sampling on the RF signal on each channel after low-noise amplification, and complete the delay and addition links of beamforming in the digital domain. Due to the large dynamic range of the continuous wave signal, the RF sampling of the CW signal requires a high-speed AD with more bits (generally greater than 16 bits, and such a high-speed AD may not get a license). In addition, each channel needs to add an AD, so such a solution must be expensive. the

Multi-delay line scheme: add an analog delay line to each channel after the low-noise amplifier to complete the delay link of beamforming, and then use the operational amplifier as an adder to complete the accumulation link of beamforming. Although the multi-delay line scheme is beneficial to the impedance matching of each channel, adding a delay line to each channel makes the beamforming part quite large, which is not conducive to system integration. Of course, the cost has also increased. the

Single delay line solution without compensation: This solution is relatively close to the solution of the present invention, but the attenuation of each channel is not corrected by the compensation method. That is, the amplitude of each channel is not compensated, so there is a disadvantage of poor consistency of the amplitude of each channel. the

Contents of the invention

The technical problem to be solved by the present invention is to propose a compensated reverse application delay line to realize the beamforming scheme of the continuous wave signal in the ultrasonic diagnostic system in view of some shortcomings in the above-mentioned prior art. the

The present invention adopts following technical scheme: design the synthesis method of analog beam in a kind of continuous wave Doppler module, this method comprises the steps:

a. The multi-channel echo signal of the ultrasonic probe is amplified by low-noise amplification;

b. The amplified multi-channel echo signal performs amplitude compensation through the amplitude compensation element connected in series on the delay line, so as to compensate for the gain difference between the delay line LC network channels;

c. After amplitude compensation, the signals of each channel are added to the delay line LC network composed of inductors and capacitors from the taps corresponding to each channel;

d. The delay line LC network completes the signal accumulation while completing the signal delay of each channel signal, and finally outputs the beamforming signal from the signal output terminal of the LC network. the

In the case that the output of the low-noise amplification is a multi-channel voltage signal, the amplitude compensation element connected in series on the delay line is a resistor connected in series with the tap corresponding to each channel at the input end of the LC network, through Adjusting the resistance value of the resistor connected in series with the corresponding tap of each channel compensates the amplitude of the multiple voltage echo signals generated by the ultrasonic probe. the

The amplitude compensation element connected in series on the delay line can also be an operational amplifier connected in series with taps corresponding to each channel at the input end of the LC network, by adjusting the amplification of the operational amplifier connected in series to the corresponding taps of each channel multiples to compensate the amplitude of the multiple voltage echo signals generated by the ultrasonic probe. the

If the output of the low-noise amplifier is multiple current signals, I/V conversion should be performed on the current signals to obtain voltage signals. In this case, the amplitude compensation of the echo signal of each channel can be performed in the I/V conversion link, or the amplitude compensation of the voltage signal can be performed in the above-mentioned method after the I/V conversion. the

The technical solution adopted by the present invention to solve the technical problems also includes: designing a synthesis device for analog beams in a continuous wave Doppler module, comprising:

The delay line LC network composed of inductors and capacitors is used to receive the echo signals of each channel and complete the signal delay and signal accumulation of each channel signal, and finally output the analog beamforming signal;

The input signal amplitude compensation element serially connected to the input end of the delay line LC network is used to adjust the amplitude of the input signal of each channel entering the delay line LC network. The input signal amplitude compensation element can have the following implementation modes:

Embodiment 1: the input signal amplitude compensation element includes a resistor connected in series before each channel enters the input end of the LC network, the resistance value of the resistor connected in series in each channel is determined through experiments, and the resistance value of the resistor connected in series in each channel is determined through experiments. The selection principle of the resistance value of the resistor is required to compensate the difference in gain between the channels of the delay line LC network. the

Embodiment 2: the described input signal amplitude compensation element includes an operational amplifier connected in series before each channel enters the input end of the LC network, and the amplification factor of the operational amplifier connected in series in each channel is determined through experiments, and each channel The selection principle of the magnification of the operational amplifier connected in series is to compensate for the difference in gain between channels of the delay line LC network. the

The number of channels of the signal channel is large, for example, if the number of channels is N, then the LC network should have 2N taps, and the first to N channels are respectively connected in series with resistors R1 to RN to connect to the LC network. The 2nd to 2Nth even-numbered taps; the range of N is 8 to 64. the

When the number of channels of the signal channel is 10, the LC network has 20 taps, and the 1st to 10th channels are respectively connected in series with resistors R1 to R10 and connected to the 2nd to 20th even numbers of the LC network No. taps, the resistance values of series connected resistors R1 to R10 are: 510, 470, 363, 330, 270, 220, 151, 100, 51 and 33 ohms. the

