Signal acquisition and wireless transmission system based on voltage dependent sensor

Abstract

The invention provides a signal acquisition and wireless transmission system based on a piezoelectric pressure-sensitive sensor. The signal acquisition and wireless transmission system comprises a piezoelectric signal acquisition circuit, a capacitance signal acquisition module, a low-power-consumption control module and a miniaturized integrated design, the piezoelectric signal acquisition circuit comprises a charge amplifier (OPA4340) and a band-pass filter (10Hz-1kHz); the capacitance signal acquisition unit comprises an ultrahigh-precision capacitance digital converter (PCAP01 chip) and a low-pass filter (0-10Hz); the low-power-consumption control module comprises an intermittent transmission protocol (adjustable data packing interval) of a Bluetooth module (nRF52840); the miniaturized integrated design comprises a flexible PCB (Printed Circuit Board) substrate and a module stacking layout; key elements (such as an ADC and a filter) are packaged by QFN (Quad Flat No-lead) so as to reduce the volume. Based on the technical scheme of the invention, the intelligent degree and the signal precision of the sensor circuit can be effectively improved, the power consumption and the parasitic capacitance interference are reduced, and the size is reduced.

Description

Technical Field

[0001] The present invention relates to the technical fields of intelligent sensors, intelligent sensor systems, and wearable electronic devices, and particularly to a signal acquisition and wireless transmission system for a flexible piezoelectric and piezoresistive sensor, which is applicable to the fields of attitude recognition, real-time motion monitoring, and other wearable devices containing sensors that need to be worn for a long time. Background Art

[0002] The prior art related to the present invention is divided into three parts: piezoelectric signal measurement, piezoresistive signal measurement (herein, the piezoresistive signal specifically refers to the capacitance signal, that is, the capacitance value of the sensor material changes with pressure, hereinafter simply referred to as the capacitance signal), and Bluetooth wireless transmission system.

[0003] The first part: Piezoelectric signal measurement. The general idea of the circuit design of a piezoelectric sensor is as follows: Piezoelectric material → Charge amplifier → Low-pass filter → Two-stage amplification → ADC → MCU → Wireless module. First, the piezoelectric signal is collected through a charge amplifier or a high-input impedance operational amplifier, and the noise is eliminated by combining with a low-pass filter. Subsequently, two-stage amplification and DC biasing are used to adapt to the ADC input, and then high-resolution analog-to-digital conversion is performed to digitize the weak signal. Or a charge-voltage hybrid amplification mode is adopted, with a charge-sensitive amplifier based on CMOS technology in the front stage and a chopper-stabilized instrumentation amplifier in the rear stage. In terms of the power supply scheme, the system can select a flexible thin-film lithium battery as the main power source. The wireless transmission module preferably selects low-power Bluetooth solutions such as nRF52832, and optimizes the transmission efficiency and energy consumption by adapting the packet length and connection interval. The entire system adopts a dynamic power management strategy to intelligently adjust the supply voltage and clock frequency of each module according to the working mode, so as to meet the requirements of long-term stability in medical monitoring scenarios and the special requirements of real-time performance in motion capture applications.

[0004] The second part: Capacitance signal measurement. The mainstream options for existing capacitance signal measurement include measurement of switch charge and discharge type, AC bridge type, operational amplifier type, and resonant type. Among them, the switch charge and discharge type is based on the charge and discharge time constant of the RC circuit. By controlling the switch to charge and discharge the capacitor periodically, the time required for the measured voltage to reach a specific threshold is measured. The AC bridge type utilizes the balance condition of the AC bridge. The capacitor is used as one arm of the bridge, and the known impedance (such as a standard capacitor and resistor) is adjusted to balance the bridge (the galvanometer reading is zero). The operational amplifier type uses an operational amplifier to construct a circuit to convert the capacitance value into a measurable electrical signal, or builds a circuit similar to that with the function of an operational amplifier by itself. The resonant type utilizes the internal counter of the microprocessor. Based on the LC resonant frequency, the measured capacitor and a known inductor form a resonant circuit. The signal source frequency is adjusted to the resonant point (the current is the largest), and the capacitance value is calculated through a formula.

