A piezoelectric MEMS ultrasonic sensor ranging circuit and method

Abstract

The application belongs to the field of piezoelectric MEMS sensors, and relates to a piezoelectric MEMS ultrasonic sensor ranging circuit and a ranging method, which comprise an MCU, a high-voltage pulse driving circuit, an adaptive impedance matching network, a piezoelectric MEMS ultrasonic transducer, an active damping network, a preamplifier, a band-pass filter and a time gain controller; the high-voltage pulse driving circuit can greatly improve the emission sound pressure of the transducer and improve the measurement range; a controllable switch is designed at one end of the damping resistor, which can improve the emission efficiency and reduce the residual vibration, thereby reducing the measurement blind area; the adaptive impedance matching network is introduced, which can adjust the impedance inconsistent between different devices due to temperature and aging degree to the impedance matched with the ranging circuit, effectively improve the sensitivity and emission efficiency of the device, and the high sensitivity can improve the distance measurement precision of the ranging circuit.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric MEMS sensors and relates to a piezoelectric MEMS ultrasonic sensor ranging circuit and ranging method. Background Technology

[0002] Piezoelectric MEMS transducers utilize piezoelectric thin films, such as lead zirconate titanate (PZT) or aluminum nitride (AlN) films, which vibrate mechanically under an electric field. This process, known as the inverse piezoelectric effect, causes the transducer to emit ultrasonic waves. When receiving the sound waves, the vibration of the piezoelectric film generates charges at the electrode terminals; this process, known as the direct piezoelectric effect, receives the ultrasonic echo. Piezoelectric MEMS transducers can be applied in fields such as medical imaging, consumer electronics, and automotive electronics. Regardless of whether the application is in distance sensing, fingerprint imaging, or medical imaging, the core principle is to measure the time of flight and echo amplitude between the emitted and received echoes. Different imaging algorithms are used depending on the specific application requirements to measure the distance between the sensor and the object being measured or to image the measured area.

[0003] The existing piezoelectric MEMS ultrasonic sensor ranging circuit consists of a transmitting circuit, a piezoelectric MEMS transducer, a receiving circuit, and a controller. Its operation involves the transmitting circuit emitting a specified number of pulses to the piezoelectric MEMS transducer to generate ultrasonic waves. After propagation, the ultrasonic waves are reflected by the object being measured. The piezoelectric MEMS transducer converts the reflected ultrasonic waves into an electrical signal. The receiving circuit amplifies and filters the echo signal, and the controller calculates the flight time between the transmitted and received echoes. Combined with the speed of sound in the propagation medium, the distance between the piezoelectric MEMS transducer and the object being measured can be calculated. The existing ranging circuit has the following problems:

[0004] 1. Measurement blind zone and measurement distance are mutually exclusive; a small measurement blind zone usually corresponds to a small measurement distance, while a large measurement distance often results in a large measurement blind zone.

[0005] 2. Insufficient suppression of ringing effect. After the transmission, the piezoelectric MEMS transducer has residual oscillation, which cannot be eliminated quickly. This results in a large absolute value of the blind zone even for sensors with small measurement blind zones. The residual oscillation time after the transmission ends is >1ms (200kHz PMUT), and the minimum detection distance is limited to >10cm.

[0006] 3. Lack of dynamic impedance matching: The fixed LC matching network only adapts to the nominal impedance. When the ambient temperature changes by 20°C, the impedance shifts by ±15%, resulting in a decrease in energy transmission efficiency of more than 40%.

[0007] In summary, piezoelectric MEMS ultrasonic systems suffer from residual vibration interference, short measurement distance, and low transmission efficiency during short-distance measurements. Summary of the Invention

[0008] To address the aforementioned problems in the prior art, the present invention employs a piezoelectric MEMS ultrasonic sensor ranging circuit, comprising: an MCU, a high-voltage pulse drive circuit, an adaptive impedance matching network, a piezoelectric MEMS ultrasonic transducer, an active damping network, a preamplifier, a bandpass filter, and a time gain controller.

[0009] The MCU is connected to the high-voltage pulse drive circuit, the active damping network, and the adaptive impedance matching network, respectively. The active damping network is connected in parallel with the piezoelectric MEMS ultrasonic transducer. The output of the high-voltage pulse drive circuit is connected to the input of the adaptive impedance matching network and the input of the preamplifier. The output of the adaptive impedance matching network is connected to the input of the piezoelectric MEMS ultrasonic transducer. The output of the piezoelectric MEMS ultrasonic transducer is connected to the input of the preamplifier. The output of the preamplifier is connected to the input of the bandpass filter. The output of the bandpass filter is connected to the input of the time gain controller. The output of the time gain controller is connected to the MCU.

