Electrochemical sensor protection circuit

Abstract

According to the electrochemical sensor protection circuit provided by the invention, the output signal of the electrochemical sensor is amplified through the signal amplification module, and the reference voltage close to the maximum output voltage of the signal amplification module is generated through the reference voltage generation module; the voltage comparison module is used for comparing the real-time output voltage of the signal amplification module with the reference voltage generated by the reference voltage generation module, and when the real-time output voltage of the signal amplification module is larger than or equal to the reference voltage, the protection switch module is turned on to achieve short circuit of the positive electrode and the negative electrode of the electrochemical sensor. According to the electrochemical sensor protection circuit provided by the invention, when the output voltage of the operational amplifier is close to saturation or reaches saturation, an overload protection mechanism can be quickly triggered, and the electrochemical sensor is short-circuited, so that the operational amplifier is prevented from imbalance due to long-time saturation, and the positive and negative electrodes of the electrochemical sensor are prevented from accumulating voltage.

Description

Technical Field

[0001] The present application relates to the technical field of electrochemical sensor detection, and in particular to an electrochemical sensor protection circuit. Background Art

[0002] In the signal conditioning circuit of electrochemical sensors, operational amplifiers are often used to amplify the output signal of the sensor. The working principle of electrochemical sensors requires that a very small voltage difference be maintained between the positive and negative electrodes of the output to ensure the accuracy and stability of the measurement signal. However, in actual detection environments, the concentration of the substance being measured may far exceed the designed measurement range, which will cause the sensor to output a very large current. Excessive current will cause the operational amplifier to saturate or even become unregulated, which will lead to voltage accumulation between the positive and negative electrodes of the sensor, ultimately causing the sensor to malfunction or even be damaged.

[0003] At present, there is a circuit design in the signal conditioning circuit of the electrochemical sensor that connects a P-channel depletion-type metal-oxide-semiconductor field-effect transistor (MOSFET) (referred to as depletion-type PMOS tube) between the positive and negative electrodes of the sensor. Through this circuit design, when the system loses power, the depletion-type PMOS tube is turned on to short-circuit the positive and negative electrodes of the sensor, thereby effectively preventing the accumulation of voltage between the positive and negative electrodes of the sensor and realizing power-off protection for the sensor. However, for the situation where the concentration of the measured substance far exceeds the designed measurement range, resulting in the sensor outputting a very large current, the above circuit design still cannot avoid the problem of voltage accumulation between the positive and negative electrodes of the sensor after the operational amplifier is saturated and deregulated. Summary of the invention

[0004] An embodiment of the present invention provides an electrochemical sensor protection circuit to implement overload protection for the electrochemical sensor.

[0005] An embodiment of the present invention provides an electrochemical sensor protection circuit, comprising:

[0006] A signal amplification module, including an operational amplifier, connected to the positive electrode of the electrochemical sensor, and used to amplify the output signal of the electrochemical sensor to obtain an output voltage;

[0007] A reference voltage generating module, used for generating a reference voltage according to a supply voltage of a system power supply and a maximum output voltage of the signal amplifying module, wherein the reference voltage does not exceed the maximum output voltage;

[0008] A voltage comparison module, the input end of which is respectively connected to the output end of the signal amplification module and the reference voltage generation module, for comparing the output voltage with the reference voltage in real time;

[0009] The protection switch module is connected in parallel between the positive and negative electrodes of the electrochemical sensor and connected to the output end of the voltage comparison module, and is used to be turned on when the output voltage is greater than or equal to the reference voltage to short-circuit the positive and negative electrodes of the electrochemical sensor.

[0010] Optionally, the operational amplifier is a rail-to-rail output operational amplifier, and the power supply of the operational amplifier is determined based on the system power supply.

[0011] Optionally, the reference voltage generating module includes a first resistor R1 and a second resistor R2, one end of the R1 is connected to the system power supply, and the other end of the R1 is grounded through the R2;

[0012] The resistance ratio of the R1 to the R2 ranges from 1:4 to 1:9.

[0013] Optionally, the voltage comparison module includes a push-pull output comparator, and the power supply of the comparator is the system power supply;

[0014] The non-inverting input terminal of the comparator is connected to the voltage-dividing node of R1 and R2, the inverting input terminal of the comparator is connected to the output terminal of the signal amplification module, and the output terminal of the comparator is connected to the protection switch module.

[0015] Optionally, the protection switch module includes a depletion-type PMOS tube Q1;

[0016] The drain of Q1 is connected to the positive electrode of the electrochemical sensor, the source of Q1 is connected to the negative electrode of the electrochemical sensor, and the gate of Q1 is connected to the output end of the voltage comparison module.

[0017] Optionally, the negative electrode of the electrochemical sensor is connected to a reference potential Vref; the supply voltage of the system power supply is VCC, and the pinch-off voltage of Q1 is V OFF , then VCC, Vref and V OFF The following relationship is satisfied:

[0018]

[0019] Optionally, the protection switch module includes an enhanced PMOS tube Q2; the source of Q2 is connected to the positive electrode of the electrochemical sensor, the drain of Q2 is connected to the negative electrode of the electrochemical sensor, and the gate of Q2 is connected to the output end of the voltage comparison module.

