CN109186693B - Self-adaptive ultrasonic echo signal detection circuit - Google Patents
Self-adaptive ultrasonic echo signal detection circuit Download PDFInfo
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- CN109186693B CN109186693B CN201810871160.1A CN201810871160A CN109186693B CN 109186693 B CN109186693 B CN 109186693B CN 201810871160 A CN201810871160 A CN 201810871160A CN 109186693 B CN109186693 B CN 109186693B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
- G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
Abstract
The invention discloses an echo signal detection circuit of self-adaptive ultrasonic waves, wherein an echo signal butted by a front channel circuit is amplified and filtered, and a main channel circuit is used for carrying out re-amplification processing and zero-crossing comparison to generate a main channel signal containing interference pulses; the auxiliary channel circuit pre-receives signals, carries out peak detection and attenuates according to a certain proportion to obtain a comparison level, the formal received signals and the comparison level are triggered and compared to generate a first pulse train signal, a gating signal and a main channel signal are generated according to the falling edge of the first pulse to carry out AND operation, and a second pulse train signal is output to trigger the timing module to stop timing to obtain a time difference. The invention adopts a peak detection circuit and cooperates with a working mode of continuously receiving and sending signals twice, dynamically tracks the pre-received signals and flexibly adjusts the comparison level, thereby solving the problem of pulse train wave hopping; in addition, the influence of the noise pulse of the main channel on time measurement is avoided by the aid of the gating signal, and the problem that the phase of a pulse train is advanced or lagged in a quarter period is solved by the aid of the zero-crossing comparator of the main channel.
Description
Technical Field
The invention belongs to the technical field of ultrasonic gas flow measurement, and particularly relates to an echo signal detection circuit of self-adaptive ultrasonic waves.
Background
In recent years, the ultrasonic gas flow measurement technology has been rapidly developed, which has led to the rapid development of the ultrasonic gas flow meter industry. Compared with the traditional flowmeter, the ultrasonic gas flowmeter has the advantages of wide measurement range, high precision, strong stability and the like, and is very suitable for industrial and civil gas measurement.
The accuracy of the instantaneous flow of the ultrasonic gas flowmeter based on the time difference method mainly depends on the accuracy of the time for measuring the echo signal. In the ultrasonic gas flow measurement, along with the continuous enhancement of the gas flow velocity, the non-uniform flow field of the pipeline and other factors, the received echo signal can be attenuated to different degrees. The circuit system is a key technology of the ultrasonic flowmeter for accurately detecting the nth wave echo signal under different air flows so as to measure the echo time.
The ultrasonic transceiver is usually designed by using the principle of forward and reverse piezoelectric effect. The operating system is a resonant system, so that under the action of the external excitation signal, the received waveform appears as a resonant waveform of the impulse oscillation, as shown in fig. 1. As can be seen from fig. 1, the common oscillation frequency is the inherent operating frequency of the ultrasonic sensor, and the oscillation amplitude of the common oscillation frequency gradually increases and gradually decreases when the amplitude reaches the maximum value.
The accurate measurement of the arrival time of the received echo signal usually requires that the amplitude-modulated oscillating wave received by the sensor is converted into a rectangular pulse wave signal by a comparator. If each sine wave in the received echo signal participates in the comparison trigger, the received echo signal after passing through the comparator is a rectangular pulse train, as shown in fig. 2. In this case, if the time at which the first received echo of the ultrasonic receiving end arrives is assumed to be the echo time Δ T, the transit time of the second received echo is Δ T + T0And the transmission time of the third received echo is delta T +2T0…, the kth received echo time is Δ T + (k-1) T0. Where k is a positive integer, and T0 is the period of the received echo signal, the natural oscillation period of the ultrasonic sensor.
In order to accurately measure the transit time of the received echo signal, it is important to set the comparison level of the received wave to determine the parameter point at which the arrival time is obtained from the several echoes. When the comparison level is fixed and unchanged, the amplitude of the received echo changes, which causes two problems: firstly, the phenomenon of wave hopping caused by the change of signal amplitude is shown in fig. 3(a), (b) and (c); secondly, even if the wave-hopping phenomenon does not occur, the steep degree of the amplitude rising change leads or lags by Δ t', as shown in fig. 4.
