An electrochemical oxygen sensor detection circuit for wearable devices

Abstract

The application relates to the field of electrochemical signal processing, and particularly discloses a wearable-device-oriented electrochemical oxygen sensor detection circuit, which comprises a transimpedance amplification module, an active low-pass filtering module and a temperature calibration module.The transimpedance amplification module comprises an analog switch S1 and at least two feedback resistors with different resistance values, the feedback resistors are connected in parallel, the analog switch S1 is connected in series with the feedback resistors, the analog switch S1 is used for controlling the feedback resistors connected to the circuit, and the transimpedance amplification module is used for outputting a first voltage signal; the active low-pass filtering module is used for filtering the first voltage signal, filtering out thermal noise, power frequency interference and motion artifact noise, and obtaining a second voltage signal; the temperature calibration module is used for collecting temperature information; and a microcontroller is used for providing driving voltages for the transimpedance amplification module and the active low-pass filtering module, receiving the temperature information and the second voltage signal, and comparing the second voltage signal with a preset value. The technical scheme of the application has high precision, low power consumption and can reduce environmental interference.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical signal processing, in particular to an electrochemical oxygen sensor detection circuit for wearable devices. BACKGROUND

[0002] As a key physiological indicator directly reflecting the oxygen supply level of tissue microcirculation, partial pressure of oxygen (PtO2) has irreplaceable clinical value in intensive care, chronic wound healing monitoring, sports medicine, and high altitude medicine. For example, in the evaluation of tissue perfusion in shock patients, real-time PtO2 monitoring can accurately reflect the degree of tissue hypoxia; in the monitoring of diabetic foot ulcer healing, changes can directly reflect the improvement of microcirculation.

[0003] Traditional PtO2 detection relies on invasive Clark electrodes or fluorescent optical probes, which require piercing subcutaneous tissue or implanting sensors, and has limitations such as high risk of trauma, complex operation, high cost, and only single collection. With the development of wearable medical devices towards continuous monitoring, high-precision and low-trauma continuous PtO2 monitoring technology has become an urgent need for critical care and chronic disease management.

[0004] The performance improvement of current wearable electrochemical PtO2 monitoring devices is limited by the design of signal acquisition and conversion circuit. The core bottlenecks include: insufficient front-end noise suppression, traditional trans-impedance amplifiers lack anti-interference design, resulting in nanampere-level weak current signals being overwhelmed by thermal noise (4kTR), motion artifact noise (0.1-10Hz), power frequency interference (50Hz / 60Hz), etc.; narrow dynamic range, fixed gain trans-impedance amplifier circuit (TIA) has insufficient resolution (>1 mmHg / LSB) at low PtO2 (<20 mmHg) and is prone to saturation at high PtO2 (>100 mmHg); lack of real-time environmental compensation, no temperature / humidity sensor integrated to correct electrode drift, large cross-scene error; power consumption and precision imbalance, high-precision analog-to-digital converter (ADC) conflicts with limited battery capacity of wearable devices, making it difficult to meet the endurance requirements.

[0005] There is an electrochemical signal detection device on the market, which is composed of a controller module, an excitation signal module, a constant potential instrument module, a signal acquisition module, and a power module, which can realize the detection of electrochemical signals. Among them, the controller module is responsible for initializing hardware and data processing, the excitation signal module generates a bipolar excitation signal, the constant potential instrument module maintains the potential between the working electrode and the reference electrode constant, the signal acquisition module realizes sub-range detection (nA range 1GΩ, μA range 100kΩ, mA range 1kΩ) through different resistance feedback resistors, and the power module provides a bipolar power supply and a reference voltage.

[0006] However, the technical solution has significant defects in wearable scenarios: first, the power consumption is too high to adapt to wearable devices, and the complex circuit design results in a static power consumption of more than 500 mu A, while the commonly used button battery (capacity ≤ 500 mAh) of wearable devices cannot meet the endurance demand (less than 7 days); second, the temperature drift problem is not solved, and in nA-level weak current detection, environmental temperature fluctuations will cause detection error to increase; third, the range switching mechanism is imperfect, only the range switching through resistance grading is mentioned, the specific switching logic is not disclosed, and the signal jump problem during switching is not solved; fourth, the filter design does not target the noise in wearable scenarios, and specific noise such as motion artifacts and power frequency interference is not processed, and the signal-to-noise ratio (SNR) is low; fifth, the actual performance limitation of the operational amplifier is not considered, and when the working electrode voltage is less than the counter electrode voltage, large current input will cause the transimpedance amplification circuit to enter the nonlinear region, and the output result is unreliable.