[0010] On the other hand, the present invention employs a ranging method based on the above-mentioned piezoelectric MEMS ultrasonic sensor ranging circuit, comprising:

[0011] S1. Set the capacitance of the adaptive impedance matching network according to the ranging circuit of the piezoelectric MEMS ultrasonic sensor;

[0012] S2. The pulse transmitter controller transmits N transmission pulses, while the damping controller disconnects the active damping switch of the active damping network by sending a low level signal.

[0013] S3. After the N transmission pulses are transmitted, the damping controller sends a high level to close the active damping switch of the active damping network. The pulse transmission controller then sends N / 5 active damping pulses after a half-cycle delay. After the active damping pulses are transmitted, the damping controller sends a low level after a one-cycle delay to open the active damping switch of the active damping network.

[0014] S4. The transmitted pulse and the active damped pulse are transmitted to the piezoelectric MEMS ultrasonic transducer through the high-voltage pulse drive circuit and the adaptive impedance matching network. The piezoelectric MEMS ultrasonic transducer generates ultrasonic waves. The ultrasonic waves propagate through the air to the metal plate under test and are reflected back. The piezoelectric MEMS ultrasonic transducer receives the reflected echo and converts the echo into an electrical signal, i.e., the ultrasonic echo signal.

[0015] S5. The ultrasonic echo signal is transmitted to the ADC for digitization via a preamplifier, bandpass filter and time gain controller. The ranging module calculates the distance based on the digitized ultrasonic echo signal.

[0016] The beneficial effects of this invention are:

[0017] 1. The high-voltage pulse drive circuit of this invention can boost low-voltage pulses to tens or even hundreds of V, significantly increasing the transducer's emitted sound pressure, thereby increasing the echo amplitude, enhancing the signal-to-noise ratio, and thus improving the measurement range. 2. This invention designs a controllable active damping switch at one end of the damping resistor. In a passive damping network without a switch, the transmission efficiency decreases due to the parallel damping resistor. This invention controls the damping controller to provide a low level to disconnect the active damping switch of the active damping network before the pulse transmission controller completes its transmission, and controls the damping controller to provide a high level to close the active damping switch of the active damping network after the pulse transmission controller completes its transmission. The invention includes four main features: 1. A damping switch that delays the active damping pulse transmission by one cycle to control the damping controller to disconnect the active damping network with a low level, thereby improving transmission efficiency, reducing residual oscillation, and thus reducing the measurement blind zone; 2. An adaptive impedance matching network is introduced to adjust the impedance of different devices, which varies with temperature and aging, to match the impedance of the ranging circuit, effectively improving the sensitivity and transmission efficiency of the devices. High sensitivity can improve the distance measurement accuracy of the ranging circuit; 3. The invention also provides a pulse combination that sends short pulses (N pulses) at close range and long pulses (2N pulses) at long range, which can both improve the measurement range and reduce the measurement blind zone. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the ranging circuit of a piezoelectric MEMS ultrasonic sensor provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of a piezoelectric MEMS ultrasonic transducer array provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the high-voltage pulse drive circuit provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the adaptive impedance matching network provided in an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of the active damping network provided in an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of an active damping network switch provided in an embodiment of the present invention;

[0024] Figure 7 This is a schematic diagram of low-voltage pulse to high-voltage pulse waveform transformation provided in an embodiment of the present invention;

[0025] Figure 8 This is a schematic diagram of the transmit pulse and the active damping pulse provided in an embodiment of the present invention;

[0026] Figure 9 This is a schematic diagram of ultrasonic ranging time-of-flight measurement provided in an embodiment of the present invention;

[0027] Figure 10 This is a schematic diagram of the short pulse and long pulse transmission strategies provided in an embodiment of the present invention;