As can be seen from fig. 3, when the amplitude of the received echo signal changes greatly, the phenomenon of pulse skipping of the pulse train occursSuch as a mouse. At this time, the comparison level falls on the first or third received wave from the original second received wave. The severe consequence of the hopping phenomenon is that gross errors occur in the detected transmission time. The coarse error value is the period T0Is an integer multiple of that which is a condition that high precision ultrasonic gas flow meters are not allowed to take place.
When the amplitude of the received echo signal changes slightly, although the output pulse train does not generate a serious wave-hopping phenomenon, the amplitude of the received echo signal still causes a small amplitude change of the sine wave slope, which causes a little phase advance or delay of the pulse train in an interval (a quarter period) in which the sine wave amplitude increases, and directly causes an echo detection time error Δ t'. When the amplitude of the received echo signal increases, the pulse train leads by Δ t', as shown in fig. 4 (a); when the amplitude of the received echo signal decreases, a burst lag Δ t' occurs, as shown in fig. 4 (b). The time Δ t' for the echo detection time to advance or lag is much less than the effect of the beat wave, but this problem cannot be ignored in the high-precision time measurement.
In summary, in the conventional ultrasonic gas flow measurement technology, there are problems of burst skipping and phase advance or phase delay of the burst within a quarter period.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a self-adaptive ultrasonic echo signal detection circuit, which solves the problems of pulse train wave hopping and phase advance or delay of pulse trains in a quarter period by adopting a method of processing received echo signals by an auxiliary channel circuit and a main channel circuit.
In order to achieve the above object, an echo signal detection circuit of an adaptive ultrasonic wave according to the present invention includes:
the pre-channel circuit is used for amplifying and filtering the received echo signals excited twice in a measurement period to obtain pre-channel signals and outputting the pre-channel signals to the main channel circuit and the auxiliary channel circuit;
the echo signals excited twice are respectively a pre-receiving signal and a formal receiving signal;
the main channel circuit comprises an amplifier and a zero-crossing comparator, wherein the amplifier performs re-amplification processing on a received signal (a preposed channel signal) output by the preposed channel circuit and then transmits the amplified signal to the zero-crossing comparator for comparison to generate a main channel signal containing interference pulses;
an auxiliary channel circuit, including peak detection circuit, attenuation circuit, comparator and one-shot trigger; the peak detection circuit performs peak detection on the pre-received signal output by the front channel circuit to obtain a peak detection signal, outputs the peak detection signal to the attenuation circuit, attenuates the peak detection signal according to a certain proportion to obtain a comparison level, and the comparison level is fixed on the nth received echo signal which is determined according to the specific implementation situation;
the comparator triggers and compares a formal receiving signal output by the front channel circuit with a comparison level to generate a first pulse train signal; the falling edge of the first pulse train signal triggers the monostable trigger to generate level inversion to generate a gating signal, the gating signal and the main channel signal output a second pulse train signal through AND operation, and the second pulse train signal stops timing of the triggering timing module, so that the time between the emission signal and the n +1 th received echo in the received echo signals is measured.
The purpose of the invention is realized as follows:
the invention relates to an echo signal detection circuit of self-adaptive ultrasonic waves, which comprises a preposed channel circuit, a main channel circuit and an auxiliary channel circuit, wherein the preposed channel circuit amplifies and filters received echo signals excited twice in a measurement period to obtain a preposed channel signal and outputs the preposed channel signal to the main channel circuit and the auxiliary channel circuit; the main channel circuit performs re-amplification processing on the preposed channel signal and then transmits the pre-amplified channel signal to the zero-crossing comparator for comparison to generate a main channel signal containing interference pulses; the auxiliary channel circuit comprises a peak detection circuit, an attenuation circuit, a comparator and a one-shot trigger, wherein the peak detection circuit performs peak detection on a pre-received signal output by the front channel circuit to obtain a peak detection signal, the peak detection signal is output to the attenuation circuit, the peak detection signal is attenuated according to a certain proportion to obtain a comparison level, the comparison level is fixed on the nth received echo signal, and the nth received echo signal is determined according to a specific implementation condition; the comparator triggers and compares a formal receiving signal output by the front channel circuit with a comparison level to generate a first pulse train signal; the falling edge of the first pulse train signal triggers the monostable trigger to generate level inversion to generate a gating signal, the gating signal and the main channel signal output a second pulse train signal through AND operation, and the second pulse train signal stops timing of the triggering timing module, so that the time between the emission signal and the n +1 th received wave in the received echo signal is measured. The auxiliary channel dynamically tracks the pre-received signal and flexibly adjusts the comparison level by adopting a peak detection circuit and matching with a working mode of continuously receiving and sending signals twice, thereby accurately detecting the echo signal and solving the problem of pulse train wave hopping; in addition, the gating signal generated by the auxiliary channel provides a gating effect for a plurality of pulses of the main channel, so that the influence of noise pulses of the main channel on time measurement is avoided; the main channel adopts a zero-crossing comparator, so that the problem that the pulse train generates phase lead or lag in a quarter period is solved.