[0007] In summary, the traditional electrochemical detection circuit is designed for laboratory scenarios and cannot solve the core contradiction between high precision and low power consumption in wearable scenarios and dynamic environment anti-interference, and a special electrochemical oxygen sensor detection circuit adapted to wearable devices is urgently needed. SUMMARY

[0008] The present application provides a wearable detection circuit for an electrochemical oxygen sensor with high precision, low power consumption, and reduced environmental interference.

[0009] To solve the above technical problems, the present application provides the following technical solutions:

[0010] An electrochemical oxygen sensor detection circuit for wearable devices, comprising:

[0011] A transimpedance amplification module, comprising an analog switch S1 and at least two feedback resistors with different resistance values, the feedback resistors being connected in parallel, the analog switch S1 being connected in series with the feedback resistors and being used to control the feedback resistors connected to the circuit and output a first voltage signal;

[0012] An active low-pass filter module for filtering the first voltage signal to remove thermal noise, power frequency interference and motion artifact noise and obtain a second voltage signal;

[0013] A temperature calibration module for collecting temperature information;

[0014] A microcontroller for providing driving voltages to the transimpedance amplification module and the active low-pass filter module, respectively, and receiving temperature information and the second voltage signal;

[0015] The microcontroller is used for receiving a second voltage signal and comparing with a preset value, and then controlling the analog switch S1 to realize switching of access of different feedback resistances according to a comparison result, and the microcontroller also pre-stores current-voltage linear regression coefficients of different temperature intervals, the microcontroller calls corresponding regression coefficients according to temperature information, calibrates the second voltage signal to obtain a calibrated current signal, and analyzes the calibrated current signal through a sliding window standard deviation calculation, a first-order linear difference and a fast Fourier transform to identify a rapid change stage of oxygen partial pressure, and switches a coarse sampling mode and a high-speed sampling mode according to the change stage.

[0016] The basic scheme principle and beneficial effects are as follows: through multi-module collaborative design, the present application is aimed at the signal acquisition and processing of an electrochemical oxygen sensor in a wearable scene. The microcontroller identifies the rapid change stage of oxygen partial pressure in real time through sliding window standard deviation calculation, first-order linear difference and fast Fourier transform, dynamically switches the coarse sampling and high-speed sampling modes, and adopts low-frequency coarse sampling to reduce invalid power consumption when the oxygen partial pressure is stable, and adopts high-frequency sampling to capture key signals when the oxygen partial pressure changes rapidly. This design avoids the continuous high power consumption of the timing sampling.

[0017] The temperature calibration module acquires the ambient temperature in real time, and the segmented calibration unit pre-stores current-voltage linear regression coefficients at different temperatures. The microcontroller calls corresponding coefficients according to the real-time temperature to offset the nonlinear influence of temperature. The analog switch of the transimpedance amplification module switches the feedback resistance under the control of the microcontroller, and the microcontroller monitors the filtered voltage signal through the voltage comparator, and automatically switches to the matched resistance (high resistance for small current to ensure resolution, and low resistance for large current to prevent saturation) when the signal approaches the threshold. The clear switching logic (based on voltage threshold judgment) reduces signal jumping and realizes adaptive matching of the range.

[0018] The active low-pass filter module is specially designed for noise in a wearable scene, retains the direct current / low-variation target signal of the oxygen sensor through low-pass characteristics, greatly attenuates thermal noise, power frequency interference and motion artifacts, improves the signal-to-noise ratio (SNR), and ensures effective extraction of nano-level weak signals. The microcontroller compares the filtered voltage signal in real time to avoid nonlinear distortion of the circuit caused by large current input, and ensures the reliability of the output result. The microcontroller can identify the rapid change of oxygen partial pressure through fast Fourier transform and first-order difference algorithm, and timely switches to the high-speed sampling mode, so that the response speed is improved compared with the timing sampling scheme, and the real-time monitoring of critical conditions such as shock and respiratory failure is applicable.

