Low-noise high-precision pressure measuring circuit

Abstract

The invention relates to a low-noise high-precision pressure measuring circuit which comprises a bridge type sensor, an alternating-current excitation signal source, a phase-sensitive detector, a low-pass filter, a reference signal source and a signal conditioning amplifier. The alternating current excitation signal source modulates a differential voltage signal generated by the bridge type sensor to a high-frequency alternating current excitation signal generated by the alternating current excitation signal source to obtain a high-frequency pressure signal; the high-frequency pressure signal is amplified by the signal conditioning amplifier to form a modulated signal; the phase-sensitive detector performs frequency mixing on the modulated signal and a reference signal generated by a reference signal source to obtain a frequency mixing signal; the frequency mixing signal is filtered by a low-pass filter to form a direct-current voltage signal for pressure measurement; the reference signal generated by the reference signal source and the high-frequency AC excitation signal generated by the AC excitation signal source have the same frequency. According to the circuit, signals are modulated to a high-frequency area with low noise energy to be processed by adopting alternating-current excitation and coherent detection technologies, the signals and noise are effectively separated, and extremely high measurement resolution and precision are achieved.

Description

Technical Field

[0001] This invention relates to the field of sensor signal detection and processing technology, and in particular to a low-noise, high-precision pressure measurement circuit. Background Technology

[0002] With the advancement of science and technology and the continuous development of engineering techniques, the precise measurement of physical quantities such as pressure, temperature, and flow rate has become a crucial technical requirement in modern industry, aerospace, medicine, and scientific research. Especially in fields such as aerospace and biomedicine, the accuracy requirements for sensors are even more stringent. To meet this demand, pressure sensors based on Wheatstone bridges are widely used. However, existing traditional DC bridge circuits have the following technical problems: 1. Severe low-frequency noise interference: When using a traditional DC voltage-excited Wheatstone bridge, the frequency bands of the bridge output signal and ambient noise overlap, causing the amplifier to amplify not only the effective signal but also low-frequency noise. Although a filter is present, it is difficult to effectively separate the signal and noise because they are located in the same frequency band.

[0003] 2. Limited Measurement Accuracy: In low signal-to-noise ratio conditions, especially when pressure sensors output weak signals, the presence of noise significantly affects the accuracy of measurement results. Traditional DC excitation methods cannot provide sufficient signal resolution in low-noise environments, impacting the execution of high-precision measurement tasks.

[0004] 3. Insufficient anti-interference capability: In some special applications, such as aerospace propulsion systems and satellite on-orbit monitoring, strong electromagnetic interference may exist around the measuring equipment. Traditional DC excitation schemes have poor suppression capability for high-frequency interference and are easily affected by external noise such as electromagnetic radiation and harmonic interference, resulting in unstable measurement results.

[0005] 4. Increasing Demand for High-Precision Measurement: In modern aerospace, military, and medical fields, measurement tasks increasingly require sensors to provide high-precision, low-noise real-time data. Existing traditional DC excitation circuits can no longer meet the growing requirements for accuracy and stability, necessitating new solutions to satisfy these demanding application needs.

[0006] In order to overcome the shortcomings of traditional circuits in low-noise environments and improve measurement accuracy and stability, it is particularly important to develop a new circuit structure with strong anti-interference ability and low noise performance. Summary of the Invention

[0007] To address the above-mentioned shortcomings in the existing technology, a low-noise, high-precision pressure measurement circuit is provided.

[0008] This invention provides a low-noise, high-precision pressure measurement circuit, comprising: a bridge sensor, an AC excitation signal source, a phase-sensitive detector, a low-pass filter, a reference signal source, and a signal conditioning amplifier; the AC excitation signal source modulates the differential voltage signal generated by the bridge sensor onto a high-frequency AC excitation signal generated by the AC excitation signal source to obtain a high-frequency pressure signal; the high-frequency pressure signal is amplified by the signal conditioning amplifier to form a modulated signal; the phase-sensitive detector mixes the modulated signal and the reference signal generated by the reference signal source to obtain a mixed signal; the mixed signal is filtered by the low-pass filter to form a DC voltage signal for pressure measurement; wherein the reference signal generated by the reference signal source has the same frequency as the high-frequency AC excitation signal generated by the AC excitation signal source.

[0009] Optionally, the output terminal of the AC excitation signal source is connected to the power supply terminal of the bridge sensor to provide a high-frequency AC excitation signal; the differential output terminal of the bridge sensor is connected to the input terminal of the signal conditioning amplifier; the output terminal of the signal conditioning amplifier is connected to the signal input terminal of the phase-sensitive detector; the output terminal of the reference signal source is connected to the reference input terminal of the phase-sensitive detector; the output terminal of the phase-sensitive detector is connected to the input terminal of the low-pass filter; and the output terminal of the low-pass filter serves as the output of the low-noise, high-precision pressure measurement circuit.