[0020] Optionally, the negative electrode of the electrochemical sensor is connected to a reference potential Vref; the supply voltage of the system power supply is VCC, and the threshold voltage of Q2 is Vth , the constant potential difference between the positive and negative electrodes of the sensor is ΔV, then VCC, Vref, ΔV and V th The following relationship is satisfied:

[0021]

[0022] Furthermore, a dynamic control module is also arranged between the output end of the voltage comparison module and the protection switch module, which is used to control the protection switch module to conduct when the output voltage of the signal amplification module is greater than or equal to the reference voltage, or when the system power supply is powered off, so as to short-circuit the positive and negative electrodes of the electrochemical sensor.

[0023] Optionally, the dynamic control module includes a third resistor R3 and a fourth resistor R4, one end of R3 is connected to the system power supply, and the other end of R3 is connected to the output end of the voltage comparison module through R4.

[0024] The electrochemical sensor protection circuit provided by the embodiment of the present invention amplifies the output signal of the electrochemical sensor through a signal amplification module, generates a reference voltage close to the maximum output voltage of the signal amplification module through a reference voltage generation module, compares the real-time output voltage of the signal amplification module with the reference voltage generated by the reference voltage generation module through a voltage comparison module, and when the real-time output voltage of the signal amplification module is greater than or equal to the reference voltage, the positive and negative electrodes of the electrochemical sensor are short-circuited by turning on the protection switch module. The electrochemical sensor protection circuit provided by the embodiment of the present invention realizes real-time monitoring of the output voltage of the operational amplifier. When the output voltage of the operational amplifier is close to saturation or has reached saturation, the overload protection mechanism can be quickly triggered to short-circuit the electrochemical sensor, thereby avoiding the operational amplifier from being out of adjustment due to long-term saturation. In addition, through the overload protection mechanism, the voltage accumulation of the positive and negative electrodes of the electrochemical sensor is effectively avoided, thereby avoiding damage to the electrochemical sensor due to overload, thereby extending the service life of the electrochemical sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of an electrochemical sensor protection circuit provided by an embodiment of the present invention;

[0026] Figure 1a A structural example diagram of an electrochemical sensor protection circuit provided by an embodiment of the present invention;

[0027] Figure 1b A structural example diagram of another electrochemical sensor protection circuit provided by an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of the structure of an electrochemical sensor protection circuit provided by an embodiment of the present invention;

[0029] Figure 2a A structural example diagram of an electrochemical sensor protection circuit provided by an embodiment of the present invention;

[0030] Figure 2b This is a structural example diagram of another electrochemical sensor protection circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. It is also necessary to explain that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all structures.

[0032] It is understandable that according to the working characteristics of the electrochemical sensor, the electrochemical sensor generates a current signal through the oxidation / reduction reaction on the electrode surface. When working normally, the potential difference between the working electrode (positive electrode) and the reference electrode (negative electrode) is maintained by the constant potential circuit to form a stable electrochemical reaction environment, and the potential difference between the positive and negative electrodes is required to be very small, otherwise it will lead to inaccurate and unstable measurement signals. However, in the actual detection environment, the concentration of the measured substance may far exceed the designed measurement range, which will cause the sensor to output a very large current. Excessive current will cause the operational amplifier to saturate or even lose regulation, which will lead to voltage accumulation between the positive and negative electrodes of the sensor.

[0033] The essence of voltage accumulation is the coupling effect of circuit linearity destruction and electrochemical dynamic equilibrium imbalance. When the op amp fails due to overload, it cannot maintain the potential balance between the electrodes through feedback. At the same time, the electrochemical reaction rate inside the sensor is mismatched with the external circuit response speed, which eventually leads to charge accumulation and voltage offset between the sensor electrodes.

[0034] The accumulated voltage is continuously applied to the electrode, which may trigger unexpected electrolytic reactions (such as electrolyte decomposition or electrode material oxidation / reduction), resulting in decreased sensor sensitivity or shortened life. In addition, in the high-impedance electrolyte layer of the sensor, the residual charge is difficult to release by itself, which may cause electric field distortion and interfere with the accuracy of subsequent measurements. In addition, long-term residual voltage may change the catalytic activity or electrolyte ion distribution on the electrode surface, causing baseline current offset or nonlinear response.

[0035] In the prior art, in order to solve the problem of voltage accumulation of sensor electrodes when the system is powered off, a solution of connecting a depletion-type PMOS tube between the positive and negative electrodes of the sensor is proposed. By turning on the PMOS tube after the system is powered off, the impedance between the positive and negative electrodes is reduced to the level of the PMOS tube on-resistance (usually milliohm level), and the residual charge is quickly released through the low-resistance path, thereby eliminating the residual voltage. In addition, after short-circuiting, the potential difference between the positive and negative electrodes returns to zero, which can prevent the continuous electrolysis or side reactions of the electrolyte, thereby inhibiting the polarization reaction. In addition, short-circuiting can also prevent the damage of the sensitive electrode to the reverse current caused by external interference (such as electrostatic discharge).