[0019] The detection accuracy and recognition accuracy are optimized, and the synergistic effect of temperature calibration, low-noise filtering and range adaptive switching improves the oxygen partial pressure detection accuracy and the tissue hypoxia state recognition accuracy based thereon.

[0020] The temperature calibration range and motion artifact resistance design enable the circuit to maintain stable output in complex scenes such as motion and temperature fluctuation, and adapt to multiple scene applications such as intensive care and sports medicine.

[0021] In conclusion, the application realizes high precision, low power consumption and reduces environmental interference.

[0022] Further, the application further comprises a Bluetooth transmission module for receiving the calibrated current signal, temperature information and device state processed by the microcontroller and transmitting them to an external terminal.

[0023] Further, the transimpedance amplification module further comprises an operational amplifier U1A and a capacitor C1, the inverting input end of the operational amplifier U1A is connected with the working electrode WE of the oxygen sensor and one end of the capacitor C1, the feedback resistors are connected in parallel between each other, the analog switch S1 is connected in series between the feedback resistors and is used for controlling the feedback resistors connected to the circuit, the other end of the capacitor C1 and the feedback resistors are connected with the output end of the operational amplifier U1A, and the output end of the operational amplifier U1A outputs a first voltage signal.

[0024] Further, the active low-pass filter module comprises a resistor R3, a resistor R4, a capacitor C2, a capacitor C3 and an operational amplifier U2A, the resistor R3, the resistor R4 and the capacitor C2 are connected in series with the output end of the operational amplifier U1A in sequence, and the capacitor C2 is grounded, the input end of the capacitor C3 is connected with the output end of R3, the output end of the capacitor C3 is connected with the inverting input end of the operational amplifier U2A and the output end of the operational amplifier U2A, the non-inverting input end of the operational amplifier U2A is connected with the output end of the resistor R4, and the output end of the operational amplifier U2A outputs a second voltage signal.

[0025] Further, the application further comprises a voltage follower module comprising an operational amplifier U3A and a capacitor C4, the inverting input end of the operational amplifier U3A is connected with the input end of the capacitor C4, the output end of the operational amplifier U3A is connected with the output end of the capacitor C4, the two ends of the capacitor C4 are short-circuited, and the output end of the operational amplifier U3A is connected with the counter electrode CE of the oxygen sensor.

[0026] Further, the microcontroller comprises a DAC_WE end, a DAC_CE end and an ADC input end; the DAC_WE end is connected with the non-inverting input end of the operational amplifier U1A, the ADC input end is connected with the output end of the operational amplifier U2A, and the DAC_CE end is connected with the non-inverting input end of the operational amplifier U3A.

[0027] Further, the feedback resistors of the transimpedance amplification module are two, which are a resistor R1 and a resistor R2, and the resistance value of the resistor R1 is less than that of the resistor R2; the voltage of the DAC_WE end is lower than that of the DAC_CE end.

[0028] Further, the resistance R3 is 4.7KΩ, the resistance R4 is 100KΩ, the capacitance C2 is 4.7uF, the capacitance C3 is 22uF, and the cut-off frequency is 0.72Hz; the period of the coarse sampling mode is t1, the period of the high-speed sampling mode is t2, and t2 < t1.

[0029] Further, the specific manner in which the dynamic sampling function identifies the rapid change stage of the oxygen partial pressure is as follows: a sliding window width m is set, and the standard deviation of the data in the window is calculated; when the standard deviation is between threshold 1 and threshold 2 for three consecutive times, the sampling mode is entered; after entering the judgment, the first-order difference is calculated, and if the n difference values in the window are greater than threshold 4, or the spectral intensity above the critical frequency F after FFT calculation is greater than threshold 3, the high-speed sampling mode is switched to.

[0030] Further, the minimum output swing of the operational amplifier U2A is V_OL, and when the second voltage signal is less than V_OL, the microcontroller outputs an invalid warning, and the invalid warning includes a current sampling data invalid identification; the temperature calibration module includes an NTC resistor and a fixed resistor R5, and the microcontroller calculates the NTC resistor value by voltage division, and then queries a preset temperature-resistance table to obtain temperature information. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a circuit diagram of a transimpedance amplification module and an active low-pass filtering module in an electrochemical oxygen sensor detection circuit for a wearable device.