[0010] Optionally, the low-noise, high-precision pressure measurement circuit further includes: a phase adjustment circuit integrated into the reference signal source or connected between the reference signal source and the phase-sensitive detector; the phase adjustment circuit is used to adjust the phase of the reference signal so that the reference signal is phase-matched with the high-frequency AC excitation signal.

[0011] Optionally, the low-noise, high-precision pressure measurement circuit further includes a microprocessor unit; the input terminal of the analog-to-digital converter of the microprocessor unit is connected to the output terminal of the low-pass filter, and is used to perform digital processing, scaling transformation, temperature compensation, and display on the DC voltage signal.

[0012] Optionally, the bridge sensor is a Wheatstone bridge structure comprising four arms, each arm containing one or more varistors whose resistance value changes with the applied voltage.

[0013] Optionally, the AC excitation signal source is a signal generator capable of generating sine waves, square waves, or triangular waves, and the frequency range of the high-frequency AC excitation signal output by the AC excitation signal source is from 1 kHz to 1 MHz.

[0014] Optionally, the frequency range of the high-frequency AC excitation signal output by the AC excitation signal source is from 5 kHz to 100 kHz.

[0015] Optionally, the signal conditioning amplifier is a high input impedance, low noise instrumentation amplifier used to amplify the differential voltage signal output by the bridge sensor and suppress common-mode noise.

[0016] Optionally, the phase-sensitive detector is an analog multiplier or a switching mixer, and the phase-sensitive detector performs a multiplication operation between the modulated signal and the reference signal to achieve signal demodulation.

[0017] Optionally, the low-pass filter is an active low-pass filter, employing Butterworth, Chebyshev, or Bessel response types; the cutoff frequency of the low-pass filter is 1 / 10 to 1 / 100 of the frequency of the high-frequency AC excitation signal, in order to filter out the high-frequency components and out-of-band noise generated by the phase-sensitive detector.

[0018] The low-noise, high-precision pressure measurement circuit of the present invention has the following advantages: This invention provides a low-noise, high-precision pressure measurement circuit based on the principle of AC excitation and coherent detection. It uses AC excitation and coherent detection technology to modulate the signal to a high-frequency region with low noise energy for processing, thereby effectively separating the signal from the noise and achieving extremely high measurement resolution and accuracy, overcoming the aforementioned defects of existing DC-excited bridge measurement circuits. Attached Figure Description

[0019] Figure 1 It is a low-noise, high-precision pressure measurement circuit in the existing technology; Figure 2 This is a schematic diagram of a low-noise, high-precision pressure measurement circuit according to an embodiment of the present invention; Figure 3 This is another structural schematic diagram of the low-noise, high-precision pressure measurement circuit according to an embodiment of the present invention.

[0020] In the diagram: 1: Bridge sensor; 2: AC excitation signal source; 3: Phase-sensitive detector; 4: Low-pass filter; 5: Reference signal source; 6: Signal conditioning amplifier; 7: Phase adjustment circuit; 8: Microprocessor unit. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0022] This invention discloses a low-noise, high-precision pressure measurement circuit suitable for signal detection from various pressure sensors. This circuit modifies the operating mode of traditional DC bridge measurement circuits, using an AC excitation signal to drive the sensor bridge and incorporating coherent detection principles for signal processing. For conventional techniques, please refer to [link to previous documentation]. Figure 1 ,like Figure 1 As shown, traditional circuits use a fixed DC power supply Vcc to excite the bridge circuit, and the sensor output signal is amplified before being sent to the data acquisition system. However, due to the overlap of low-frequency noise with the signal, traditional circuits struggle to effectively filter out noise. Compared to traditional solutions, the low-noise, high-precision pressure measurement circuit of this invention can effectively reduce noise interference and improve measurement accuracy. The circuit introduces an AC excitation source and a phase-sensitive detection method, modulating the noise in the signal to a high frequency band, which is then effectively filtered out by a low-pass filter, thereby extracting a high-precision pressure signal. This technology is widely applicable to low-noise, high-precision measurements of pressure, temperature, and flow sensors, and has broad application prospects in aerospace, precision manufacturing, and biomedical fields. "Low noise" refers to noise levels below a preset noise threshold, and "high precision" refers to precision levels above the preset threshold.