[0036] However, the existing technical solutions cannot solve the problem that the sensor outputs a very large current because the concentration of the measured substance far exceeds the designed measurement range, which in turn causes voltage accumulation between the positive and negative electrodes of the sensor after the operational amplifier is saturated and deregulated.

[0037] The purpose of this application is to improve the existing technical solution so that when the output voltage of the signal amplification module is close to its maximum output voltage, the positive and negative electrodes of the sensor can be short-circuited, thereby achieving overload protection for the sensor.

[0038] Figure 1 Schematic diagram of a protection circuit for an electrochemical sensor provided by an embodiment of the present invention. The protection circuit is suitable for preventing voltage accumulation between positive and negative electrodes of an electrochemical sensor by short-circuiting the positive and negative electrodes when the electrochemical sensor is overloaded. Figure 1 As shown, the electrochemical sensor protection circuit includes:

[0039] The signal amplification module 101 includes an operational amplifier connected to the positive electrode of the electrochemical sensor and used to amplify the output signal of the electrochemical sensor to obtain an output voltage;

[0040] A reference voltage generating module 102, configured to generate a reference voltage according to a supply voltage of a system power supply and a maximum output voltage of the signal amplifying module 101, wherein the reference voltage does not exceed the maximum output voltage;

[0041] A voltage comparison module 103, the input end of the voltage comparison module 103 is respectively connected to the output end of the signal amplification module 101 and the reference voltage generation module 102, and is used for comparing the output voltage with the reference voltage in real time;

[0042] The protection switch module 104 is connected in parallel between the positive and negative electrodes of the electrochemical sensor and connected to the output end of the voltage comparison module 103, and is used to be turned on when the output voltage is greater than or equal to the reference voltage to short-circuit the positive and negative electrodes of the electrochemical sensor.

[0043] It should be noted that electrochemical sensors are generally divided into two types: current type and potential type. Current type sensors generate a current signal proportional to the concentration of the target substance through an electrochemical reaction, while the potential type measures the potential difference between electrodes. The technical solution of the present application is mainly applied to current type electrochemical sensors. Therefore, the signal amplification module 101 amplifies the output signal of the electrochemical sensor, that is, amplifies the current signal output by the electrochemical sensor.

[0044] In addition, it should be noted that the output signal of the signal amplification module 101 is a voltage signal, which means that the signal amplification module 101 realizes the conversion of current signal to voltage signal. Therefore, the signal amplification function of the signal amplification module 101 in the present application is not a narrow sense of amplifying a small current signal into a large current signal, but can also be a conversion of a weak (small) current signal into a measurable (large) voltage signal.

[0045] It can be understood that operational amplifiers are usually used in sensor signal conditioning circuits to achieve signal amplification. An operational amplifier that can convert a weak (small) current signal into a measurable (large) voltage signal can be a transimpedance amplifier. If the voltage signal output by the transimpedance amplifier needs to be further amplified, a voltage amplifier, such as an inverting voltage amplifier, can be cascaded after the transimpedance amplifier to achieve two-stage signal conditioning: current → voltage → voltage amplification.

[0046] If the inverting voltage amplifier is to be used alone, an input resistor needs to be added, so that the conversion of current signal to voltage signal can also be achieved.

[0047] Optionally, the signal amplification module 101 may be a transimpedance amplifier, or an inverting voltage amplifier with an input resistor, or a combination of the two.

[0048] It is understandable that no matter what kind of operational amplifier is used in the signal amplification module 101, saturation or even imbalance may occur when the electrochemical sensor outputs a very large current. Therefore, the technical solution of the present application provides a real-time monitoring of the output voltage of the signal amplification module 101, and when its output voltage is close to its maximum output voltage (i.e., saturation voltage), the protection switch module 104 is turned on, thereby achieving short-circuiting of the positive and negative electrodes of the electrochemical sensor, thereby achieving a solution to overload protection of the sensor.

[0049] In one embodiment, the operational amplifier used by the signal amplification module 101 is a rail-to-rail output operational amplifier, and its power supply can be determined according to the system power supply.

[0050] In a circuit system, depending on the power supply requirements of different devices, there may be only one system power supply, or multiple system power supplies, or there may be a reference system power supply and then multiple different power supplies may be differentiated based on the reference system power supply.

[0051] Optionally, the operational amplifier used in the signal amplification module 101 may be powered by a single power supply or a dual power supply.

[0052] It can be understood that, by using a rail-to-rail output operational amplifier, the output voltage can be close to the upper and lower limits of the operational amplifier power supply.

[0053] It should be noted that if the signal amplification module 101 adopts a multi-stage cascade of operational amplifiers, the output voltage of each stage of operational amplifiers needs to be monitored in real time. Since the monitoring method for each stage of operational amplifiers can refer to the monitoring method for a single-stage operational amplifier, this application focuses on the case where the signal amplification module 101 adopts a single-stage operational amplifier.

[0054] The function of the reference voltage generating module 102 is to provide a reference voltage close to the maximum output voltage of the signal amplifying module 101 , so as to serve as a comparison reference value for monitoring whether the output voltage of the signal amplifying module 101 is close to saturation.