[0032] Figure 2 It is a circuit diagram of a voltage follower module in an electrochemical oxygen sensor detection circuit for a wearable device.

[0033] Figure 3 It is a flowchart of a microcontroller implementing a dynamic sampling function in an electrochemical oxygen sensor detection circuit for a wearable device. DETAILED DESCRIPTION

[0034] The following will be further described in detail through specific embodiments:

[0035] An electrochemical oxygen sensor detection circuit for a wearable device includes a transimpedance amplification module, a voltage follower module, an active low-pass filtering module, a temperature calibration module, a microcontroller, and a Bluetooth transmission module.

[0036] The transimpedance amplification module (such as Figure 1The first voltage signal is outputted by the output terminal of the operational amplifier U1A. The oxygen sensor circuit shown in FIG. 1 includes an operational amplifier U1A, a capacitor C1, an analog switch S1 and two feedback resistors with different resistance values, the two feedback resistors are connected in parallel, the analog switch S1 is connected in series between the two feedback resistors and is used to control the feedback resistors connected to the circuit, and the first voltage signal is outputted; the inverting input terminal of the operational amplifier U1A is connected with the working electrode WE of the oxygen sensor and one end of the capacitor C1, the two feedback resistors are connected in parallel, the analog switch S1 is connected in series between the two feedback resistors and is used to control the feedback resistors connected to the circuit, the other end of the capacitor C1 and the feedback resistors are connected with the output terminal of the operational amplifier U1A, and the first voltage signal is outputted by the output terminal of the operational amplifier U1A.

[0037] The active low-pass filter module is used to filter the first voltage signal to filter out thermal noise, power frequency interference and motion artifact noise, and obtain a second voltage signal. The specific structure of the active low-pass filter module includes a resistor R3, a resistor R4, a capacitor C2, a capacitor C3 and an operational amplifier U2A, the resistor R3, the resistor R4 and the capacitor C2 are connected in series with the output terminal of the operational amplifier U1A in sequence, and the capacitor C2 is grounded, the input terminal of the capacitor C3 is connected with the output terminal of R3, the output terminal of the capacitor C3 is connected with the inverting input terminal of the operational amplifier U2A and the output terminal of the operational amplifier U2A, the non-inverting input terminal of the operational amplifier U2A is connected with the output terminal of the resistor R4, and the output terminal of the operational amplifier U2A outputs the second voltage signal. The resistance of the resistor R3 is 4.7KΩ, the resistance of the resistor R4 is 100KΩ, the capacitance of the capacitor C2 is 4.7uF, the capacitance of the capacitor C3 is 22uF, and the cut-off frequency is 0.72Hz; the period of the coarse sampling mode is t1, the period of the high-speed sampling mode is t2, and t2

[0038] The minimum output swing of the operational amplifier U2A is V_OL, when the second voltage signal is less than V_OL, the microcontroller outputs an invalid warning, and the invalid warning includes a current sampling data invalid identification.

[0039] The voltage follower module (as shown in FIG. 3) includes an operational amplifier U3A and a capacitor C4, the inverting input terminal of the operational amplifier U3A is connected with the input terminal of the capacitor C4, the output terminal of the operational amplifier U3A is connected with the output terminal of the capacitor C4, the two terminals of the capacitor C4 are short-circuited, and the output terminal of the operational amplifier U3A is connected with the counter electrode CE of the oxygen sensor. Figure 2 The temperature calibration module is used to collect temperature information. The temperature calibration module includes an NTC resistor and a fixed resistor R5, the microcontroller calculates the NTC resistor value by voltage division, and then queries a preset temperature-resistance value table to obtain the temperature information.

[0040]

[0041] ​A microcontroller is configured to provide driving voltage to the transimpedance amplification module and the active low-pass filter module respectively, and receive temperature information and the second voltage signal; the microcontroller comprises a DAC_WE terminal, a DAC_CE terminal and an ADC input terminal; the DAC_WE terminal is connected with the non-inverting input terminal of the operational amplifier U1A, the ADC input terminal is connected with the output terminal of the operational amplifier U2A, and the DAC_CE terminal is connected with the non-inverting input terminal of the operational amplifier U3A.