Compared with the prior art, the method and device for analog beamforming in the continuous wave Doppler module of the present invention have the following advantages: since the analog delay line is only composed of an inductance-capacitance network, the price of the delay line itself is very low; In addition, the present invention reversely applies the analog delay line to simultaneously complete the delay and accumulation functions of beamforming, so that the continuous wave beamforming module only uses one delay line and does not need to add an operational amplifier to complete the accumulation function; the analog delay line is used to realize the CW Beamforming does not require any control, so the control of the entire CW module is simplified, and the coupling path of digital noise is reduced; due to the compensation method for the amplitude of each channel, the amplitude consistency of each channel of each CW echo is good. The above points determine that the device of the present invention is low in cost, small in size, and has good consistency in the CW echo amplitude of each channel. the

Description of drawings

Fig. 1 is the signal processing flowchart of continuous wave Doppler receiving module of the present invention;

Fig. 2 is a schematic diagram of ultrasonic probe focus echo;

Fig. 3 is the internal structural block diagram of the delay line LC network with N taps;

Fig. 4 is the functional block diagram that the reverse application analog delay line of the present invention realizes beamforming;

Figure 5 is a schematic block diagram of an LNA series resistance equivalent to an ideal voltage source plus the internal resistance of the voltage source;

Fig. 6 is an equivalent schematic block diagram corresponding to only the T20 tap having a signal input in Fig. 5;

Fig. 7 is the measurement model schematic diagram of technical effect of the present invention;

Figure 8 is a test waveform diagram of the signal added from the T2 tap to the analog delay line, wherein the thin solid line represents the waveform diagram of the amplifier output, and the thick solid line represents the waveform diagram of the signal before the input terminal is connected in series;

Figure 9 is a test waveform diagram of the signal added from the T4 tap to the analog delay line, wherein the thin solid line represents the waveform diagram of the amplifier output, and the thick solid line represents the waveform diagram of the signal before the input terminal is connected in series with the resistor;

Figure 10 is a test waveform diagram of signals added from T2 and T4 taps to the analog delay line, where the thin solid line represents the waveform diagram of the output of the amplifier, and the thick solid line represents the waveform diagram of the signal before the resistor is connected in series at the input end. the

Detailed ways

The device and method of the present invention will be described in further detail below in conjunction with the accompanying drawings and the embodiments shown in the accompanying drawings. the

The signal processing flow of the continuous wave (CW) Doppler receiving module proposed by the present invention is shown in FIG. 1 . The multi-channel echo signals of the probe are amplified by the low-noise amplifier, and the amplified signals enter the analog beamforming unit. The analog beam forming unit performs time-delay focus accumulation on the multi-channel amplified echo signals. After beamforming, multiple echo signals are synthesized into one signal. If the CW signal is transmitted using a square wave, a low-pass filter must be added after the analog beamforming to filter out the high-order harmonics of the square wave except the fundamental frequency to output a sine wave. The filtered signal enters the quadrature demodulation module. If the transmission is a sine wave, the output of the beam synthesis can be directly output to the quadrature demodulation module (low-pass or band-pass filters can also be added to suppress out-of-band noise). The quadrature demodulation module demodulates the input RF signal into I and Q baseband signals, which is the Doppler audio signal we really care about. The demodulated I and Q signals are respectively low-pass filtered to filter out the sum frequency components produced by quadrature demodulation. Low-pass filtering also has a function as an anti-aliasing filter before AD sampling. The signal after low-pass filtering needs to be adjusted in gain to fit the fluctuation range of AD input. After the gain adjustment, the I and Q two-way baseband signals are sampled by the ADC. The sampled data is processed by digital signal to output the spectrogram signal of CW Doppler and the stereo signal of the left and right channels. the

The focus of attention of the present invention is an analog beamforming unit based on a single delay line. Due to the different distances from the echo focus to each array element on the probe surface, the delays from the focus echo to each array element on the probe surface are different, as shown in Figure 2. The function of beamforming is to adjust the delay of each echo signal of the probe, compensate the delay difference from the focus echo signal to each probe array element, and add the echo signals of each channel in phase. The present invention adjusts the delay of each channel by using an analog delay line. The internal junction of the analog delay line is composed of LC network, and the internal structure principle block diagram of an N-tap delay line LC network is shown in Fig. 3 . The delay T _d for each tap is determined by:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\sqrt{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}$

Where: L _t is the total inductance of the delay line (unit: uH), C _t is the total capacitance of the delay line (unit: pF), and N is the total number of taps of the delay line. The total delay T _D is determined by the following formula:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}$

The characteristic impedance Z ₀ is determined by the following formula:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}$

The rise time t _r of the delay line is determined by the following formula:

${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; ro</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="ri"\; filenames="H06162698520061018E000031.png"\; state="\{\{state\}\}">ri</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Where: t _ro is the rising time of the output signal of the delay line, and t _ri is the rising time of the input signal of the delay line. The bandwidth BW of the delay line is determined by the following formula:

BW≈0.35/t _r

The total number of taps N of the delay line can be calculated by the following formula:

N≈(T _D /t _r ) ^1.36

Use the above parameters to select the appropriate delay line during design. the

Usually, the application of the delay line is to input the signal from IN, and output it from different taps _Tn to obtain different phase delay signals. In the ultrasound system, there are many CW echo signal channels (generally at least eight channels), and in order to achieve a certain delay accuracy, the volume of the delay line that can reach the target is relatively large. If a delay line is selected for each channel, the volume of the CW module will become large, which is not conducive to system integration, especially not conducive to the application of portable ultra-systems. The present invention adopts the method of reversely applying the delay line, and simultaneously completes the delay and accumulation functions of the CW signal beam synthesis process. And the amplitude compensation method is used to make the amplitude attenuation of each channel basically the same, which solves the problem that the amplitude of each channel is inconsistent due to the reverse application of the delay line. The technical solution of the present invention will be described below by taking the system with 10 CW echo signal channels as an example.

The CW echo signal of the ultrasonic system of the present invention is a 10-channel voltage signal after low-noise amplification. The parameters of the analog delay line used in the beamforming are: 20 taps, each tap has a delay of 20nS, the total delay is 400nS, and the characteristic impedance is 100OHM. The 10-channel voltage signal of the low-noise amplifier LNA9-0 is connected to the taps of the analog delay line: T20, T18, T16, T14, T12, T10, T8, T6, T4, and T2 through the series resistor R10-1. As shown in Figure 4. Where BF_OUT is an analog beamforming signal. During the test, the 10 voltage signals can be equivalent to 10 ideal voltage signal sources, and the resistors connected in series on the signals can be equivalent to the internal resistance of the voltage source, as shown in Figure 5. Since the internal resistance of an ideal voltage source is 0, if there is no signal in a certain channel, the corresponding tap is equivalent to grounding through a series resistance. Figure 6 shows an equivalent circuit where only the T20 tap has a signal input. the

It can be seen from the superposition principle of linear circuits that in Figure 5, the current flowing through the output resistance R11 to ground is equal to the algebraic sum of the currents generated when each tap is used as input alone. It is to apply the principle of superposition, and we complete the accumulation function of beamforming. According to the model in Figure 5, we can adjust the resistance value of the signal input series resistor (equivalent to the internal resistance of the voltage source in Figure 5) to compensate the amplitude of the signal generated by each channel at the IN terminal. Since the application of the delay line involves a network of inductors, capacitors, and resistors, and multiple excitations are added, it is difficult to quantitatively calculate the resistance value of the series resistor for compensation. We determined the resistance value of the compensation resistor through experiments. After testing, we selected the following combination of compensation resistors. the

                                       

Input tap number T2 T4 T6 T8 T10 T12 T14 T16 T18 T20 Series Resistance (Ohms) 510 470 363 330 270 220 151 100 51 33

After the test is compensated, the signal is input from each tap, and the amplitude measurement results obtained at the IN terminal are as follows:

                                                         

Input tap number T2 T4 T6 T8 T10 T12 T14 T16 T18 T20 output signal peak-to-peak 33.4 31.4 35.7 32.6 33 32.4 35.5 34.2 32.4 31.5 Output Voltage Relative to Input Signal Delay (ns) 40 82 124 160 202 236 269 318 360 430 Theoretical delay 40 80 120 160 200 240 280 320 360 400 Error with theoretical delay 0 2 4 0.3 2.4 4.3 11 2 0.46 30

Calculated according to the table data, the average value of the output signal is 33.21, and the standard deviation is 1.5mV. The gain difference between each channel does not exceed 1DB, which meets our requirements for gain consistency. There is a 30ns error at the input terminal of the delay T20, which is the result of the mismatch between the resistance of the T20 at the far end of the delay line and the impedance of the delay line which is only 30 OHM. If T20 is adjusted to 100OHM, in order to achieve the compensation effect, the series resistance of all input taps must be increased. This will inevitably increase the attenuation of the input signal. Therefore, the accuracy of the delay and the attenuation of the signal amplitude are the result of weighing the resistance of the series resistor. In addition, it is beneficial to us that the delay of the last tap is slightly larger, so the present invention adopts this group of series resistance resistance parameters. the

The following is a brief description of the working principle of the device of the present invention: the multi-channel voltage signal output by the low-noise amplifier is compensated for the signal amplitude through the resistance connected in series with the delay line, and the compensated signal is added to the LC network of the delay line from different taps, and enters the The signal after the LC network of the delay line is delayed by the LC network of the delay line. The delay of different tap input signals is determined by the number of LC units from the tap to the output IN terminal. Since the signals added by different taps all enter the LC network of the same delay line, according to the superposition principle, while the delay line completes the signal delay, it also completes the accumulation of the input signals of different taps, that is, the signal output by the delay line has been the delayed and accumulated beam-formed signal. the