[0055] There are many ways to generate a reference voltage, for example, including but not limited to the following methods: 1) Voltage divider network method: extracting the intermediate voltage from the power supply voltage as a reference through resistor voltage divider; 2) Zener diode method: using the reverse breakdown characteristics of the Zener diode to generate a stable voltage; 3) Bandgap reference circuit method: combining the temperature characteristics of bipolar transistors to achieve high-precision voltage reference; 4) Operational amplifier feedback method: building a feedback loop through an operational amplifier to improve the stability and driving capability of the reference voltage; 5) Application-specific integrated circuit reference source method: an integrated high-precision reference source that provides a standardized voltage output.

[0056] It is understandable that the system power supply is used as the power supply source of the entire circuit system and also as the power supply source of the reference voltage generation module 102, that is, the reference voltage generation module 102 processes the power supply voltage of the system power supply and converts it into a voltage close to the maximum output voltage of the signal amplification module 101, that is, the reference voltage. The maximum output voltage of the signal amplification module 101 depends on the selection of the operational amplifier. After the selection is determined, the corresponding maximum output voltage is a clear parameter.

[0057] Optionally, the reference voltage can be set to 80%-95% of the maximum output voltage.

[0058] In one embodiment, the reference voltage generating module includes a first resistor R1 and a second resistor R2, one end of R1 is connected to a system power supply, and the other end of R1 is grounded through R2; the resistance ratio of R1 to R2 ranges from 1:4 to 1:9.

[0059] The function of the voltage comparison module 103 is to obtain the output voltage of the signal amplification module 101 in real time, compare it with the reference voltage provided by the reference voltage generation module 102, and finally output an output signal indicating the comparison result.

[0060] There are many ways to compare two voltages and obtain the comparison results, including but not limited to the following methods: 1) Voltage comparator method: The voltage comparator is a core circuit element specifically used to compare two voltages. Its output is a high level or a low level, indicating the comparison result; 2) Analog circuit comparison method: For example, the voltage comparison is realized by using analog circuits such as difference comparison, ratio comparison, and bridge comparison; 3) Digital processing comparison method: For example, the voltage comparison is realized by combining an analog-to-digital converter and a microcontroller, or a digital comparator chip is used to realize voltage comparison.

[0061] In one embodiment, the voltage comparison module 103 implements voltage comparison using a comparator, including but not limited to a basic voltage comparator, a hysteresis comparator, and a window comparator.

[0062] In one embodiment, the voltage comparison module 103 uses a push-pull output comparator, and the power supply of the comparator is determined based on the system power supply; the non-inverting input terminal of the comparator is connected to the voltage dividing node of R1 and R2 in the reference voltage generation module 102, the inverting input terminal of the comparator is connected to the output terminal of the signal amplification module 101, and the output terminal of the comparator is connected to the protection switch module 104.

[0063] Optionally, the comparator used by the voltage comparison module 103 may be powered by a single power supply or a dual power supply.

[0064] It can be understood that the push-pull output comparator can actively output high and low levels without external pull-up resistors.

[0065] The function of the protection switch module 104 is to act as a switch device with a low-resistance short-circuit characteristic, which is arranged in parallel between the positive and negative electrodes of the electrochemical sensor, and then switched on and off according to the comparison result output by the voltage comparison module 103. When the output voltage of the signal amplification module 101 is greater than or equal to the reference voltage, it means that the output voltage of the signal amplification module 101 is close to its maximum output voltage (i.e., saturation voltage), and may continue to increase and exceed its maximum output voltage, thereby causing the operational amplifier to be saturated or even out of adjustment. At this time, the protection switch module 104 is turned on, thereby forming a low-resistance path to short-circuit the positive and negative electrodes of the electrochemical sensor, thereby avoiding the phenomenon of voltage accumulation between the positive and negative electrodes of the electrochemical sensor after the operational amplifier is saturated and out of adjustment, thereby realizing overload protection for the electrochemical sensor.

[0066] There are many options for switching devices with low-resistance short-circuit characteristics, such as but not limited to the following types: MOSFET drive network, junction field-effect transistor (Junction Field-Effect Transistor, JFET) drive network, insulated-gate bipolar transistor (Insulate-Gate Bipolar Transistor-IGBT) drive network.

[0067] In one embodiment, the protection switch module 104 includes a depletion-type PMOS transistor Q1 , a drain of Q1 connected to the positive electrode of the electrochemical sensor, a source of Q1 connected to the negative electrode of the electrochemical sensor, and a gate of Q1 connected to the output end of the voltage comparison module 103 .

[0068] In one embodiment, the protection switch module 104 includes an enhanced PMOS transistor Q2 , the source of Q2 is connected to the positive electrode of the electrochemical sensor, the drain of Q2 is connected to the negative electrode of the electrochemical sensor, and the gate of Q2 is connected to the output end of the voltage comparison module 103 .