[0028] In this circuit, 1 is an MCU, 2 is a piezoelectric MEMS ultrasonic transducer, 3 is a high-voltage pulse drive circuit, 4 is an adaptive impedance matching network, 5 is an active damping network, 6 is a preamplifier, 7 is a bandpass filter, 8 is a time gain controller, and 9 is a temperature sensor; 1-1 is a pulse emission controller, 1-2 is a damping controller, 1-3 is an ADC, 1-4 is a residual vibration detector, 1-5 is a ranging module, and 1-6 is an impedance controller; 4-1 is a programmable capacitor, 4-2 is an inductor, and 4-3 is a digital IIC bus; 4-1-1 is a capacitor selection switch, and 4-1-2 is an impedance matching capacitor network; 5-1 is an active damping switch, and 5-2 is a damping resistor. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, the embodiment of the present invention employs a piezoelectric MEMS ultrasonic sensor ranging circuit, including: MCU1, high-voltage pulse drive circuit 3, adaptive impedance matching network 4, piezoelectric MEMS ultrasonic transducer 2, active damping network 5, preamplifier 6, bandpass filter 7 (BPF) and time gain controller 8 (TGC); MCU1 includes: pulse emission controller 1-1, damping controller 1-2, ADC (analog-to-digital converter) 1-3, residual vibration detector 1-4, ranging module 1-5 and impedance controller 1-6.

[0031] MCU1 is connected to high-voltage pulse drive circuit 3, active damping network 5, and adaptive impedance matching network 4 respectively. Active damping network 5 is connected in parallel with piezoelectric MEMS ultrasonic transducer 2. The output of high-voltage pulse drive circuit 3 is connected to the input of adaptive impedance matching network 4 and the input of preamplifier 6. The output of adaptive impedance matching network 4 is connected to the input of piezoelectric MEMS ultrasonic transducer 2. The output of piezoelectric MEMS ultrasonic transducer 2 is connected to the input of preamplifier 6. The output of preamplifier 6 is connected to the input of bandpass filter 7. The output of bandpass filter 7 is connected to the input of time gain controller 8. The output of time gain controller 8 is connected to MCU1.

[0032] The pulse transmitter controller 1-1 is connected to the high-voltage pulse drive circuit 3 and is used to control the high-voltage pulse drive circuit 3 to generate high-voltage pulses; the pulse transmitter controller 1-1 is connected to the damping controller 1-2 and is used to control the output of the damping controller 1-2 to be high or low level; the damping controller 1-2 is connected to the active damping network 5 and is used to control the opening and closing of the active damping network 5 (high level to open, low level to close); the impedance controller 1-6 is connected to the adaptive impedance matching network 4 and is used to control the impedance of the adaptive impedance matching network 4.

[0033] The input terminal of ADC1-3 is connected to the output terminal of time gain controller 8 to digitize the signal; the output terminal of ADC1-3 is connected to the input terminals of residual vibration detector 1-4 and ranging module 1-5 respectively. The residual vibration detector 1-4 is used to detect the amplitude of the signal, and the ranging module 1-5 is used to calculate the distance.

[0034] The preamplifier 6 is used to amplify the signal, the bandpass filter 7 (BPF) filters out signals other than the resonant frequency, and the time gain controller 8 is used to stabilize the signal amplitude.

[0035] The piezoelectric MEMS ultrasonic transducer 2 of this invention employs a transducer array composed of 6×6 elements, such as... Figure 2 As shown, the array can effectively improve the ultrasonic transceiver sound pressure and the signal-to-noise ratio of the echo signal in the ultrasonic ranging system. The piezoelectric MEMS ultrasonic transducer array uses an AlN thin film as the piezoelectric layer, and all array elements are arranged in parallel to form the transducer array.

[0036] The pulse emission controller 1-1 of MCU1 generates two pulses with a frequency of f1. One pulse is a positive pulse, and the other pulse is a negative pulse that is 180° out of phase with the positive pulse. The two pulses have the same number, the same frequency, and opposite phase.

[0037] like Figure 7 As shown, the high-voltage pulse drive circuit 3 is used to convert the two low-voltage pulses generated by the pulse emission controller 1-1 of MCU1 into high-voltage pulses; as Figure 3As shown, the high-voltage pulse drive circuit 3 includes: resistors R1~R5, MOSFETs M1~M2, capacitor C1, DC power supply DC, and pulse transformer T1; the input terminals of the pulse transformer T1 include pins 1, 2, and 3 in sequence, and the output terminals include pins 5 and 4 in sequence.