In order to test the technical effect of the method and device of the present invention, the present invention specially designed a measurement model as shown in FIG. 7 . After the amplitude attenuation is compensated by using the input series resistance, the delay accumulation test is carried out by simulating the delay line. Since the output amplitude of the analog delay line is small, in order to obtain more accurate test results, the output of the analog delay line is amplified for testing. the

In the schematic diagrams of the three test results shown in Figure 8, Figure 9 and Figure 10, the thin solid line represents the waveform diagram of the output of the amplifier, and the thick solid line represents the waveform diagram of the signal before the resistor is connected in series at the input end. The thick solid line CH1 (CH1 and CH2 in the figure are channel 1 and channel 2 of the oscilloscope) is the waveform at INPUT. Since the output waveform at BF_OUT is small, we use an amplifier to amplify it. The delay generated by the amplifier It is 285.4ns, and the thin solid line represents the output AMP_OUT of the CH2 waveform amplifier. the

The desired delay result of the present invention is the delay from BF_OUT to INPUT, and the measured values in FIG. 8 to FIG. 10 are the time difference from the peak of the AMP_OUT signal to the peak of the INPUT signal. The frequency of the signal is 2.5MHz and the period is 400ns. Therefore, the time difference between the peak of the INPUT signal and the next peak of AMPOUT is: 400ns minus the time difference between the peak of the AMP_OUT signal and the peak of the INPUT signal, this is the delay of AMP_OUT relative to INPUT, and then subtracting the delay of the amplifier 285.4ns, it is BF_OUT Delay relative to INPUT. The measurement accuracy of this delay may be affected by the accuracy of the delay measurement of the amplifier itself. If you want to measure the delay difference input by two taps, you can directly calculate the difference between the AMP_OUT measured by the two taps and the INPUT delay, which excludes the delay measurement results of the amplifier from the two taps. The impact of delay time difference measurement results. the

Through the above tests, it can be proved that the compensated reverse application analog delay line fully meets the requirements of the analog beamforming of the CW module of the ultrasonic diagnostic system. Therefore, a new method is provided for the realization of the CW receiving module in the ultrasonic diagnosis system. the

The most important key point of the present invention is to use the series resistance of each input tap of the analog delay line to perform amplitude compensation. This compensation is not limited to this resistance, the entire The amplitude can be compensated on the path. For example, on this path, each channel is serially connected to an operational amplifier, and each channel adjusts different amplification factors for amplitude compensation. If the output of the low-noise amplifier is a current signal, the application of this solution can first perform I/V conversion on the current signal, and the conversion link can also perform amplitude compensation for each channel. the

Claims (5)

1. the synthetic method of analog beam in the continuous wave Doppler module, it is characterized in that: this method comprises the steps:

A. the multi-path echo signal of ultrasound probe is exaggerated by the low noise amplification;

B. described multi-path echo signal through amplifying carries out the amplitude compensation by the amplitude compensating element that is serially connected on the delay line, the gain inequality when synthesizing with the compensation wave beam between delay line LC network channel;

C. each channel signal after the amplitude compensation joins the delay line LC network of being made up of inductance and electric capacity from the tap of each passage correspondence;

D. when finishing the signal lag of each channel signal, finish signal by described delay line LC network and add up, last signal output part beamformer output composite signal by described LC network.

2. the synthetic method of analog beam in the continuous wave Doppler module according to claim 1, it is characterized in that: described low noise is amplified output plurality of voltages signal, the described amplitude compensating element that is serially connected on the delay line is the resistance of the tap serial connection corresponding with each passage of the input at described LC network, and the resistance value that is serially connected in the resistance of the corresponding tap of each passage by adjusting compensates the amplitude of the plurality of voltages echo-signal that described ultrasound probe produces.

3. the synthetic method of analog beam in the continuous wave Doppler module according to claim 1, it is characterized in that: described low noise is amplified output plurality of voltages signal, the described amplitude compensating element that is serially connected on the delay line is the operational amplifier of the tap serial connection corresponding with each passage of the input at described LC network, and the amplification that is serially connected in the operational amplifier of the corresponding tap of each passage by adjusting compensates the amplitude of the plurality of voltages echo-signal that described ultrasound probe produces.

4. the synthetic method of analog beam in the continuous wave Doppler module according to claim 1 is characterized in that: if described low noise is amplified what exported is the multichannel current signal, then earlier described current signal is carried out the I/V conversion.

5. the synthetic method of analog beam in the continuous wave Doppler module according to claim 4 is characterized in that: the amplitude compensation of each passage echo-signal is carried out in the I/V conversion links, or in I/V conversion back voltage signal is carried out the amplitude compensation.

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