[0069] It should be noted that when using a MOS tube as the core device of the protection switch module 104, a MOS tube with extremely low reverse leakage current should be selected. Reverse leakage current refers to the tiny current that still exists between the drain and the source when the MOS tube is in the cut-off state. Its essence is the leakage current generated by the reverse biased drain-substrate PN junction (or source-substrate PN junction), and the additional current caused by other physical effects is superimposed. If the reverse leakage current of the selected MOS tube is large, even if the MOS tube is in the cut-off state, there will still be current passing between the drain and the source, which will cause the output current of the electrochemical sensor to be partially shunted, thereby affecting the accuracy of the measurement result. The selection of a MOS tube with extremely low reverse leakage current can ensure that when the MOS tube is cut off, almost no current passes between the drain and the source, thereby avoiding interference with the output current of the electrochemical sensor.

[0070] The electrochemical sensor protection circuit provided by the embodiment of the present invention amplifies the output signal of the electrochemical sensor through the signal amplification module, generates a reference voltage close to the maximum output voltage of the signal amplification module 101 through the reference voltage generation module, compares the real-time output voltage of the signal amplification module with the reference voltage generated by the reference voltage generation module through the voltage comparison module, and when the real-time output voltage of the signal amplification module is greater than or equal to the reference voltage, the positive and negative electrodes of the electrochemical sensor are short-circuited by turning on the protection switch module. The electrochemical sensor protection circuit provided by the embodiment of the present invention realizes real-time monitoring of the output voltage of the operational amplifier. When the output voltage of the operational amplifier is close to saturation or has reached saturation, the overload protection mechanism can be quickly triggered to short-circuit the electrochemical sensor, thereby avoiding the operational amplifier from being out of adjustment due to long-term saturation. In addition, through the overload protection mechanism, the voltage accumulation of the positive and negative electrodes of the electrochemical sensor is effectively avoided, thereby avoiding damage to the electrochemical sensor due to overload, thereby extending the service life of the electrochemical sensor.

[0071] For example, Figure 1a A structural example diagram of an electrochemical sensor protection circuit according to an embodiment of the present invention is given. Figure 1a As shown, the protection circuit includes: a transimpedance amplifier U1, a first resistor R1, a second resistor R2, a comparator U2, and a depletion-type PMOS tube Q1.

[0072] The inverting input of U1 is connected to the positive electrode (pin 2) of the electrochemical sensor SENSOR, the non-inverting input of U1 is connected to the negative electrode (pin 1) of SENSOR and the reference potential Vref, the output SIN of U1 is connected to the inverting input of U1 through the feedback resistor Rf, and the power supply of U1 is connected to the system power supply VCC and the reference ground GND respectively. One end of R1 is connected to VCC, and the other end of R1 is connected to GND through R2. The non-inverting input of U2 is connected to the voltage-dividing node of R1 and R2, the inverting input of U2 is connected to the output SIN of U1, and the power supply of U2 is connected to the system power supply VCC and the reference ground GND respectively. The drain of Q1 is connected to the positive electrode (pin 2) of SENSOR, the source of Q1 is connected to the negative electrode (pin 1) of SENSOR, and the gate of Q1 is connected to the output of U2.

[0073] The resistor network composed of R1 and R2 generates a reference voltage that does not exceed the maximum output voltage of U1 through voltage division. When the output voltage of U1 is less than the reference voltage, U2 outputs a high level, Q1 is cut off, and the electrochemical sensor works normally; when the output voltage of U1 is greater than the reference voltage, U2 outputs a low level, and Q1 is turned on.

[0074] It should be noted that for the depletion type PMOS tube Q1, the pinch-off voltage of Q1 is V OFF , then VCC, Vref and V OFFThe following relationship is satisfied:

[0075]

[0076] It can be understood that for a depletion-type PMOS tube, its pinch-off voltage V OFF is a positive value. When Q1 is turned off, its gate-source voltage U GS =VCC-Vref should satisfy U GS >V OFF , that is, VCC-Vref>V OFF ; When Q1 is turned on, its gate-source voltage U GS =0-Vref should satisfy U GS <V OFF , that is, 0-Vref<V OFF .

[0077] For example, Figure 1b A structural example diagram of another electrochemical sensor protection circuit according to an embodiment of the present invention is given. Figure 1b As shown, the protection circuit includes: a transimpedance amplifier U1, a first resistor R1, a second resistor R2, a comparator U2, and an enhanced PMOS tube Q2.

[0078] The inverting input of U1 is connected to the positive electrode (pin 2) of the electrochemical sensor SENSOR, the non-inverting input of U1 is connected to the negative electrode (pin 1) of SENSOR and the reference potential Vref, the output SIN of U1 is connected to the inverting input of U1 through the feedback resistor Rf, and the power supply of U1 is connected to the system power supply VCC and the reference ground GND respectively. One end of R1 is connected to VCC, and the other end of R1 is connected to GND through R2. The non-inverting input of U2 is connected to the voltage-dividing node of R1 and R2, the inverting input of U2 is connected to the output SIN of U1, and the power supply of U2 is connected to the system power supply VCC and the reference ground GND respectively. The source of Q2 is connected to the positive electrode (pin 2) of SENSOR, the drain of Q2 is connected to the negative electrode (pin 1) of SENSOR, and the gate of Q2 is connected to the output of U2.

[0079] The resistor network composed of R1 and R2 generates a reference voltage that does not exceed the maximum output voltage of U1 through voltage division. When the output voltage of U1 is less than the reference voltage, U2 outputs a high level, Q2 is cut off, and the electrochemical sensor works normally; when the output voltage of U1 is greater than the reference voltage, U2 outputs a low level, and Q2 is turned on.