[0038] One end of resistor R4 is connected to a positive pulse, and the other end is connected to the gate of MOSFET M1. The source of MOSFET M1 is connected to one end of resistor R5, and the other end of resistor R5 is grounded. The drain of MOSFET M1 is connected to pin 1 of pulse transformer T1. One end of resistor R2 is connected to a negative pulse, and the other end is connected to the gate of MOSFET M2. The source of MOSFET M2 is connected to one end of resistor R3, and the other end of resistor R3 is grounded. The drain of MOSFET M2 is connected to pin 3 of pulse transformer T1. One end of resistor R1 is connected to DC power supply DC, and the other end is connected to pin 2 of pulse transformer T1 and one end of capacitor C1. The other end of capacitor C1 is grounded.

[0039] The DC power supply has a voltage of 12V, which can be changed according to actual needs.

[0040] When the positive pulse is high, the negative pulse is low, MOSFET M1 is turned on, and current flows from pin 2 to pin 1 of the N1 winding of pulse transformer T1. At this time, current is generated in the N3 winding. The voltage. When the positive pulse is low, the negative pulse is high, MOSFET M2 is turned on, and current flows from pin 2 to pin 3 of the N2 winding of pulse transformer T1. At this time, a voltage is generated in the N3 winding. The voltage. The waveforms of each phase of the pulse transformer are as follows: Figure 7 As shown. Number of turns in the winding of the pulse transformer. M is the amplification factor of the transformer. This high-voltage pulse circuit can convert the transmitted pulse into a peak value Vpp. A high-voltage pulse of volts. In ultrasonic ranging circuits, a high-voltage pulse can increase the emitted sound pressure of a piezoelectric MEMS transducer, thereby increasing the echo amplitude and improving the signal-to-noise ratio.

[0041] An adaptive impedance matching network can improve the energy transmission efficiency, system sensitivity, and ranging accuracy of the ranging circuit of this invention. A piezoelectric MEMS ultrasonic transducer can be equivalent to an RLC circuit, where its impedance changes drastically near the series-parallel resonant point at the resonant frequency. Its impedance amplitude and phase vary significantly with the driving frequency, manifesting as capacitance at non-resonant frequencies, resulting in very high impedance. Furthermore, inconsistencies in resonant frequency and impedance between different components due to temperature and aging can cause drift. Without impedance matching, problems such as low energy transmission efficiency, weak received signals, pulse waveform distortion, and changes in system Q-value can occur. However, using a fixed matching network can only achieve optimal matching at specific frequencies and load impedances. Once the piezoelectric MEMS ultrasonic transducer experiences the aforementioned drift, the impedance matching effect is significantly reduced. The adaptive impedance matching network 4 of this invention consists of a series of switch-controlled fixed capacitors and inductors, with the optimal matching impedance selected by the impedance controller of the MCU.

[0042] like Figure 4 As shown, the adaptive impedance matching network 4 includes a programmable capacitor 4-1 and an inductor 4-2; one end of the programmable capacitor 4-1 is connected to one end of the inductor 4-2, the other end of the programmable capacitor 4-1 is connected to the input terminal of the piezoelectric MEMS ultrasonic transducer 2, and the other end of the inductor 4-2 is connected to the output terminal of the high-voltage pulse drive circuit 3; the programmable capacitor 4-1 is connected to the impedance controller 1-6 of the MCU1 through the digital IIC bus 4-3, and the impedance controller 1-6 controls the programmable capacitor 4-1 to select the optimal matching capacitor.

[0043] The programmable capacitor 4-1 includes: a capacitor selection switch 4-1-1 (switches S1~S6) and an impedance matching capacitor network 4-1-2 (capacitors C0~C6); capacitors C0~C6 are connected in parallel, and switches S1~S6 are connected in series with the corresponding capacitors C1~C6, that is, switch S1 is connected in series with capacitor C1, switch S1 is connected in series with capacitor C1, ..., switch S6 is connected in series with capacitor C6; the capacitor selection switch 4-1-1 is connected to the control terminal of the programmable capacitor 4-1, and the two ends of capacitor C0 are connected to the capacitor output terminal of the programmable capacitor 4-1.

[0044] like Figure 5 , Figure 6 As shown, the active damping network 5 includes: an active damping switch 5-1 and a damping resistor 5-2 (R_damp); one end of the active damping switch 5-1 is connected to one end of the damping resistor 5-2, the other end of the active damping switch 5-1 is connected to the input terminal of the piezoelectric MEMS ultrasonic transducer 2, and the other end of the damping resistor 5-2 is connected to the output terminal of the piezoelectric MEMS ultrasonic transducer 2; the active damping switch 5-1 is connected to the damping controller 1-2 of the MCU1, and its closing and opening are controlled by the damping controller 1-2 of the MCU1.