Drawings
FIG. 1 is a schematic diagram of a received echo signal waveform of an ultrasonic sensor;
FIG. 2 is a schematic diagram of a pulse train after shaping of a received echo signal;
FIG. 3 is a graph illustrating the effect of varying received echo amplitude on the resulting pulse train when compared to a level constant, wherein (a) is the pulse train when the received echo amplitude is not at the second wave energy trigger, (b) is the pulse train when the received echo amplitude is reduced to a third wave trigger, and (c) is the pulse train when the received echo amplitude is increased to the first wave trigger;
FIG. 4 is a schematic diagram of a burst when the amplitude of the received wave changes but no jump occurs, (a) a burst with a lead Δ t at the trigger time after the amplitude of the received echo increases, and (b) a burst that leads △ t at the trigger time after the amplitude of the received echo decreases;
FIG. 5 is an overall block diagram of the echo signal detection circuit of the present invention;
FIG. 6 is a schematic diagram of a pulse train when the comparison level is dynamically changed according to the present invention;
FIG. 7 is a schematic diagram of the dynamically changing comparison level based on peak detection according to the present invention;
FIG. 8 is a schematic diagram of the output pulse train of the zero-crossing comparator of the present invention;
FIG. 9 is a schematic diagram of the effect of the main channel interference signal on the burst according to the present invention;
FIG. 10 is a functional schematic of the strobe signal of the present invention;
fig. 11 is a schematic diagram of an actually measured waveform of an echo signal detection circuit according to the present invention, where (a) is a waveform diagram of an input/output signal of a front channel, (b) is a timing waveform diagram of an output signal of the front channel and a strobe signal, (c) is a timing waveform diagram of a pre-received signal, a main received signal, and a maximum peak signal stored in a peak detection circuit, and (d) is a timing waveform diagram of a final output square wave signal and a secondary amplified received signal of a main channel.
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.
In order to solve the problems that when the amplitude of a received wave changes, a pulse train generates wave hopping and a little lead or lag occurs in the rising edge of a quarter cycle of a signal, the invention adopts a method for processing the received echo signal by double channels.
In this embodiment, as shown in fig. 5, the present invention provides an echo signal detection circuit of adaptive ultrasound, including a front channel circuit, a main channel circuit, and an auxiliary channel circuit:
the front channel circuit is used for amplifying and filtering the received echo signals excited twice in a measuring period to obtain front channel signals and outputting the front channel signals to the main channel circuit and the auxiliary channel circuit. The echo signals of the two times of excitation are respectively a pre-receiving signal and a formal receiving signal.
In the present embodiment, as shown in fig. 5, the front channel circuit of the present invention includes a first-order high-pass circuit composed of an in-phase amplifier U1 and R3, C1; the reverse input end of the non-inverting amplifier U1 is connected with one end of the resistor R1 and one end of the resistor R2; the other end of the resistor R1 is grounded; the other end of the resistor R2 is connected with the output end of the homonymous amplifier U1; the output end of the equidirectional amplifier U1 is connected with one end of a capacitor C1 of the first-order high-pass circuit, one end of a resistor R3 is connected with the other end of the capacitor C1, and the other end of the resistor R3 is grounded. So that the phase of the received echo signal is substantially synchronized with the phase of the amplified (in-phase amplifier output) echo signal. The equidirectional amplified signal output by the equidirectional amplifier U1 is input to a first-order high-pass circuit and is used for suppressing a direct-current noise component and a low-frequency noise signal in the equidirectional amplified signal to obtain a pre-channel signal and output the pre-channel signal to a main channel circuit and an auxiliary channel circuit.