[0080] It should be noted that for the enhancement mode PMOS tube Q2, the threshold voltage of Q2 is V th , the constant potential difference between the positive and negative electrodes of the sensor is ΔV, then VCC, Vref, ΔV and V th The following relationship is satisfied:

[0081]

[0082] It can be understood that for an enhancement-mode PMOS transistor, its threshold voltage Vth is a negative value. When Q2 is turned off, its gate-source voltage U GS =VCC-(Vref+ΔV) should satisfy U GS >V th , that is, VCC-(Vref+ΔV)>V th ; When Q2 is turned on, its gate-source voltage U GS =0-(Vref+ΔV) should satisfy U GS <V th , that is, 0-(Vref+ΔV) <V th .

[0083] Figure 2 An embodiment of the present invention provides an electrochemical sensor protection circuit, which is suitable for preventing voltage accumulation between positive and negative electrodes of an electrochemical sensor by short-circuiting the positive and negative electrodes when the electrochemical sensor is overloaded or powered off. Figure 1 On the basis of the protection circuit shown, a dynamic control module located between the output end of the voltage comparison module and the protection switch module is added, which is used to control the protection switch module to be turned on when the output voltage of the signal amplification module is greater than or equal to the reference voltage, or when the system power supply is powered off, so as to short-circuit the positive and negative electrodes of the electrochemical sensor.

[0084] like Figure 2 As shown, the protection circuit includes: a signal amplification module 201 , a reference voltage generation module 202 , a voltage comparison module 203 , a dynamic control module 204 and a protection switch module 205 .

[0085] Understandably, Figure 1 The output end of the voltage comparison module in the protection circuit shown is directly connected to the protection switch module. Figure 1a and Figure 1b Take the circuit shown in the figure as an example. When the system power is off, the output of comparator U2 is in a high impedance state. Its voltage is determined by parasitic capacitance or leakage current of external circuits. There may be an uncertain level left. As a result, Q1 may not be able to conduct reliably due to the gate being suspended. Figure 1 The solution shown cannot guarantee that the protection switch module can be reliably turned on when the system power fails, and thus cannot guarantee that the power failure protection of the electrochemical sensor can be achieved.

[0086] To achieve power-off protection for the electrochemical sensor, it is necessary to ensure that the protection switch module 205 can be turned on when the system power is off to short-circuit the positive and negative electrodes of the electrochemical sensor. Therefore, the power off of the system power can be used as a sufficient condition for the protection switch module 205 to be turned on. In addition, the purpose of this embodiment is to achieve protection of the electrochemical sensor under two working conditions: overload and system power off, based on the aforementioned embodiment. Therefore, while adding the dynamic control module 204 to achieve the power-off protection effect, it is also necessary to ensure that the overload protection effect is not affected.

[0087] In one embodiment, the dynamic control module 204 includes a third resistor R3 and a fourth resistor R4, one end of R3 is connected to the system power supply, the other end of R3 is connected to the output end of the voltage comparison module 203 through R4, and the common node of R3 and R4 is connected to the protection switch module 205.

[0088] Optionally, R3 and R4 have equal resistance values, and the resistance range is 1 kΩ to 10 kΩ.

[0089] The electrochemical sensor protection circuit provided by the embodiment of the present invention amplifies the output signal of the electrochemical sensor through the signal amplification module, generates a reference voltage close to the maximum output voltage of the signal amplification module through the reference voltage generation module, compares the real-time output voltage of the signal amplification module with the reference voltage generated by the reference voltage generation module through the voltage comparison module, and when the real-time output voltage of the signal amplification module is greater than or equal to the reference voltage, or when the system power is powered off, the protection switch module is controlled by the dynamic control module to conduct to achieve the short circuit of the positive and negative electrodes of the electrochemical sensor. The electrochemical sensor protection circuit provided by the embodiment of the present invention realizes real-time monitoring of the output voltage of the operational amplifier. When the output voltage of the operational amplifier is close to saturation or has reached saturation, the overload protection mechanism can be quickly triggered to short-circuit the electrochemical sensor, thereby avoiding the operational amplifier from being out of adjustment due to long-term saturation. In addition, through the overload protection mechanism, the positive and negative electrodes of the electrochemical sensor are effectively prevented from accumulating voltage, thereby avoiding damage to the electrochemical sensor due to overload, thereby extending the service life of the electrochemical sensor. In addition, when the system is powered off, the power-off protection mechanism can be triggered to short-circuit the electrochemical sensor to ensure that the positive and negative electrodes of the electrochemical sensor do not accumulate voltage. Therefore, the embodiment of the present invention can protect the electrochemical sensor in both overload and power-off conditions by short-circuiting the positive and negative electrodes.

[0090] For example, Figure 2a A structural example diagram of an electrochemical sensor protection circuit according to an embodiment of the present invention is given. Figure 2a As shown, the protection circuit includes: a transimpedance amplifier U1, a first resistor R1, a second resistor R2, a comparator U2, a depletion-type PMOS tube Q1, a third resistor R3, and a fourth resistor R4.