[0045] The active damping switch 5-1 includes: resistors R1~R9, transistors Q1~Q4, power supply VCC, power supply VSS, and power supply VDD;

[0046] Damping controllers 1-2 are connected to one end of resistor R1, one end of resistor R4, and the source of transistor Q1, respectively. The other end of resistor R4 and the gate of transistor Q1 are connected to power supply VCC. The drain of transistor Q1 is connected to one end of resistor R5 and one end of resistor R8, respectively. The other end of resistor R5 is connected to power supply VDD. The other end of resistor R8 is connected to one end of resistor R9 and the gate of transistor Q3, respectively. The other end of resistor R9 and the source of transistor Q3 are grounded and connected to the input terminal of piezoelectric MEMS ultrasonic transducer 2.

[0047] The other end of resistor R1 is connected to one end of resistors R2 and R3 respectively. The other end of resistor R2 is connected to power supply VSS. The other end of resistor R3 is connected to the gate of transistor Q2. The source of transistor Q2 is connected to power supply VSS. The drain of transistor Q2 is connected to one end of resistors R6 and R7 respectively. The other end of resistor R6 is grounded. The other end of resistor R7 is connected to the gate of transistor Q4. The drain of transistor Q4 is connected to one end of damping resistor 5-2. The source of transistor Q4 is connected to the drain of transistor Q3. The other end of damping resistor 5-2 is connected to the output terminal of piezoelectric MEMS ultrasonic transducer 2.

[0048] The voltages of power supply VCC, power supply VSS, and power supply VDD are 3.3V, -5V, and 5V, respectively.

[0049] like Figure 8 As shown, the MCU's pulse transmitter controller 1-1 transmits N pulses. After completing the transmission of N pulses, it delays for half a cycle and then sends N / 5 pulses. These pulses are called active damping pulses.

[0050] When the MCU's damping controller 1-2 outputs a low level, transistors Q1 and Q2 are off, and transistors Q3 and Q4 are also off, at which point the active damping switch 5-2 is open. When the MCU's damping controller 1-2 outputs a high level, transistors Q1 and Q2 are on, and transistors Q3 and Q4 are on, at which point the active damping switch 5-2 is closed. The active damping network 5 generates heat through the damping resistor R_damp, reducing the ringing generated by the piezoelectric MEMS ultrasonic transducer array. Furthermore, since the active damping pulse is out of phase with the transmitted pulse, when the active damping switch 5-2 is closed, the active damping pulse applied to both ends of the transducer array can further reduce the residual vibration of the piezoelectric MEMS ultrasonic transducer array, thereby reducing the measurement blind zone of the ranging system of this invention and improving the measurement range.

[0051] On the other hand, embodiments of the present invention employ a ranging method based on the above-mentioned piezoelectric MEMS ultrasonic sensor ranging circuit, comprising:

[0052] S1. Set the capacitor of the adaptive impedance matching network 4 according to the ranging circuit of the piezoelectric MEMS ultrasonic sensor;

[0053] The capacitors for setting the adaptive impedance matching network 4 include:

[0054] S11. Fix the distance between the piezoelectric MEMS ultrasonic transducer 2 and the metal plate under test. Use impedance controller 1-6 to set the capacitance of the adaptive impedance matching network 4 to the initial capacitance C0. Use damping controller 1-2 to disconnect the active damping switch of the active damping network 5.

[0055] Setting the capacitor of the adaptive impedance matching network 4 to the initial capacitor C0 using impedance controllers 1-6 includes: disconnecting all switches of capacitor selection switch 4-1-1, thereby setting the capacitor of the adaptive impedance matching network 4 to the initial capacitor C0.

[0056] S12. Five short pulses with a frequency of f1 are emitted using the pulse emission controller 1-1. The short pulses are transmitted to the piezoelectric MEMS ultrasonic transducer 2 via the high voltage pulse drive circuit 3 and the adaptive impedance matching network 4.

[0057] S13. The piezoelectric MEMS ultrasonic transducer 2 generates ultrasonic waves with a vibration frequency of f1. The ultrasonic waves propagate through the air to the metal plate under test and are reflected back. The piezoelectric MEMS ultrasonic transducer 2 receives the reflected echo and converts the echo into an electrical signal, i.e., the ultrasonic echo signal.

