A capacitive inductive sensing circuit

Abstract

This utility model relates to the field of capacitive sensors, specifically disclosing a capacitive sensing circuit. The circuit includes a temperature compensation module, a signal processing module, a capacitive sensing module, and a power supply and output module. The temperature compensation module includes an operational amplifier U1, a temperature sensor RT, and a voltage divider resistor R3. The temperature sensor RT is patch-connected to the capacitive sensor. The temperature sensor RT converts the temperature change of the capacitive sensor into a voltage signal output connected to the operational amplifier U1. The operational amplifier U1 outputs a temperature compensation voltage Vt to the signal processing module. The signal processing module includes a chopper-stabilized operational amplifier U2 and a bistable trigger U3, which are electrically connected. The capacitive sensing module includes capacitors C1 and C2. The common connection point of capacitors C1 and C2 leads to a signal output terminal OUT, which is externally connected to a low-pass filter. Simultaneously, the signal output terminal OUT of capacitors C1 and C2 is electrically connected to the inverting input of the chopper-stabilized operational amplifier U2.

Description

Technical Field

[0001] This utility model relates to the field of capacitive sensors, specifically a capacitive sensing circuit. Background Technology

[0002] Capacitive sensing technology is widely used in consumer electronics, industrial automation, and other fields due to its advantages such as non-contact detection, fast response, and long lifespan. Its core is to convert non-electrical quantity changes into capacitance fluctuations, and then into electrical signals for detection. However, existing circuits have significant technical bottlenecks and cannot meet the requirements for high precision.

[0003] First, temperature interference is a prominent issue. The capacitance of capacitive sensing elements (such as humidity-sensitive capacitors) is sensitive to temperature, and fluctuations in ambient temperature can easily cause "temperature drift." Some circuits lack a dedicated compensation mechanism or only use a coarse compensation method, which cannot dynamically offset temperature drift across the entire operating temperature range, resulting in a significant decrease in detection accuracy.

[0004] Second, the processing of weak signals and the ability to resist interference are insufficient. The capacitance of the sensing capacitor changes very little, resulting in a weak electrical signal. Existing circuits mostly use ordinary operational amplifiers, which have large offset voltage and temperature drift, easily leading to signal distortion. Furthermore, there is a lack of efficient closed-loop control combined with temperature compensation. Bistable triggers are easily interfered with, resulting in poor output signal stability. External filtering schemes are simple, resulting in a low signal-to-noise ratio.

[0005] As various fields demand higher sensing accuracy and environmental adaptability, existing circuits can no longer meet the requirements. Developing capacitive sensing circuits that can accurately resist temperature drift and efficiently process weak signals has become an urgent problem to be solved. Utility Model Content

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a capacitive sensing circuit to solve the problems mentioned in the background art.

[0007] This utility model provides a capacitive sensing circuit, including a temperature compensation module, a signal processing module, a capacitive sensing module, and a power supply and output module. The temperature compensation module includes an operational amplifier U1, a temperature sensor RT, and a voltage divider resistor R3. The temperature sensor RT is surface-mount connected to the capacitive sensor. The temperature sensor RT converts the temperature change of the capacitive sensor into a voltage signal output connected to the operational amplifier U1. The output terminal of the operational amplifier U1 outputs a temperature compensation voltage Vt to the signal processing module. The signal processing module includes a chopper-stabilized operational amplifier U2 and a bistable trigger U3 electrically connected. The capacitive sensing module includes capacitors C1 and C2. The common connection point of capacitors C1 and C2 leads to a signal output terminal OUT. The signal output terminal OUT is externally connected to a low-pass filter. At the same time, the signal output terminal OUT of capacitors C1 and C2 is electrically connected to the inverting input of the chopper-stabilized operational amplifier U2.

[0008] Furthermore, one end of the temperature sensor RT is connected to the positive terminal VIN of the power supply, and the other end of the temperature sensor RT is connected to the non-inverting input of the operational amplifier U1 via the voltage divider resistor R3. The inverting input of the operational amplifier U1 is connected to an external reference source to provide a stable reference voltage, and the output terminal of the operational amplifier U1 outputs a temperature compensation voltage Vt.