[0023] Please refer to Figure 2 This invention provides a low-noise, high-precision pressure measurement circuit, comprising: a bridge sensor 1, an AC excitation signal source 2, a phase-sensitive detector 3, a low-pass filter 4, a reference signal source 5, and a signal conditioning amplifier 6.

[0024] The output of AC excitation signal source 2 is connected to the power supply of bridge sensor 1 to provide a high-frequency AC excitation signal; the differential output of bridge sensor 1 is connected to the input of signal conditioning amplifier 6; the output of signal conditioning amplifier 6 is connected to the signal input of phase-sensitive detector 3; the output of reference signal source 5 is connected to the reference input of phase-sensitive detector 3; the output of phase-sensitive detector 3 is connected to the input of low-pass filter 4; and the output of low-pass filter 4 serves as the output of a low-noise, high-precision pressure measurement circuit.

[0025] The corresponding working principle is as follows: AC excitation signal source 2 modulates the differential voltage signal generated by bridge sensor 1 onto the high-frequency AC excitation signal generated by AC excitation signal source 2 to obtain a high-frequency pressure signal; the high-frequency pressure signal is amplified by signal conditioning amplifier 6 to form a modulated signal; phase-sensitive detector 3 mixes the modulated signal and the reference signal generated by reference signal source 5 to obtain a mixed signal; the mixed signal is filtered by low-pass filter 4 to form a DC voltage signal for pressure measurement; wherein, the reference signal generated by reference signal source 5 has the same frequency as the high-frequency AC excitation signal generated by AC excitation signal source 2.

[0026] In this embodiment, the bridge sensor 1 is a Wheatstone bridge structure with four arms. Each arm contains one or more varistors, and the resistance value of the varistor changes with the applied voltage.

[0027] In this embodiment, the AC excitation signal source 2 is a signal generator capable of generating sine waves, square waves, or triangular waves, and the frequency range of the high-frequency AC excitation signal output by the AC excitation signal source 2 is from 1 kHz to 1 MHz.

[0028] As a preferred embodiment, the frequency range of the high-frequency AC excitation signal output by the AC excitation signal source 2 is 5kHz to 100kHz. This frequency range is used to define the high frequency in this specification, and the low frequency in this specification is defined as below 100Hz.

[0029] In this embodiment, the signal conditioning amplifier 6 is an instrumentation amplifier with high input impedance (input impedance higher than the threshold) and low noise (noise lower than the corresponding threshold), used to amplify the millivolt-level differential voltage signal output by the bridge sensor 1 and suppress common-mode noise.

[0030] In this embodiment, the phase-sensitive detector 3 is an analog multiplier or a switching mixer. The phase-sensitive detector 3 performs a multiplication operation between the modulated signal and the reference signal to achieve signal demodulation.

[0031] In this embodiment, the low-pass filter 4 is an active low-pass filter, employing Butterworth, Chebyshev, or Bessel response types; the cutoff frequency of the low-pass filter 4 is 1 / 10 to 1 / 100 of the frequency of the high-frequency AC excitation signal, in order to filter out the high-frequency components and out-of-band noise generated by the phase-sensitive detector 3.

[0032] In one embodiment, the low-noise, high-precision pressure measurement circuit further includes a phase adjustment circuit 7 integrated in the reference signal source 5 or connected between the reference signal source 5 and the phase-sensitive detector 3; the phase adjustment circuit 7 is used to adjust the phase of the reference signal so that the reference signal is phase-matched with the high-frequency AC excitation signal, thereby optimizing the output signal-to-noise ratio of coherent detection.

[0033] Optionally, the low-noise, high-precision pressure measurement circuit also includes: a microprocessor unit 8; the analog-to-digital converter input of the microprocessor unit 8 is connected to the output of the low-pass filter 4, and is used to perform digital processing, scaling transformation, temperature compensation, and display of the DC voltage signal.

[0034] The following describes a specific embodiment of the present invention. Please refer to [the relevant documentation]. Figure 2 and Figure 3 .

[0035] This embodiment provides a low-noise, high-precision pressure measurement circuit, including: a bridge sensor 1, an AC excitation signal source 2, a phase-sensitive detector 3, a low-pass filter 4, a reference signal source 5, a signal conditioning amplifier 6, an optional phase adjustment circuit 7, and an optional microprocessor unit 8.

[0036] Bridge sensor 1 is a Wheatstone full-bridge or half-bridge structure, with one or more piezoresistive elements in its bridge arms. This sensor converts changes in external pressure into changes in resistance, thereby outputting a weak differential voltage signal. Its power supply is connected to AC excitation signal source 2.