[0042] The microcontroller is configured to receive the second voltage signal and compare it with a preset value, and then control the analog switch S1 to switch the feedback resistance according to the comparison result; the microcontroller also pre-stores current-voltage linear regression coefficients of different temperature intervals, and calls the corresponding regression coefficient according to the temperature information to calibrate the second voltage signal to obtain a calibrated current signal; the calibrated current signal is analyzed by a sliding window standard deviation calculation, a first-order linear difference and a fast Fourier transform to identify a rapid change stage of oxygen partial pressure, and the coarse sampling mode and the high-speed sampling mode are switched according to the change stage.

[0043] The specific way in which the dynamic sampling function identifies the rapid change stage of oxygen partial pressure is as follows: the sliding window width is set to m, and the standard deviation of the data in the window is calculated; when the standard deviation is between threshold 1 and threshold 2 for three consecutive times, the sampling mode is judged; after the judgment, the first-order difference is calculated, and if the n difference values in the window are greater than threshold 4, or the spectral intensity above the critical frequency F after FFT calculation is greater than threshold 3, the high-speed sampling mode is switched to.

[0044] The Bluetooth transmission module is configured to receive the calibrated current signal processed by the microcontroller, the temperature information and the device status, and transmit them to an external terminal.

[0045] In specific use: mainly adapted to oxygen sensors based on electrochemical principle, especially suitable for oxygen sensors working in negative potential conditions (i.e. sensors with working electrode voltage less than that of the counter electrode), which can realize constant potential driving, signal acquisition and processing and data transmission of such sensors.

[0046] The signal flow of the detection circuit is as follows: the working electrode (WE) of the electrochemical oxygen sensor outputs a nanoampere-level current signal, the transimpedance amplification module converts the current signal into a first voltage signal, the active low-pass filter module filters the first voltage signal to obtain a second voltage signal, the microcontroller processes the second voltage signal (including range switching, over-range warning and temperature calibration), and after adjusting the sampling mode by the dynamic sampling strategy, the data is output through the Bluetooth transmission module.

[0047] As Figure 1As shown, the non-inverting terminal of the operational amplifier U1A is connected with the DAC_WE terminal of the DAC peripheral output of the microcontroller (MCU) to receive the working electrode bias voltage; and the inverting terminal is connected with the working electrode (WE) of the oxygen sensor to receive the nano-ampere level current signal output by the WE.

[0048] The analog switch S1 is connected in series with the feedback resistor R1 and the resistor R2 (in parallel between the feedback resistors), for controlling the feedback resistances of the access circuit, and the resistance value R1 < R2. When the resistor R1 is accessed, the range is larger but the resolution is lower; and when the resistor R2 is accessed, the range is smaller but the resolution is higher.

[0049] One end of the capacitor C1 is connected with the inverting terminal of the operational amplifier U1A, and the other end is connected with the output terminal thereof, for suppressing high-frequency noise.

[0050] Based on the virtual short characteristic of the operational amplifier, the voltage at the WE terminal is equal to the voltage at the DAC_WE terminal (denoted as ). Assuming that the accessed feedback resistance is , and the current output by the oxygen sensor is , then the output voltage (the first voltage signal, denoted as ) of the transimpedance amplification module satisfies:

[0051] .

[0052] As shown in Figure 2 , the voltage follower module realizes the driving of the counter electrode, including the operational amplifier U3A and the capacitor C4, the non-inverting terminal of the operational amplifier U3A is connected with the DAC_CE terminal of the DAC peripheral output of the microcontroller to receive the counter electrode bias voltage; the output terminal is connected with the counter electrode (CE) of the oxygen sensor, and the inverting terminal is short-circuited with the output terminal (the capacitor C4 is short-circuited between the two terminals, for stabilizing the output). The function is to stabilize the voltage at the CE terminal, by setting the voltage at the DAC_WE terminal to be less than the voltage at the DAC_CE terminal, to ensure that the sensor works in the negative potential condition (the voltage at the WE terminal < the voltage at the CE terminal), and to meet the working requirements of the electrochemical oxygen sensor.