[0058] S14. The ultrasonic echo signal is transmitted to the residual vibration detector 1-4 via the preamplifier 6, bandpass filter 7, time gain controller 8, and ADC1-3. The residual vibration detector 1-4 extracts the amplitude of the received signal.

[0059] S15. Determine whether all capacitors of the adaptive impedance matching network 4 have been traversed. If yes, use impedance controllers 1-6 to set the capacitors of the adaptive impedance matching network 4 to the capacitors corresponding to the highest amplitude. Otherwise, use impedance controllers 1-6 to set the capacitors of the adaptive impedance matching network 4 to the next capacitor and return to step S12.

[0060] The capacitor selection switch 4-1-1 of the adaptive impedance matching network 4 includes switches S1 to S6. By controlling the opening and closing of switches S1 to S6, the capacitor of the adaptive impedance matching network 4 can be adjusted. Therefore, all capacitors of the adaptive impedance matching network 4 include the capacitors corresponding to any combination of the opening and closing of switches S1 to S6. Setting the capacitor of the adaptive impedance matching network 4 as the next capacitor using the impedance controller 1-6 includes: using the impedance controller 1-6 to control switches S1 to S6, thereby setting the capacitor of the adaptive impedance matching network 4 as the next selectable capacitor.

[0061] S2, pulse transmitter controller 1-1 transmits N transmission pulses, including positive pulses and negative pulses. At the same time, damping controller 1-2 disconnects the active damping switch 5-2 of the active damping network 5 by giving a low level.

[0062] When a passive damping network without a switch transmits a pulse, the parallel damping resistor reduces the transmission efficiency. However, this invention controls the damping controller to provide a low level to disconnect the active damping switch of the active damping network before the pulse transmission controller completes the transmission of the pulse, and controls the damping controller to provide a high level to close the active damping switch of the active damping network after the pulse transmission controller completes the transmission of the pulse, thereby improving the transmission efficiency.

[0063] After the N transmission pulses are transmitted, the damping controller 1-2 sends a high level to close the active damping switch 5-2 of the active damping network 5. The pulse transmission controller 1-1 then sends N / 5 active damping pulses after a half-cycle delay. After the active damping pulses are transmitted, the damping controller 1-2 sends a low level after a one-cycle delay to open the active damping switch 5-2 of the active damping network 5.

[0064] Since the pulse transmitter controller 1-1 is connected to the damping controller 1-2, the damping controller 1-1 can determine whether the pulse of the pulse transmitter controller has been transmitted. It will give a low level before the transmission pulse is completed, give a high level after the transmission pulse is completed, and give a low level after a delay of one cycle after the active damping pulse is transmitted.

[0065] The active damping switch 5-2 disconnects after a delay of one cycle after the active damping pulse transmission is cut off. This reduces the residual vibration generated by the transducer without affecting the piezoelectric MEMS transducer's reception of the echo signal, thus significantly reducing the measurement blind zone of the ranging system.

[0066] S4. The transmitted pulse and the active damped pulse are transmitted to the piezoelectric MEMS ultrasonic transducer 2 through the high-voltage pulse drive circuit 3 and the adaptive impedance matching network 4. The piezoelectric MEMS ultrasonic transducer 2 emits ultrasonic waves, which are reflected back after propagating through the air to the metal plate under test. The piezoelectric MEMS ultrasonic transducer 2 receives the reflected echo and converts the echo into an electrical signal, i.e., the ultrasonic echo signal.

[0067] S5. The ultrasonic echo signal is transmitted through the preamplifier 6, bandpass filter 7 and time gain controller 8 and then input to ADC1-3 for digitization. The ranging module 1-5 calculates the distance based on the digitized ultrasonic echo signal.

[0068] Ranging modules 1-5 calculate the distance L based on the digitized ultrasonic echo signal, including:

[0069] Extract the echo envelope of the digitized ultrasound echo signal, such as Figure 9As shown, the timer calculates the flight time from the end of the transmitted pulse to the point of maximum amplitude of the echo envelope. The temperature data collected by temperature sensor 9 is T, and the speed of sound in the air at this time is... Measuring distance .