[0005] Part 3: Wireless signal transmission circuit. The current microprocessor technology solutions for wearable piezoelectric / capacitive sensors mainly adopt low-power and high-integration designs. SoC chips with integrated high-precision ADC (and programmable gain amplifier (PGA)) directly process weak signals, and combine Cortex-M series MCU (mainly STM32L4 / nRF5340) to achieve local filtering and feature extraction. Some solutions introduce TinyML algorithms to reduce data transmission requirements; wireless transmission relies on BLE 5.0+ modules and adopts event-driven sampling strategies to optimize power consumption. Some designs integrate IMU (such as BMI270) for motion compensation to improve signal-to-noise ratio. The existing technical solutions for Bluetooth modules mainly revolve around the high sensitivity, low power consumption of sensors and the wireless transmission capabilities of Bluetooth modules. They mainly adopt low-power Bluetooth (BLE 5.0+) design, integrate high-precision ADC and signal conditioning circuits, and support real-time data transmission and multi-device connection. Typical solutions include: Nordic nRF52 series and TI CC2640 / CC2642R, etc.

[0006] The signal acquisition circuits of existing wearable devices generally have the following problems:

[0007] Low degree of intelligence: For example, the AC bridge type of capacitance measurement circuit requires the user to adjust parameters in real time to achieve balance, which is not suitable for wearable devices that need to collect data for a long time.

[0008] Insufficient accuracy: Due to power frequency interference, interference from the circuit itself, and interference from the electric field near the human body, the piezoelectric signal usually contains more noise, and the noise amplitude may even be higher than the expected signal amplitude.

[0009] High power consumption: Traditional circuits use a fixed sampling rate, which causes the microprocessor and wireless module to run at a continuous high load.

[0010] Low integration: Taking the capacitance measurement circuit as an example, the switch discharge type and the resonant type usually require a large external circuit, which is not easy to integrate. In addition, the entire signal acquisition and transmission system is usually designed in multiple modules, which makes it difficult to meet the miniaturization requirements of wearable devices. Summary of the invention

[0011] In response to the above-mentioned problems in the prior art, this application proposes a signal acquisition and wireless transmission system based on a piezoelectric voltage-sensitive sensor, which can improve the intelligence of the acquisition circuit so that the measurement range of the signal acquisition circuit covers the amplitude variation range of the target measurement signal. Accurate acquisition and noise suppression of piezoelectric and capacitive signals can be achieved. The overall power consumption of the system is reduced and the battery life of wearable devices is extended; while ensuring that different modules of the entire signal acquisition and transmission system do not interfere with each other, the circuit layout is optimized to the greatest extent possible to achieve high integration and miniaturization, and adapt to wearable devices.

[0012] The system of the present invention includes a piezoelectric signal acquisition circuit: a charge amplifier (OPA4340) + a band-pass filter (10 Hz - 1 kHz); capacitance signal acquisition: an ultra-high-precision capacitance digital converter (PCAP01 chip) + a low-pass filter (0 - 10 Hz); a low-power consumption control module: an intermittent transmission protocol of a Bluetooth module (nRF52840) (the data packet packing interval is adjustable); a miniaturized integrated design: using a flexible PCB substrate and a module stacked layout; key components (such as ADC, filter) are selected with QFN packages to reduce the volume.

[0013] The signal acquisition and wireless transmission system based on a piezoelectric and piezoresistive sensor of the present invention, in one embodiment, includes a piezoelectric signal acquisition circuit module; a capacitance signal acquisition module; a low-power consumption control module; a miniaturized integrated design module;

[0014] The piezoelectric signal acquisition circuit module includes a charge amplifier and a band-pass filter; the charge amplifier is OPA4340; the band-pass filter is 10 Hz - 1 kHz;

[0015] The capacitance signal acquisition module includes an ultra-high-precision capacitance digital converter and a low-pass filter; the capacitance digital converter is a PCAP01 chip; the low-pass filter is 0 - 10 Hz;

[0016] The low-power consumption control module includes an intermittent transmission protocol of a Bluetooth module; the Bluetooth module is nRF52840; the data packet packing interval of the intermittent transmission protocol is adjustable;

[0017] The miniaturized integrated design module uses a flexible PCB substrate and a module stacked layout; key components are selected with QFN packages; the key components include but are not limited to ADC and filters.