The main channel circuit comprises an amplifier U2 and a zero-crossing comparator U3; the pre-channel circuit is configured to amplify a received signal (pre-channel signal) output by the pre-channel circuit, and then transmit the amplified signal to the zero-crossing comparator U3 for comparison, so as to generate a main channel signal S0 including interference pulses. The positive input end of the amplifier U2 is connected at the connection point of the resistor R3 and the capacitor C1 of the pre-channel circuit; a resistor R4 is connected between the inverting input of the amplifier U2 and ground, while a resistor R5 is connected between the inverting input and the output of the amplifier U2.
The main channel circuit further comprises a first-order high-pass circuit composed of R6 and C2, the first-order high-pass circuit is connected between the amplifier U2 and the zero-crossing comparator U3 and is used for filtering signals amplified by the amplifier U2. One end of a capacitor C2 of the first-order high-pass circuit is connected with the output end of an amplifier U2, and one end of a resistor R6 is connected with the other end of the capacitor C2; the other end of the resistor R6 is grounded; the junction of the resistor R6 and the capacitor C2 is connected to the positive input terminal of the zero-crossing comparator U3, and the negative input terminal of the zero-crossing comparator U3 is grounded.
And the auxiliary channel circuit is used for adopting a peak detection circuit and matching with the working mode of continuously transmitting and receiving signals twice, the control switch K2 is connected to the pre-amplified output end when receiving a pre-received signal, and the control switch K2 is connected to the ground when receiving a main signal. The auxiliary channel circuit comprises a peak detection circuit, an attenuation circuit consisting of resistors R9 and R10, a comparator U7 and a one-shot trigger U8; the peak detection circuit stores a single peak value of the pre-received signal output by the front channel circuit, outputs a peak detection signal S4, and performs certain proportion attenuation through attenuation resistors R9 and R10 of the attenuation circuit to ensure that the comparison level of a comparator U7 is fixed on the nth received wave; the comparator U7 triggers and compares the formal receiving signal output by the front channel circuit with the comparison level to generate a first pulse train signal S1; the falling edge of the first pulse train signal S1 triggers the one-shot trigger U8 to generate level inversion, a gating signal S2 is generated, the gating signal S2 and a main channel signal S0 pass through and operation, and a second pulse train S3 is output; the second burst S3 will trigger the timing module to stop timing, thereby measuring the time between the n +1 th received echo in the transmitted signal and the received echo signal. When the pre-receiving signal is received and processed, the one-shot outputs the strobe signal S2 low under the control of the reset signal, masking the output of the second output burst S3.
The peak detection circuit comprises a first operational amplifier U5 and a second operational amplifier U6 which are cascaded; the positive input end of the first operational amplifier U5 is grounded, and the negative input end of the first operational amplifier U5, the positive input end of the comparator U7 and the negative input end of the second operational amplifier U6 are connected to the connection point of the resistor R3 and the capacitor C1 of the pre-channel circuit; a resistor R7 is further connected to the inverting input end of the second operational amplifier U6, and the inverting input end and the output end of the second operational amplifier U6 are connected; a diode D1 is connected between the reverse input end and the output end of the first operational amplifier U5, a diode D2 is connected between the output end of the first operational amplifier U5 and the forward input end of the second operational amplifier U6, and a parallel circuit consisting of a detection resistor R8 and a detection capacitor C2 is connected between the forward input end of the second operational amplifier U6 and the ground; a switch K1 is also connected on the parallel circuit, and the switch K1 is in a grounding state in a default state; when the pre-receiving signal is coming, the MCU prompts the switch K1 to be switched to a suspension state through an effective control signal; at this time, the detection capacitor C2 starts to charge, and its essence is to track and store the amplitude of the pre-received signal; when the pre-receiving signal arrives, the peak value detection circuit stores the single peak value of the pre-receiving signal and stores the single peak value until the formal receiving signal is compared with the comparator U7, and the stored peak value is released through the state transition of the switch K1.
The following is an analysis of how the echo signal detection circuit of the present invention can solve the problems of pulse train jumping and a little lead or lag occurring in the rising edge of one quarter of the signal cycle.
In order to solve the problem of pulse train jumping, a method is adopted in which the comparison level of the comparator U7 is dynamically changed according to the amplitude change of the received echo signal, and the comparison level is always maintained at the nth (for example, n is 2) wave, as shown in fig. 6.