[0070] In one embodiment, such as Figure 10 As shown, with the optimal matching impedance parameters fixed, the MCU's pulse emission controller 1-1 emits N positive and anti-phase pulses in the first transmission, and then emits 2×N positive and anti-phase pulses in the second transmission. If the piezoelectric MEMS ultrasonic transducer 2 detects an echo signal in both the first and second transmissions, then only N positive and anti-phase pulses are emitted subsequently. If the piezoelectric MEMS ultrasonic transducer 2 does not detect an echo signal in the first transmission but does in the second, then only 2×N positive and anti-phase pulses are emitted subsequently. If neither the first nor the second transmission of the piezoelectric MEMS ultrasonic transducer 2 detects an echo signal, it indicates that the object being measured is outside the maximum measurement range. Increasing the number of emitted pulses is used for measuring long distances, while halving the number of pulses for short distances, ensuring measurability at long distances while reducing the blind zone at short distances.

[0071] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A piezoelectric MEMS ultrasonic sensor ranging circuit, characterized in that, include: MCU, high-voltage pulse drive circuit, adaptive impedance matching network, piezoelectric MEMS ultrasonic transducer, active damping network, preamplifier, bandpass filter and time gain controller. The MCU is connected to the high-voltage pulse drive circuit, the active damping network, and the adaptive impedance matching network, respectively. The active damping network is connected in parallel with the piezoelectric MEMS ultrasonic transducer. The output of the high-voltage pulse drive circuit is connected to the input of the adaptive impedance matching network and the input of the preamplifier. The output of the adaptive impedance matching network is connected to the input of the piezoelectric MEMS ultrasonic transducer. The output of the piezoelectric MEMS ultrasonic transducer is connected to the input of the preamplifier. The output of the preamplifier is connected to the input of the bandpass filter. The output of the bandpass filter is connected to the input of the time gain controller. The output of the time gain controller is connected to the MCU. The active damping network includes: an active damping switch and a damping resistor; one end of the active damping switch is connected to one end of the damping resistor, the other end of the active damping switch is connected to the input terminal of the piezoelectric MEMS ultrasonic transducer, and the other end of the damping resistor is connected to the output terminal of the piezoelectric MEMS ultrasonic transducer; the active damping switch is connected to the MCU. The MCU includes: a pulse emitter controller, a damping controller, and an impedance controller; The pulse transmitter controller is connected to the high-voltage pulse drive circuit and is used to control the high-voltage pulse drive circuit to generate high-voltage pulses; the pulse transmitter controller is connected to the damping controller and is used to control the output of the damping controller to be high or low level. The damping controller is connected to the active damping network and is used to control the active damping network to turn on or off. The impedance controller is connected to the adaptive impedance matching network and is used to control the impedance of the adaptive impedance matching network. The high-voltage pulse drive circuit includes: resistors R1~R5, MOSFETs M1~M2, capacitor C1, DC power supply DC, and pulse transformer T1; the input terminals of pulse transformer T1 include pins 1, 2, and 3 in sequence, and the output terminals include pins 5 and 4 in sequence. One end of resistor R4 is connected to the positive pulse, and the other end is connected to the gate of MOSFET M1. The source of MOSFET M1 is connected to one end of resistor R5, and the other end of resistor R5 is grounded. The drain of MOSFET M1 is connected to pin 1 of pulse transformer T1. One end of resistor R2 is connected to the negative pulse, and the other end is connected to the gate of MOSFET M2. The source of MOSFET M2 is connected to one end of resistor R3, and the other end of resistor R3 is grounded. The drain of MOSFET M2 is connected to pin 3 of pulse transformer T1. One end of resistor R1 is connected to the DC power supply DC, and the other end is connected to pin 2 of pulse transformer T1 and one end of capacitor C1, with the other end of capacitor C1 grounded. The active damping switch includes: resistors R1~R9, transistors Q1~Q4, power supply VCC, power supply VSS, and power supply VDD; The damping controller is connected to one end of resistor R1, one end of resistor R4, and the source of transistor Q1. The other end of resistor R4 and the gate of transistor Q1 are connected to power supply VCC. The drain of transistor Q1 is connected to one end of resistor R5 and one end of resistor R8. The other end of resistor R5 is connected to power supply VDD. The other end of resistor R8 is connected to one end of resistor R9 and the gate of transistor Q3. The other end of resistor R9 and the source of transistor Q3 are grounded and connected to the input terminal of the piezoelectric MEMS ultrasonic transducer. The other end of resistor R1 is connected to one end of resistors R2 and R3 respectively. The other end of resistor R2 is connected to power supply VSS. The other end of resistor R3 is connected to the gate of transistor Q2. The source of transistor Q2 is connected to power supply VSS, and the drain is connected to one end of resistors R6 and R7 respectively. The other end of resistor R6 is grounded. The other end of resistor R7 is connected to the gate of transistor Q4. The drain of transistor Q4 is connected to one end of damping resistor. The source of transistor Q4 is connected to the drain of transistor Q3. The other end of damping resistor is connected to the output terminal of piezoelectric MEMS ultrasonic transducer.