[0037] The AC excitation signal source 2 is one of the innovations of the circuit, replacing the traditional DC voltage source. This signal source generates a high-frequency AC excitation signal with stable frequency and constant amplitude, preferably a sine wave, with a frequency range between 5kHz and 100kHz. This high-frequency AC excitation signal modulates the effective pressure signal output by the bridge sensor 1 onto this excitation frequency and its harmonics, keeping its spectrum away from the low-frequency region dominated by 1 / f noise.

[0038] Signal conditioning amplifier 6 is connected to the output of bridge sensor 1. Its main function is to amplify the modulated high-frequency pressure signal. This amplifier needs to have high input impedance, low noise, and high common-mode rejection ratio (CMRR) to accurately amplify signals in the microvolt to millivolt range and suppress common-mode interference introduced during transmission.

[0039] Phase-sensitive detector 3, also known as the core of a lock-in amplifier or mixer, is a key component for achieving coherent detection. It has two inputs: one receives the modulated signal s(t) from signal conditioning amplifier 6; the other receives the reference signal r(t) from reference signal source 5. Phase-sensitive detector 3 performs a multiplication operation on the two signals. From a frequency domain perspective, this multiplication process is equivalent to shifting the spectrum of the modulated signal to the sum of the DC difference frequency and its second harmonic.

[0040] Reference signal source 5 is used to generate a reference signal with the same frequency as AC excitation signal source 2. To ensure optimal detection performance, the reference signal maintains strict synchronization with the high-frequency AC excitation signal. An optional phase adjustment circuit 7 can be integrated into reference signal source 5 or placed on its output path to finely adjust the phase of the reference signal to match the phase of the signal passing through the sensor and amplification links, thereby maximizing the DC component output of phase-sensitive detector 3.

[0041] Low-pass filter 4 is connected to the output of phase-sensitive detector 3. Its function is to filter out the high-frequency components generated after phase-sensitive detection, mainly the second harmonic components, as well as all broadband noise modulated into the high-frequency region. The cutoff frequency of the filter is set much lower than the excitation frequency, for example, less than 1 / 10 of the excitation frequency, allowing only DC or low-frequency slowly varying components proportional to the original pressure signal to pass through, thereby outputting a clean DC voltage signal with a high signal-to-noise ratio (SNR above the threshold).

[0042] like Figure 3 As shown, this invention uses an AC excitation source to provide a sinusoidal excitation signal (high-frequency AC excitation signal) to the bridge circuit. The modulated high-frequency pressure signal is represented as follows: Where A is the amplitude of the high-frequency pressure signal, ω is the frequency of the high-frequency pressure signal, α is the phase of the high-frequency pressure signal, and n(t) is the noise.

[0043] The reference signal is: Where B is the amplitude of the reference signal, The phase of the reference signal.

[0044] Multiplying the two in the multiplier yields: After the low-pass filter removes high-frequency components, it retains only: The signal and amplitude Proportional to the noise level, noise is effectively suppressed.

[0045] The microprocessor unit 8 acquires the DC voltage signal output by the low-pass filter 4 through its built-in ADC analog-to-digital converter, and performs digital processing, scaling transformation, temperature compensation, display, or uploading.

[0046] In this embodiment, the following key circuit design can be performed: 1. AC excitation signal source: The frequency range can be selected from 1kHz to 50kHz to avoid power frequency interference and ensure the stability of the excitation signal.

[0047] 2. Signal preamplifier (see...) Figure 3 ): Select a low-noise operational amplifier with an input bias current of less than 10 nA and a noise voltage density of less than 5 nV / √Hz.

[0048] 3. Multiplier (phase-sensitive detector): An analog four-quadrant multiplier, such as AD633, can be used, or a digital phase-locked loop amplifier can be implemented through DSP / FPGA.

[0049] 4. Low-pass filter: The cutoff frequency should be less than 1 / 10 of the excitation frequency. For example, when the excitation frequency is 10 kHz, the cutoff frequency should be less than 1 kHz.

[0050] Figure 3 This is another structural schematic diagram of the low-noise, high-precision pressure measurement circuit according to an embodiment of the present invention. Figure 3 In the middle, the reference signal source (5) adopts the AC excitation signal source (2), that is, the two are the same signal source, the multiplier is a phase-sensitive detector, the sensor measurement bridge (bridge sensor) and the multiplier are a signal conditioning amplifier, no phase adjustment circuit is used, and the microprocessor unit is not shown.