[0053] As shown in Figure 1 , the active low-pass filter module includes the operational amplifier U2A, the resistor R3, the resistor R4, the capacitor C2 and the capacitor C3, the input terminal of which is connected with the output terminal of the transimpedance amplification module (for receiving the first voltage signal u_out1), for filtering out the thermal noise, the power frequency interference (50Hz / 60Hz) and the motion artifact noise (0.1-10Hz) in the signal.

[0054] The cut-off frequency ω0 of the filter satisfies:

[0055]

[0056] In this embodiment, R3=4.7KΩ, R4=100KΩ, C2=4.7uF, and C3=22uF are selected, and the calculated cutoff frequency is 0.72Hz. These parameters effectively preserve the DC / gradually varying target signal (frequency < 0.72Hz) output by the oxygen sensor and significantly attenuate high-frequency interference signals (frequency > 0.72Hz), resulting in a filtered second voltage signal. .

[0057] The microcontroller (MCU) is the core control unit of the circuit. Its peripherals include a DAC (providing DAC_WE and DAC_CE voltages) and an ADC (acquiring the second voltage signal). ) and voltage comparator interface.

[0058] The microcontroller's voltage comparator interface (a built-in functional module) receives the second voltage signal. And preset two threshold voltages ( , ).

[0059] when near (In high current scenarios) the microcontroller controls analog switch S1 to switch to feedback resistor R1 to expand the range (to avoid signal saturation).

[0060] when near (For low-current scenarios) the signal is switched to feedback resistor R2 to improve resolution (meeting the requirements for low oxygen partial pressure detection). The principle of range switching is based on the conversion relationship between current and voltage: assuming the ADC reference voltage is... If the number of bits is N, then the maximum measurable current is... Current resolution .

[0061] Since R1 < R2, when connecting R1 Larger range (larger measurement range), larger LSB (lower resolution); the opposite is true when connected to R2, thus achieving adaptive matching of "large range anti-saturation - small range high resolution".

[0062] Because operational amplifiers have a minimum output swing (denoted as...) When the input current is too large, it causes the second voltage signal to be affected. < At this time, operational amplifiers U1A and U2A will enter the nonlinear operating region, and the output results will be unreliable. The microcontroller will then... and In comparison, when < If the data is invalid, an invalid warning (including an invalid identifier for the current sampled data) should be output immediately to ensure the reliability of subsequent data.

[0063] The microcontroller provides a reference voltage (DACVREF) through a DAC peripheral, which is applied to a voltage dividing circuit composed of the NTC resistor and a fixed resistor R5; by collecting the voltage at the NTC_ADC end (i.e. the pin or port of the microcontroller connected to the voltage dividing circuit), the real-time resistance of the NTC resistor is calculated according to the voltage dividing formula, and then the current environmental temperature is obtained by querying the pre-set "NTC resistor-temperature table" (provided by the manufacturer or calibrated by oneself).

[0064] Since the feedback resistor value, operational amplifier bias current and other parameters are nonlinearly affected by temperature, the present application adopts segmented calibration.

[0065] The calibration range is the common working temperature of wearable devices (0-40℃), and a calibration interval is set every 5℃ (a total of 8 intervals: 0-5℃, 5-10℃,..., 35-40℃);

[0066] Calibration method: select a high-precision low-ppm resistor R_CA to simulate the sensor input current (analog current At each temperature point, input 0, 1 / 5 range, 2 / 5 range,..., full range for a total of 6 current values, and measure the corresponding second voltage signal ;

[0067] For each temperature interval, the linear coefficients of the current-voltage relationship in the interval are calculated by linear regression and intercept (such as k0, b0 for 0-5℃, k1, b1 for 5-10℃, and so on);

[0068] When the sensor is working, the microcontroller calls the and of the corresponding interval according to the environmental temperature collected by the NTC, and calculates the calibrated current signal through the formula to offset the temperature drift.