[0018] In one embodiment, the capacitance signal acquisition module is based on a PCAP01 high-precision capacitance digital converter, and is connected to the PC0 and PC1 pins of the PCAP01 through a differential mode, and at the same time, a high-precision reference capacitance is externally connected; the high-precision reference capacitance includes but is not limited to 10 pF NP0 / C0G.

[0019] In one embodiment, the PCAP01 calculates the capacitance value by the charge-discharge time ratio method, and the formula is tN / tref = CN / Cref. Combining with the internal 48-bit DSP, linear calibration and temperature compensation are performed on the data, and finally, the digital result is output with a 24-bit resolution; tN is the charge-discharge time of the measured capacitor, corresponding to the charge-discharge cycle of the capacitor CN to be measured, which is measured by the internal timer of the PCAP01; tref is the charge-discharge time of the reference capacitor, corresponding to the charge-discharge cycle of the internal known reference capacitor Cref, which is used as a reference value; CN is the value of the measured capacitor, the external capacitor to be measured, and its capacitance value is obtained by proportional calculation; Cref is the value of the reference capacitor, a high-precision reference capacitor, which is used to provide a proportional reference and usually has low temperature drift and high stability.

[0020] In one embodiment, the piezoelectric signal uses an ultra-low bias current operational amplifier to construct a charge amplifier; the capacitance signal uses a C-V conversion circuit and an active shielding technology.

[0021] In one embodiment, a signal conditioning section is further included. The signal conditioning section adopts a two-stage amplification architecture. First, it is preprocessed by an instrumentation amplifier with a high common-mode rejection ratio, and then the signal quality is optimized through a programmable gain amplifier and a 4th-order low-pass filter; for high-precision analog-to-digital conversion, a 24-bit Σ-Δ ADC or a dedicated capacitance digital converter is selected, and it is combined with a low-noise reference voltage source; the Σ-Δ ADC includes but is not limited to ADS131A04; the dedicated capacitance digital converter includes but is not limited to AD7153.

[0022] In one embodiment, a low-power wireless transmission module is included; the main control unit configures the PCAP01 register through the SPI interface and controls data acquisition and wireless transmission; the main control unit includes but is not limited to STM32L4.

[0023] In one embodiment, coaxial shielded traces are adopted; the PCB layout divides the analog and digital grounds and grounds them at a single point. At the same time, a 4.7 μF tantalum capacitor and a 100 nF ceramic capacitor are connected in parallel to the BUFFCAP pin.

[0024] In one embodiment, a dynamic power management strategy based on the STM32L4 main control is adopted, including a configurable intermittent transmission protocol: the data packet interval is adjustable from 1 ms to 10 s; the intelligent sampling mode of the PCAP01 chip, with 16 times of average sampling and a 20 μs reference period configured through the SPI register; a power supply noise suppression circuit, so that the overall power consumption of the system is <1.5 mW at a sampling rate of 100 Hz.

[0025] The above technical features can be combined in various suitable ways or replaced by equivalent technical features as long as the object of the present invention can be achieved.

[0026] A signal acquisition and wireless transmission system based on a piezoelectric voltage-sensitive sensor provided by the present invention has at least the following beneficial effects compared with the prior art:

[0027] Improved intelligence: The amplitude change range of the piezoelectric signal we need to collect is, and the capacitance signal change range we need to collect is 20 - 60 pF, and the final measurement range is 0 - 100 pF.

[0028] Improved signal accuracy: The signal-to-noise ratio (SNR) of the piezoelectric signal > 60 dB, and the resolution of the capacitance signal reaches 0.1 aF (attofarad).

[0029] Power consumption optimization: The system power consumption < 0.5 mW in the dynamic sleep mode.

[0030] Integrated design: The circuit board area < 10 cm 2 , and the thickness < 2 mm. Description of the Drawings

[0031] The present invention will be described in more detail below based on embodiments and with reference to the drawings. Among them:

[0032] Figure 1 Shows the principle block diagram of the signal acquisition and transmission system of the present invention;

[0033] Figure 2 Shows the final circuit layout wiring diagram of the present invention (using JLCPCB software); Detailed Embodiment

[0034] The present invention will be further described below in conjunction with the drawings.

[0035] The present invention provides a signal acquisition and wireless transmission system based on a piezoelectric voltage-sensitive sensor.