2. The piezoelectric MEMS ultrasonic sensor ranging circuit according to claim 1, characterized in that, The MCU also includes: an ADC, an aftershock detector, and a ranging module; the input of the ADC is connected to the output of the time gain controller, and the output of the ADC is connected to the input of the aftershock detector and the ranging module respectively; wherein, the ADC is an analog-to-digital converter.

3. The piezoelectric MEMS ultrasonic sensor ranging circuit according to claim 1, characterized in that, The MCU's pulse emission controller generates two pulses, one of which is a positive pulse and the other is a negative pulse. The two pulses have the same number, the same frequency, and opposite phase.

4. The piezoelectric MEMS ultrasonic sensor ranging circuit according to claim 1, characterized in that, The adaptive impedance matching network includes a programmable capacitor and an inductor; one end of the programmable capacitor is connected to one end of the inductor, the other end of the programmable capacitor is connected to the input of the piezoelectric MEMS ultrasonic transducer, and the other end of the inductor is connected to the output of the high-voltage pulse drive circuit; the programmable capacitor is connected to the impedance controller.

5. The piezoelectric MEMS ultrasonic sensor ranging circuit according to claim 1, characterized in that, The active damping switch is connected to the damping controller.

6. A ranging method based on the piezoelectric MEMS ultrasonic sensor ranging circuit according to any one of claims 1 to 5, characterized in that, include: S1. Set the capacitance of the adaptive impedance matching network according to the ranging circuit of the piezoelectric MEMS ultrasonic sensor; S2. The pulse transmitter controller transmits N transmission pulses, while the damping controller disconnects the active damping switch of the active damping network by sending a low level signal. S3. After the N transmission pulses are transmitted, the damping controller sends a high level to close the active damping switch of the active damping network. The pulse transmission controller then sends N / 5 active damping pulses after a half-cycle delay. After the active damping pulse is emitted, the damping controller delays for one cycle to disconnect the active damping switch of the active damping network by sending a low level. S4. The transmitted pulse and the active damped pulse are transmitted to the piezoelectric MEMS ultrasonic transducer through the high-voltage pulse drive circuit and the adaptive impedance matching network. The piezoelectric MEMS ultrasonic transducer generates ultrasonic waves. The ultrasonic waves propagate through the air to the metal plate under test and are reflected back. The piezoelectric MEMS ultrasonic transducer receives the reflected echo and converts the echo into an electrical signal, i.e., the ultrasonic echo signal. S5. The ultrasonic echo signal is transmitted to the ADC for digitization via a preamplifier, bandpass filter and time gain controller. The ranging module calculates the distance based on the digitized ultrasonic echo signal.

7. The ranging method according to claim 6, characterized in that, Setting the capacitors in the adaptive impedance matching network includes: S11. Fix the distance between the piezoelectric MEMS ultrasonic transducer and the metal plate under test, use an impedance controller to set the capacitance of the adaptive impedance matching network to the initial capacitance, and use a damping controller to disconnect the active damping switch of the active damping network. S12. A short pulse is emitted using a pulse emission controller. The short pulse is transmitted to the piezoelectric MEMS ultrasonic transducer via a high-voltage pulse drive circuit and an adaptive impedance matching network. S13. The piezoelectric MEMS ultrasonic transducer generates ultrasonic waves. The ultrasonic waves propagate through the air to the metal plate being tested and then reflect back. The piezoelectric MEMS ultrasonic transducer receives the reflected echo and converts the echo into an electrical signal, i.e., the ultrasonic echo signal. S14. The ultrasonic echo signal is transmitted to the residual vibration detector via a preamplifier, bandpass filter, time gain controller, and ADC. The residual vibration detector extracts the amplitude of the received signal. S15. Determine whether all capacitors of the adaptive impedance matching network have been traversed. If yes, use the impedance controller to set the capacitor of the adaptive impedance matching network to the capacitor corresponding to the highest amplitude. Otherwise, use the impedance controller to set the capacitor of the adaptive impedance matching network to the next capacitor and return to step S12.

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