[0091] The inverting input of U1 is connected to the positive electrode (pin 2) of the electrochemical sensor SENSOR, the non-inverting input of U1 is connected to the negative electrode (pin 1) of SENSOR and the reference potential Vref, the output SIN of U1 is connected to the inverting input of U1 through the feedback resistor Rf, and the power supply of U1 is connected to the system power supply VCC and the reference ground GND respectively. One end of R1 is connected to VCC, and the other end of R1 is connected to GND through R2. The non-inverting input of U2 is connected to the voltage-dividing node of R1 and R2, the inverting input of U2 is connected to the output SIN of U1, and the power supply of U2 is connected to the system power supply VCC and the reference ground GND respectively. One end of R3 is connected to VCC, and the other end of R3 is connected to the output of U2 through R4. The drain of Q1 is connected to the positive electrode (pin 2) of SENSOR, the source of Q1 is connected to the negative electrode (pin 1) of SENSOR, and the gate of Q1 is connected to the common node of R3 and R4.

[0092] The resistor network composed of R1 and R2 generates a reference voltage that does not exceed the maximum output voltage of U1 through voltage division. When the output voltage of U1 is less than the reference voltage, U2 outputs a high level, Q1 is cut off, and the electrochemical sensor works normally; when the output voltage of U1 is greater than the reference voltage, U2 outputs a low level, and Q1 is turned on; when the system power is off, one end of R3 connected to VCC is equivalent to grounding, and Q1 is turned on.

[0093] It should be noted that for the depletion type PMOS tube Q1, the pinch-off voltage of Q1 is V OFF , then VCC, Vref and V OFF The following relationship is satisfied:

[0094]

[0095] It can be understood that during the normal measurement of the electrochemical sensor, the comparator U2 outputs a high level and is transmitted to the gate of Q1 through R4. At the same time, R3 acts as a pull-up resistor to pull the gate voltage of Q1 up to the system power supply voltage VCC. The two together ensure that the gate voltage of Q1 remains at a high level. When the current output by the electrochemical sensor is too large, causing the output voltage of the op amp U1 to approach saturation, the comparator U2 outputs a low level. At this time, R3 and R4 form a voltage divider, and the gate voltage of Q1 is In addition, R3 also protects Q1, that is, it prevents the gate of Q1 from floating and avoids unstable state caused by external interference. When the system power is off, the end of R3 connected to VCC is equivalent to grounding, the output end of U2 is in high impedance state, and R5 has no effective current path. At this time, R3 provides a low impedance path to the ground for the gate of Q1. R3 is equivalent to a pull-down resistor, pulling the gate voltage of Q1 down to 0V.

[0096] For a depletion-type PMOS tube, its pinch-off voltage V OFF is a positive value. When Q1 is turned off, its gate-source voltage U GS =VCC-Vref should satisfy U GS >V OFF , that is, VCC-Vref>V OFF ; When Q1 is turned on in the case of power failure, its gate-source voltage U GS =0-Vref should satisfy U GS <V OFF , that is, 0-Vref<V OFF ; When Q1 is turned on under overload conditions, its gate-source voltage Should satisfy U GS <V OFF ,Right now

[0097] When R3=R4 and the resistance range is 1kΩ~10kΩ, it can take into account both system power consumption and response speed. At this time, formula (3) is converted into:

[0098]

[0099] For example, Figure 2b A structural example diagram of an electrochemical sensor protection circuit according to an embodiment of the present invention is given. Figure 2b As shown, the protection circuit includes: a transimpedance amplifier U1, a first resistor R1, a second resistor R2, a comparator U2, an enhanced PMOS transistor Q2, a third resistor R3, and a fourth resistor R4.

[0100] The inverting input of U1 is connected to the positive electrode (pin 2) of the electrochemical sensor SENSOR, the non-inverting input of U1 is connected to the negative electrode (pin 1) of SENSOR and the reference potential Vref, the output SIN of U1 is connected to the inverting input of U1 through the feedback resistor Rf, and the power supply of U1 is connected to the system power supply VCC and the reference ground GND respectively. One end of R1 is connected to VCC, and the other end of R1 is connected to GND through R2. The non-inverting input of U2 is connected to the voltage-dividing node of R1 and R2, the inverting input of U2 is connected to the output SIN of U1, and the power supply of U2 is connected to the system power supply VCC and the reference ground GND respectively. One end of R3 is connected to VCC, and the other end of R3 is connected to the output of U2 through R4. The source of Q2 is connected to the positive electrode (pin 2) of SENSOR, the drain of Q2 is connected to the negative electrode (pin 1) of SENSOR, and the gate of Q2 is connected to the common node of R3 and R4.

[0101] The resistor network composed of R1 and R2 generates a reference voltage that does not exceed the maximum output voltage of U1 through voltage division. When the output voltage of U1 is less than the reference voltage, U2 outputs a high level, Q2 is cut off, and the electrochemical sensor works normally; when the output voltage of U1 is greater than the reference voltage, U2 outputs a low level, Q2 is turned on; when the system power is off, one end of R3 connected to VCC is equivalent to grounding, and Q2 is turned on.