[0036] In one embodiment, as Figure 1 shown, an intelligent piezoelectric and capacitance signal acquisition circuit includes a capacitance signal acquisition based on the high-precision capacitance digital converter PCAP01, which is connected to the PC0 and PC1 pins of the PCAP01 through a differential mode to suppress the common-mode noise. At the same time, a high-precision reference capacitor (such as 10 pF NP0 / C0G) is externally connected to improve the measurement stability. The PCAP01 calculates the capacitance value by the charge and discharge time ratio method, and the formula is tN / tref = CN / Cref. Combining the internal 48-bit DSP to linearly calibrate and temperature-compensate the data, and finally output the digital result with a 24-bit resolution.

[0037] Among them, tN is the charge and discharge time of the measured capacitor, corresponding to the charge and discharge cycle of the capacitor CN to be measured, which is measured by the internal timer of PCAP01; tref is the charge and discharge time of the reference capacitor, corresponding to the charge and discharge cycle of the internal known reference capacitor Cref, serving as a reference value; CN is the value of the measured capacitor, the external capacitor to be measured, and its capacitance value is obtained through proportional calculation; Cref is the value of the reference capacitor, a high-precision reference capacitor, used to provide a proportional reference, usually having low temperature drift and high stability.

[0038] In one embodiment, for the high-precision anti-noise piezoelectric and capacitance signal acquisition circuit, in terms of the sensor interface, the piezoelectric signal uses an ultra-low bias current operational amplifier to construct a charge amplifier to achieve high-impedance matching, and the capacitance signal reduces the influence of parasitic capacitance through a C-V conversion circuit and active shielding technology. The signal conditioning section adopts a two-stage amplification architecture. First, it is preprocessed by an instrumentation amplifier with a high common-mode rejection ratio, and then the signal quality is optimized through a programmable gain amplifier and a 4th-order low-pass filter. High-precision analog-to-digital conversion selects a 24-bit Σ-Δ ADC (such as ADS131A04) or a dedicated capacitance digital converter (such as AD7153), in cooperation with a low-noise reference voltage source.

[0039] In one embodiment, the low-power wireless transmission module includes a main control unit (such as STM32L4) that configures the PCAP01 registers through the SPI interface (for example, register 2 is set to 0xC2FF460B to enable differential mode and internal and external compensation, and register 3 is set to 0xC3030010 to define a 20 μs reference period and 16 times of average sampling), and controls data acquisition and wireless transmission.

[0040] In one embodiment, as Figure 2 shown, for the integrated PCB layout and wiring, to cope with the dynamic noise of wearable devices, coaxial shielded traces need to be used in the hardware design to reduce parasitic capacitance. The PCB layout needs to separate the analog / digital ground and connect it to a single point ground. At the same time, the BUFFCAP pin is shunted with a 4.7 μF tantalum capacitor and a 100 nF ceramic capacitor to filter out power supply noise.

[0041] In one embodiment, the intelligent hybrid signal acquisition architecture: through the dual-channel design integrating a high-precision capacitance digital converter and a charge amplifier, it realizes the synchronous acquisition and collaborative processing of piezoelectric signals and capacitance signals; among them, PCAP01 is connected in differential mode and cooperates with NP0 / C0G reference capacitors, and based on the charge and discharge time ratio method, it realizes 48-bit DSP operation and 24-bit resolution output. At the same time, it has a built-in temperature compensation algorithm to improve environmental adaptability.

[0042] In one embodiment, a dynamic noise cancellation and miniaturization integration solution: At the hardware level, (1) coaxial shielded traces and analog / digital ground segmentation technology are adopted to reduce parasitic capacitance interference; (2) a 24-bit Σ-Δ ADC in a QFN package and a 4th-order active filter are cooperatively optimized for the signal-to-noise ratio; (3) a modular stacked layout on a flexible PCB substrate integrates a charge amplifier, a capacitance converter, and a Bluetooth module (nRF52840) three-dimensionally, and the overall thickness is controlled within 1.2 mm.

[0043] In one embodiment, an adaptive low-power control system: Based on the dynamic power management strategy of the STM32L4 main control, it includes (1) a configurable intermittent transmission protocol: the data packet interval is adjustable from 1 ms to 10 s; (2) the intelligent sampling mode of the PCAP01 chip, with 16 times of average sampling and a 20 μs reference period configured through the SPI register; (3) a power supply noise suppression circuit (a combination of a 4.7 μF tantalum capacitor and a 100 nF ceramic capacitor in parallel on the BUFFCAP pin), enabling the overall power consumption of the system to be <1.5 mW at a sampling rate of 100 Hz.