[0069] The dynamic sampling function is executed by the microcontroller, which identifies the rapid change phase of oxygen partial pressure through sliding window standard deviation calculation, first-order linear difference and fast Fourier transform (FFT), and adaptively switches between coarse sampling mode (period t1) and high-speed sampling mode (period t2, and t2 Figure 3

[0070] Coarse sampling mode (default), low sampling frequency (such as t1=10 seconds / time), set a sliding window with a width of m, and calculate the standard deviation of the data in the window after each sampling;

[0071] ​Mode judgment trigger, when the standard deviation of 3 times is between threshold 1 and threshold 2, enter the sampling mode judgment; if the standard deviation of 3 times is greater than threshold 2, determine the sensor abnormal and alarm;

[0072] High-speed sampling mode switching condition:

[0073] ① After entering the judgment, first calculate the first-order difference, if the n difference values in the window are greater than threshold 4, it means that the oxygen partial pressure changes rapidly, switch to high-speed sampling (such as t2=1 second / time);

[0074] ② If not meet ①, perform FFT calculation: do FFT on window data and normalize, if the spectral intensity sum above critical frequency F is greater than threshold 3, switch to high-speed sampling;

[0075] Restore coarse sampling mode: after entering high-speed sampling, if the standard deviation of 3 times is less than threshold 1, it means that the oxygen partial pressure is stable, restore the coarse sampling mode; if both conditions are not met, determine that it is a fluctuation interference, also restore the coarse sampling.

[0076] The above is only an embodiment of the present application, the application is not limited to this embodiment. The application is not limited to the field involved in this embodiment, and the specific structure and characteristics of the scheme known in the art are not described in detail. The ordinary skilled person in the art knows all the ordinary technical knowledge in the field of the application before the filing date or the priority date, can know all the prior art in the field, and has the ability to apply conventional experimental means before that date. The ordinary skilled person in the art can improve and implement the scheme based on their own ability under the guidance of this application. Some typical known structures or known methods should not be an obstacle for the ordinary skilled person in the art to implement the present application. It should be noted that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be considered as the protection scope of the present application. These will not affect the effect and practicality of the present application. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. An electrochemical oxygen sensor detection circuit for a wearable device, comprising: The application relates to a sensor signal processing circuit, which comprises the following parts: a transimpedance amplification module, which comprises an analog switch S1 and at least two feedback resistors with different resistance values, the feedback resistors are connected in parallel, the analog switch S1 is connected in series with the feedback resistors, is used for controlling the feedback resistors connected to the circuit, and outputs a first voltage signal; an active low-pass filter module, which is used for filtering the first voltage signal to remove thermal noise, power frequency interference and motion artifact noise, and obtains a second voltage signal; a temperature calibration module, which is used for collecting temperature information; a microcontroller, which is used for providing driving voltages for the transimpedance amplification module and the active low-pass filter module respectively, receiving the temperature information and the second voltage signal; wherein the microcontroller is used for receiving the second voltage signal, comparing the second voltage signal with a preset value, then controlling the analog switch S1 to realize switching of different feedback resistors connected to the circuit according to a comparison result, the microcontroller further pre-stores current-voltage linear regression coefficients of different temperature intervals, calls corresponding regression coefficients according to the temperature information, calibrates the second voltage signal to obtain a calibrated current signal, and analyzes the calibrated current signal through a sliding window standard deviation calculation, a first-order linear difference and a fast Fourier transform to identify a rapid oxygen partial pressure change stage, and switches a coarse sampling mode and a high-speed sampling mode according to the change stage; the transimpedance amplification module further comprises an operational amplifier U1A and a capacitor C1, the inverting input end of the operational amplifier U1A is connected with a working electrode WE of an oxygen sensor and one end of the capacitor C1, the feedback resistors are connected in parallel, the analog switch S1 is connected in series with the feedback resistors, is used for controlling the feedback resistors connected to the circuit, the other end of the capacitor C1 and the feedback resistors are connected with the output end of the operational amplifier U1A, and the output end of the operational amplifier U1A outputs the first voltage signal; the active low-pass filter module comprises a resistor R3, a resistor R4, a capacitor C2, a capacitor C3 and an operational amplifier U2A, the resistor R3, the resistor R4 and the capacitor C2 are connected in series with the output end of the operational amplifier U1A in sequence, the capacitor C2 is grounded, the input end of the capacitor C3 is connected with the output end of R3, the output end of the capacitor C3 is connected with the inverting input end of the operational amplifier U2A and the output end of the operational amplifier U2A, the non-inverting input end of the operational amplifier U2A is connected with the output end of the resistor R4, and the output end of the operational amplifier U2A outputs the second voltage signal; the microcontroller comprises a DAC_WE end, a DAC_CE end and an ADC input end; the DAC_WE end is connected with the non-inverting input end of the operational amplifier U1A, the ADC input end is connected with the output end of the operational amplifier U2A, and the DAC_CE end is connected with the non-inverting input end of the operational amplifier U3A; the method for identifying the rapid oxygen partial pressure change stage comprises the following steps: setting a sliding window width as m, calculating the standard deviation of data in the window; when the standard deviation is between a threshold value 1 and a threshold value 2 for three times continuously, entering a sampling mode judgment; after entering the judgment, a first-order difference is calculated first, if n difference values in the window are greater than a threshold value 4, or the spectral intensity above a critical frequency F after FFT calculation is greater than a threshold value 3, then the high-speed sampling mode is switched to. The minimum output swing of the operational amplifier U2A is V_OL, when the second voltage signal is less than V_OL, the microcontroller outputs an invalid warning, the invalid warning includes a current sampling data invalid identification; the temperature calibration module includes an NTC resistance and a fixed resistance R5, the microcontroller calculates the NTC resistance value through a voltage division mode, and then queries a preset temperature-resistance value table to obtain temperature information.