[0102] It should be noted that for the enhancement mode PMOS tube Q2, the threshold voltage of Q2 is V th , the constant potential difference between the positive and negative electrodes of the sensor is ΔV, then VCC, Vref, ΔV and V th The following relationship is satisfied:

[0103]

[0104] It can be understood that for an enhancement mode PMOS tube, its threshold voltage V th is a negative value. When Q2 is turned off, its gate-source voltage U GS =VCC-(Vref+ΔV) should satisfy U GS >V th , that is, VCC-(Vref+ΔV)>V th ; When Q2 is turned on in the case of power failure, its gate-source voltage U GS =0-(Vref+ΔV) should satisfy U GS <V th , that is, 0-(Vref+ΔV) <V th ; When Q1 is turned on under overload conditions, its gate-source voltage Should satisfy U GS <V th ,Right now

[0105] When R3=R4 and the resistance range is 1kΩ~10kΩ, it can take into account both system power consumption and response speed. At this time, formula (5) is transformed into:

[0106]

[0107] It is worth noting that in the above-mentioned embodiment of the electrochemical sensor protection circuit, the modules included are only divided according to functional logic, but are not limited to the above-mentioned division, as long as the corresponding functions can be realized; in addition, the specific names of the functional units are only for the convenience of distinguishing each other, and are not used to limit the protection scope of the present invention.

[0108] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. An electrochemical sensor protection circuit, characterized in that: include: A signal amplification module, including an operational amplifier, connected to the positive electrode of the electrochemical sensor, and used to amplify the output signal of the electrochemical sensor to obtain an output voltage; A reference voltage generating module, used for generating a reference voltage according to a supply voltage of a system power supply and a maximum output voltage of the signal amplifying module, wherein the reference voltage does not exceed the maximum output voltage; A voltage comparison module, the input end of which is respectively connected to the output end of the signal amplification module and the reference voltage generation module, for comparing the output voltage with the reference voltage in real time; The protection switch module is connected in parallel between the positive and negative electrodes of the electrochemical sensor and connected to the output end of the voltage comparison module, and is used to be turned on when the output voltage is greater than or equal to the reference voltage to short-circuit the positive and negative electrodes of the electrochemical sensor.

2. The electrochemical sensor protection circuit according to claim 1, characterized in that: The operational amplifier is a rail-to-rail output operational amplifier, and a power supply of the operational amplifier is determined based on the system power supply.

3. The electrochemical sensor protection circuit according to claim 1 or 2, characterized in that: The reference voltage generating module comprises a first resistor R1 and a second resistor R2, one end of the R1 is connected to the system power supply, and the other end of the R1 is grounded through the R2; The resistance ratio of the R1 to the R2 ranges from 1:4 to 1:

9.

4. The electrochemical sensor protection circuit according to claim 3, characterized in that: The voltage comparison module includes a push-pull output comparator, and the power supply of the comparator is determined based on the system power supply; The non-inverting input terminal of the comparator is connected to the voltage-dividing node of R1 and R2, the inverting input terminal of the comparator is connected to the output terminal of the signal amplification module, and the output terminal of the comparator is connected to the protection switch module.

5. The electrochemical sensor protection circuit according to any one of claims 1 to 4, characterized in that: The protection switch module includes a depletion-type PMOS tube Q1; The drain of Q1 is connected to the positive electrode of the electrochemical sensor, the source of Q1 is connected to the negative electrode of the electrochemical sensor, and the gate of Q1 is connected to the output end of the voltage comparison module.

6. The electrochemical sensor protection circuit according to claim 5, characterized in that: The negative electrode of the electrochemical sensor is connected to a reference potential Vref; The supply voltage of the system power supply is VCC, and the pinch-off voltage of Q1 is V OFF , then VCC, Vref and V OFF The following relationship is satisfied:

7. The electrochemical sensor protection circuit according to claim 6, characterized in that: The protection switch module includes an enhanced PMOS tube Q2; The source of Q2 is connected to the positive electrode of the electrochemical sensor, the drain of Q2 is connected to the negative electrode of the electrochemical sensor, and the gate of Q2 is connected to the output end of the voltage comparison module.

8. The electrochemical sensor protection circuit according to claim 7, characterized in that: The negative electrode of the electrochemical sensor is connected to a reference potential Vref; The supply voltage of the system power supply is VCC, and the threshold voltage of Q2 is V th , the constant potential difference between the positive and negative electrodes of the sensor is ΔV, then VCC, Vref, ΔV and V th The following relationship is satisfied:

9. The electrochemical sensor protection circuit according to any one of claims 1 to 8, characterized in that: A dynamic control module is also provided between the output end of the voltage comparison module and the protection switch module, for controlling the protection switch module to conduct when the output voltage of the signal amplification module is greater than or equal to the reference voltage, or when the system power supply fails, so as to short-circuit the positive and negative electrodes of the electrochemical sensor.

10. The electrochemical sensor protection circuit according to claim 9, characterized in that: The dynamic control module includes a third resistor R3 and a fourth resistor R4, one end of R3 is connected to the system power supply, the other end of R3 is connected to the output end of the voltage comparison module through R4, and a common node of R3 and R4 is connected to the protection switch module.

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