[0051] In summary, the beneficial effects of this invention compared to the prior art are as follows: 1. Excellent noise suppression capability: By modulating the signal to a high frequency, it effectively avoids the frequency bands with severe 1 / f noise and power frequency interference. The low-pass filtering after coherent detection can greatly attenuate these noises as well as any random noise that is not at the same frequency as the reference signal, and the system's noise floor is significantly reduced.

[0052] 2. High precision and high resolution: Due to the significant improvement in signal-to-noise ratio, the circuit can distinguish smaller pressure changes, and the measurement accuracy and resolution are far higher than those of traditional DC solutions.

[0053] 3. Strong anti-interference ability: It has natural immunity to common electromagnetic interference in the environment because incoherent interference signals are filtered out after phase-sensitive detection.

[0054] 4. Suppressing DC drift: The entire signal path processes AC signals, so the DC offset and drift of the amplifier will not be amplified by subsequent circuits, thus improving the long-term stability of the system.

[0055] 5. Wide applicability: This circuit principle is not only applicable to pressure sensors, but can also be widely used in other sensors based on resistance bridges to achieve low-noise and high-precision measurement, which has important engineering application value and market prospects.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-noise, high-precision pressure measurement circuit, characterized in that, include: Bridge sensor (1), AC excitation signal source (2), phase-sensitive detector (3), low-pass filter (4), reference signal source (5) and signal conditioning amplifier (6); The AC excitation signal source (2) modulates the differential voltage signal generated by the bridge sensor (1) onto the high-frequency AC excitation signal generated by the AC excitation signal source (2) to obtain a high-frequency pressure signal; the high-frequency pressure signal is amplified by the signal conditioning amplifier (6) to form a modulated signal; the phase-sensitive detector (3) mixes the modulated signal and the reference signal generated by the reference signal source (5) to obtain a mixed signal; the mixed signal is filtered by the low-pass filter (4) to form a DC voltage signal for pressure measurement; wherein, the reference signal generated by the reference signal source (5) has the same frequency as the high-frequency AC excitation signal generated by the AC excitation signal source (2).

2. The low-noise, high-precision pressure measurement circuit according to claim 1, characterized in that, The output of the AC excitation signal source (2) is connected to the power supply of the bridge sensor (1) to provide a high-frequency AC excitation signal; the differential output of the bridge sensor (1) is connected to the input of the signal conditioning amplifier (6); the output of the signal conditioning amplifier (6) is connected to the signal input of the phase-sensitive detector (3); the output of the reference signal source (5) is connected to the reference input of the phase-sensitive detector (3); the output of the phase-sensitive detector (3) is connected to the input of the low-pass filter (4); the output of the low-pass filter (4) serves as the output of the low-noise high-precision pressure measurement circuit.

3. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The low-noise, high-precision pressure measurement circuit further includes: a phase adjustment circuit (7) integrated into the reference signal source (5) or connected between the reference signal source (5) and the phase-sensitive detector (3); The phase adjustment circuit (7) is used to adjust the phase of the reference signal so that the reference signal is phase-matched with the high-frequency AC excitation signal.

4. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The low-noise, high-precision pressure measurement circuit also includes: a microprocessor unit (8); The analog-to-digital converter input of the microprocessor unit (8) is connected to the output of the low-pass filter (4) for digital processing, scaling transformation, temperature compensation and display of the DC voltage signal.

5. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The bridge sensor (1) is a Wheatstone bridge structure with four arms, each arm containing one or more varistors whose resistance value changes with the applied voltage.

6. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The AC excitation signal source (2) is a signal generator capable of generating sine waves, square waves or triangular waves, and the frequency range of the high-frequency AC excitation signal output by the AC excitation signal source (2) is from 1 kHz to 1 MHz.

7. The low-noise, high-precision pressure measurement circuit according to claim 6, characterized in that, The frequency range of the high-frequency AC excitation signal output by the AC excitation signal source (2) is 5kHz to 100kHz.

8. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The signal conditioning amplifier (6) is a high input impedance, low noise instrumentation amplifier used to amplify the differential voltage signal output by the bridge sensor (1) and suppress common-mode noise.

9. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The phase-sensitive detector (3) is an analog multiplier or a switching mixer. The phase-sensitive detector (3) performs a multiplication operation between the modulated signal and the reference signal to achieve signal demodulation.

10. The low-noise, high-precision pressure measurement circuit according to claim 2, characterized in that, The low-pass filter (4) is an active low-pass filter, using Butterworth, Chebyshev or Bessel response types; The cutoff frequency of the low-pass filter (4) is 1 / 10 to 1 / 100 of the frequency of the high-frequency AC excitation signal, so as to filter out the high-frequency components and out-of-band noise generated by the phase-sensitive detector (3).

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