2. The electrochemical oxygen sensor detection circuit for wearable devices according to claim 1, wherein, The Bluetooth transmission module is further included, which is used for receiving the calibrated current signal, temperature information and device state processed by the microcontroller, and transmitting to an external terminal.

3. The electrochemical oxygen sensor detection circuit for wearable devices according to claim 2, wherein, The voltage following module further includes an operational amplifier U3A and a capacitor C4, the inverting input end of the operational amplifier U3A is connected with the input end of the capacitor C4, the output end of the operational amplifier U3A is connected with the output end of the capacitor C4, the two ends of the capacitor C4 are short-circuited, and the output end of the operational amplifier U3A is connected with the counter electrode CE of the oxygen sensor.

4. The electrochemical oxygen sensor detection circuit for wearable devices according to claim 3, wherein, The feedback resistors of the transimpedance amplification module are two, which are the resistor R1 and the resistor R2, and the resistance value of the resistor R1 is less than the resistance value of the resistor R2; the voltage of the DAC_WE end is lower than the voltage of the DAC_CE end.

5. The electrochemical oxygen sensor detection circuit for wearable devices according to claim 4, wherein, R3 is 4.7KΩ, R4 is 100KΩ, C2 is 4.7uF, C3 is 22uF, the cutoff frequency is 0.72Hz; the period of the coarse sampling mode is t1, the period of the high-speed sampling mode is t2, and t2 is less than t1. The minimum output swing of the operational amplifier U2A is V_OL, when the second voltage signal is less than V_OL, the microcontroller outputs an invalid warning, the invalid warning includes a current sampling data invalid identification; the temperature calibration module includes an NTC resistance and a fixed resistance R5, the microcontroller calculates the NTC resistance value through a voltage division mode, and then queries a preset temperature-resistance value table to obtain temperature information. The Bluetooth transmission module is further included, which is used for receiving the calibrated current signal, temperature information and device state processed by the microcontroller, and transmitting to an external terminal. The voltage following module further includes an operational amplifier U3A and a capacitor C4, the inverting input end of the operational amplifier U3A is connected with the input end of the capacitor C4, the output end of the operational amplifier U3A is connected with the output end of the capacitor C4, the two ends of the capacitor C4 are short-circuited, and the output end of the operational amplifier U3A is connected with the counter electrode CE of the oxygen sensor. The feedback resistors of the transimpedance amplification module are two, which are the resistor R1 and the resistor R2, and the resistance value of the resistor R1 is less than the resistance value of the resistor R2; the voltage of the DAC_WE end is lower than the voltage of the DAC_CE end. R3 is 4.7KΩ, R4 is 100KΩ, C2 is 4.7uF, C3 is 22uF, the cutoff frequency is 0.72Hz; the period of the coarse sampling mode is t1, the period of the high-speed sampling mode is t2, and t2 is less than t

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