[0044] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A signal acquisition and wireless transmission system based on a piezoelectric and piezoresistive sensor, characterized in that Including a piezoelectric signal acquisition circuit module; a capacitance signal acquisition module; a low-power consumption control module; a miniaturized integrated design module; The piezoelectric signal acquisition circuit module includes a charge amplifier and a band-pass filter; The capacitance signal acquisition module includes an ultra-high-precision capacitance digital converter and a low-pass filter; The low-power consumption control module includes an intermittent transmission protocol of a Bluetooth module; the data packet packing interval of the intermittent transmission protocol is adjustable; The miniaturized integrated design module uses a flexible PCB substrate and a module stacking layout.

2. The signal acquisition and wireless transmission system based on a piezovoltage and piezoresistive sensor according to claim 1, characterized in that The capacitance signal acquisition module is based on a PCAP01 high-precision capacitance digital converter, and is connected to the PC0 and PC1 pins of the PCAP01 through a differential mode, and at the same time, a high-precision reference capacitor is externally connected.

3. The signal acquisition and wireless transmission system based on a piezoelectric voltage sensor according to claim 2, wherein, The PCAP01 calculates the capacitance value by the charge and discharge time ratio method, and the formula is tN / tref = CN / Cref. Combining the internal 48-bit DSP to linearly calibrate and temperature-compensate the data, and finally output the digital result with a 24-bit resolution; tN is the charge and discharge time of the measured capacitance, corresponding to the charge and discharge cycle of the capacitance CN to be measured, and is measured by the internal timer of the PCAP01; tref is the charge and discharge time of the reference capacitance, corresponding to the charge and discharge cycle of the internal known reference capacitance Cref, and is used as a reference value; CN is the measured capacitance value, the external capacitance to be measured, and its capacitance value is calculated by proportion; Cref is the reference capacitance value, a high-precision reference capacitance, which is used to provide a proportional reference and usually has low temperature drift and high stability.

4. The signal acquisition and wireless transmission system based on a piezoelectric voltage sensor according to claim 1, characterized in that, The piezoelectric signal uses an ultra-low bias current operational amplifier to construct a charge amplifier; the capacitance signal uses a C-V conversion circuit and an active shielding technology.

5. The signal acquisition and wireless transmission system based on a piezovoltage and piezoresistive sensor according to claim 1, characterized in that, It also includes a signal conditioning link. The signal conditioning link adopts a two-stage amplification architecture. First, it is preprocessed by an instrumentation amplifier with a high common-mode rejection ratio, and then the signal quality is optimized through a programmable gain amplifier and a 4th-order low-pass filter; For high-precision analog-to-digital conversion, a 24-bit Σ-Δ ADC or a dedicated capacitance digital converter is selected, and it is matched with a low-noise reference voltage source.

6. The signal acquisition and wireless transmission system based on a piezoelectric voltage sensor according to claim 1, characterized in that Including a low-power wireless transmission module; the main control unit configures the PCAP01 register through the SPI interface and controls data acquisition and wireless transmission.

7. The signal acquisition and wireless transmission system based on a piezoelectric voltage sensor according to claim 1, characterized in that, Coaxial shielded traces are adopted; the PCB layout divides the analog and digital grounds and grounds them at a single point. At the same time, the BUFFCAP pin is shunted with a 4.7 μF tantalum capacitor and a 100 nF ceramic capacitor.

8. The signal acquisition and wireless transmission system based on a piezoelectric voltage sensor according to claim 1, characterized in that Adopt a dynamic power consumption management strategy, including a configurable intermittent transmission protocol: the data packet packing interval is adjustable from 1 ms to 10 s; the intelligent sampling mode of the PCAP01 chip, and 16 times of average sampling and a 20 μs reference period are configured through the SPI register; A power supply noise suppression circuit enables the overall power consumption of the system to be <1.5 mW at a sampling rate of 100 Hz.

9. The signal acquisition and wireless transmission system based on a piezovoltage and piezoresistive sensor according to claim 1, characterized in that The ADC and filter are selected in QFN packages.

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