In fig. 6, assuming that the amplitude of the received echo signal increases, if the comparison level remains unchanged, a wave-skipping phenomenon obviously occurs. However, if the comparison level is increased along with the increase of the amplitude of the received echo signal, the trigger on the nth wave is still maintained, so that the phenomenon of wave skipping can be avoided. When the amplitude of the received echo signal is reduced, the comparison is also reduced, and the non-bouncing wave can be maintained.
By observing the amplitude values of a large number of received echo signals, it is found that the amplitude value of each received echo signal and the ratio of the peak value of the received echo signal have a certain ratio relation. Table 1 lists the ratio of the amplitude to the peak value of the different received echo signal waves, and it can be seen from the table that the ratio of the amplitude of the nth wave received echo signal to the maximum peak value of the received echo signal is about n/6, where n is an integer of 1,2,3,4,5, 6. Therefore, if the comparison level is fixed to the nth wave signal, the attenuation ratio of the maximum single peak can be set to a certain value in the interval ((n-1)/6, n/6), and the corresponding comparison level range is determined accordingly.
TABLE 1
| Test | Wave | 1 | |
|
Wave 4 | Wave 5 | Wave 6 |
| |
0.17 | 0.34 | 0.54 | 0.74 | 0.89 | 1.00 | |
| |
0.17 | 0.33 | 0.53 | 0.69 | 0.86 | 0.97 | |
| |
0.17 | 0.33 | 0.53 | 0.72 | 0.89 | 0.97 | |
| Group 4 | 0.17 | 0.33 | 0.53 | 0.69 | 0.86 | 0.97 | |
| Group 5 | 0.17 | 0.34 | 0.54 | 0.74 | 0.89 | 1.00 |
Therefore, the invention provides a method for dynamically tracking the peak value of the received echo signal based on peak detection. After the peak detection circuit detects the maximum peak value of the received echo signal each time, attenuation resistors R9 and R10 of the attenuation circuit are attenuated in a certain proportion according to the ratio in Table 1 to obtain a comparison level, so that when the amplitude of the received echo signal changes, the comparison level also changes correspondingly and is fixed on the rising edge of the nth received wave.
However, the peak detection circuit needs to track and detect the echo signal received this time each time, and when the maximum peak value of the received echo signal is to be detected, the comparator has missed the rising edge part of the echo signal received this time, and cannot utilize the comparison level obtained this time. In order to solve the problem, the invention stores the single peak value of the echo signal received this time, and when the echo signal received next time arrives, the comparator takes out the stored comparison level value for comparison. In this process, since the time interval of the echo signals received twice can be set to be very small, the single peaks of the echo signals received twice can be considered to be the same. As shown in fig. 7, the transmission circuit continuously transmits two ultrasonic signals each time measurement (one measurement cycle): firstly, pre-transmitting an ultrasonic signal to obtain a pre-receiving signal; the comparator stores the peak value of the pre-received signal; after a short time, transmitting a formal transmitting signal once again and obtaining a formal receiving signal; the comparator compares the formal received signal with the stored comparison level; when the amplitude of the ultrasonic signal is increased (or decreased), the comparison level is automatically increased (or decreased), so that the problem of wave jumping of the pulse train is avoided.
In order to ensure that the received pulse train does not lead or lag in phase within a quarter of a cycle as the amplitude of the received echo signal fluctuates, the invention introduces the received echo signal into a main channel containing a zero-crossing comparator. As shown in fig. 8, if there is a change in the signal amplitude with respect to the same received signal, the pulse train output by the zero-crossing comparator does not change at the zero-crossing time.
However, the zero-crossing comparison method adopted on the main channel also brings another serious problem: not only the received echo signal but also a series of noise signals may be superimposed on the main channel, so that the noise signals also participate in the zero-crossing level comparison before the received echo signal arrives, and an interference pulse train is formed. The interference pulse train is superimposed on the pulse train generated by the received echo signal, which not only makes the interference signal as a valid pulse to cause misjudgment, but also makes the pulse output by the circuit shaping very messy, as shown in fig. 9.
In order to solve the influence of interference pulses on echo measurement, a gating pulse width signal is added to the auxiliary channel. The strobe signal is generated by the pulse train S1 of the n-th wave received wave triggering the one-shot flip-flop by a falling edge, as shown in fig. 10. Therefore, the generated gating pulse width signal and the pulse train signal with the complex main channel can gate and select the useful pulse train S3 generated by the n +1 wave receiving wave, thereby shielding the influence of the interference pulse train in the main channel on time measurement and ensuring that the pulse wave generated by the n +1 wave signal is positioned at the forefront position of the pulse train.
In fig. 10, the falling edge of the one shot flip-flop is used for triggering to ensure that the first pulse anded with strobe signal S2 is a complete periodic pulse. Note that, if the waveform of the n +1 th reception wave-shaped output is taken as the first pulse wave in the signal S3. The comparison level of the auxiliary channel should be fixed at the nth received wave.
Fig. 11 is a schematic diagram of a measured waveform in the process of processing a received echo signal by using the echo signal detection circuit of the present invention.
In summary, the auxiliary channel adopts the peak detection circuit and cooperates with the working mode of continuously receiving and transmitting signals twice, so as to solve the problem of pulse train wave hopping; in addition, the gating signal generated by the auxiliary channel provides a gating effect for a plurality of pulses of the main channel, so that the influence of noise pulses of the main channel on time measurement is avoided; the main channel adopts a zero-crossing comparator, so that the problem that the pulse train generates phase lead or lag in a quarter period is solved.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (4)
1. An echo signal detection circuit for adaptive ultrasound, comprising:
the preposed channel circuit is used for amplifying and filtering the received echo signals excited twice in one measuring period and outputting the amplified and filtered echo signals to the main channel circuit and the auxiliary channel circuit;
the echo signals excited twice are respectively a pre-receiving signal and a formal receiving signal;
the main channel circuit comprises an amplifier and a zero-crossing comparator, wherein the amplifier performs re-amplification processing on a received signal output by the pre-channel circuit, namely the pre-channel signal, and then transmits the amplified signal to the zero-crossing comparator for comparison to generate a main channel signal containing interference pulses;
an auxiliary channel circuit, including peak detection circuit, attenuation circuit, comparator and one-shot trigger; the peak detection circuit performs peak detection on the pre-received signal output by the front channel circuit to obtain a peak detection signal, outputs the peak detection signal to the attenuation circuit, attenuates the peak detection signal according to a certain proportion to obtain a comparison level, and the comparison level is fixed on the nth received echo signal which is determined according to the specific implementation situation;
the comparator triggers and compares a formal receiving signal output by the front channel circuit with a comparison level to generate a first pulse train signal; the falling edge of the first pulse train signal triggers the monostable trigger to generate level inversion to generate a gating signal, the gating signal and the main channel signal output a second pulse train signal through AND operation, and the second pulse train signal stops timing of the triggering timing module, so that the time between the emission signal and the n +1 th received echo in the received echo signals is measured.
2. The adaptive ultrasonic echo signal detection circuit according to claim 1, wherein the pre-channel circuit includes an in-phase amplifier and a first-order high-pass circuit;
the forward input end of the non-inverting amplifier is used for receiving echo signals excited twice, and the output of the non-inverting amplifier is connected to the first-order high-pass circuit and used for suppressing direct-current noise components and low-frequency noise signals in the echo signals amplified in the non-inverting amplifier to obtain a front channel signal and outputting the front channel signal to the main channel circuit and the auxiliary channel circuit.
3. The adaptive ultrasonic echo signal detection circuit of claim 1, wherein the main channel circuit further comprises a first order high pass circuit connected between the amplifier and the zero-crossing comparator for filtering the echo signal amplified by the amplifier.
4. The adaptive ultrasonic echo signal detection circuit according to claim 1, wherein the peak detection circuit comprises a first operational amplifier and a second operational amplifier which are cascaded, and a parallel circuit comprising a detection resistor and a detection capacitor connected between a forward input terminal of the second operational amplifier and ground; the parallel circuit is also connected with a switch in parallel, and the switch is in a grounding state in a default state; when the pre-receiving signal is coming, the MCU prompts the switch to be switched to a suspension state through an effective control signal; at the moment, the detection capacitor starts to be charged, namely, the amplitude of the pre-received signal amplified by the first operational amplifier is tracked and stored; when the pre-receiving signal arrives, a detection capacitor of the peak detection circuit stores a single-peak signal of the pre-receiving signal, and stores the single-peak signal until the comparison between the formal receiving signal and the comparator is finished, and then restores to a default state again through state transition of a switch, and releases the stored single-peak signal; the single-peak signal is amplified by the second operational amplifier and then is output to the attenuator as a peak detection signal output by the peak detection circuit.
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