[0009] Furthermore, one end of the chopper-stabilized operational amplifier U2 is connected to the positive power supply VIN after filtering. The filtering at one end of the chopper-stabilized operational amplifier U2 includes a diode D3 and a capacitor C3 that are electrically connected to the positive power supply VIN.

[0010] Furthermore, the non-inverting input of the chopper-stabilized zero-state op-amp U2 is connected to the reference voltage source Vr, and the inverting input of the chopper-stabilized zero-state op-amp U2 is connected to the temperature compensation voltage Vt output by the temperature compensation module and the feedback signal from the capacitor sensing module; the output of the chopper-stabilized zero-state op-amp U2 is connected to the bistable trigger U3.

[0011] Furthermore, the reset terminal R and set terminal S of the bistable trigger U3 are electrically connected to the output terminal of the chopper-stabilized operational amplifier U2, and the output terminal of the bistable trigger U3 is electrically connected to the capacitance sensing module.

[0012] Furthermore, the capacitive sensing module includes diodes D1 and D2, capacitors C1 and C2, resistors R1 and R2, and a signal output terminal OUT. Resistor R1 is connected in parallel with diode D2. One end of the parallel connection between resistor R1 and diode D2 is electrically connected to one output terminal of U3, and the other end is electrically connected to capacitor C1. Resistor R2 is connected in parallel with diode D1. One end of the parallel connection between resistor R2 and diode D1 is electrically connected to the other output terminal of U3, and the other end is electrically connected to capacitor C2. Capacitors C1 and C2 are electrically connected to the signal output terminal OUT. Capacitors C1 and C2 are also electrically connected to the inverting input terminal of the chopper-stabilized operational amplifier U2. An external low-pass filter is connected to the signal output terminal OUT.

[0013] The beneficial effects of this utility model are:

[0014] This application achieves high precision and high stability of capacitive sensing through the synergistic effect of temperature compensation and signal closed-loop control.

[0015] Specifically, in the temperature compensation module, the temperature sensor RT is tightly connected to the capacitor sensor patch, which can capture the temperature change of the capacitor sensor in real time and convert it into a voltage signal. After being processed by the operational amplifier U1, the temperature compensation voltage Vt is output, which can accurately offset the capacitance drift caused by temperature fluctuations in the capacitor sensor module, thus eliminating the influence of temperature on the detection accuracy from the source.

[0016] Simultaneously, the signal processing module and the capacitance sensing module form a closed-loop control. The chopper-stabilized operational amplifier U2 precisely processes the temperature compensation voltage Vt and the feedback signal from the capacitance sensing module, driving the bistable trigger U3 to control the charging and discharging sequence of capacitors C1 and C2. The voltage change signal generated by the capacitor charging and discharging is then fed back to the inverting input of U2, achieving dynamic signal correction. This dual closed-loop control mechanism effectively suppresses the effects of the circuit's own offset voltage, temperature drift, and external interference, ensuring that the capacitance sensing module can stably convert non-electrical quantity changes into accurate electrical signals. Ultimately, this enables the circuit to maintain high-precision sensing performance under different temperature environments. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of a capacitive induction sensing circuit according to the present invention. Detailed Implementation

[0018] This utility model discloses a capacitive induction sensing circuit, such as Figure 1 As shown, the system includes a temperature compensation module, a signal processing module, a capacitance sensing module, and a power supply and output module. The temperature compensation module includes an operational amplifier U1, a temperature sensor RT, and a voltage divider resistor R3. The temperature sensor RT is surface-mount connected to the capacitance sensor. The temperature sensor RT converts the temperature change of the capacitance sensor into a voltage signal output connected to the operational amplifier U1. The operational amplifier U1 outputs a temperature compensation voltage Vt to the signal processing module. The signal processing module includes a chopper-stabilized operational amplifier U2 and a bistable trigger U3 that are electrically connected. The capacitance sensing module includes capacitors C1 and C2. The common connection point of capacitors C1 and C2 leads to a signal output terminal OUT. The signal output terminal OUT is externally connected to a low-pass filter. At the same time, the signal output terminal OUT of capacitors C1 and C2 is electrically connected to the inverting input of the chopper-stabilized operational amplifier U2.

[0019] The capacitive sensing circuit includes a temperature compensation module, a signal processing module, a capacitive sensing module, and a power supply and output module. In the temperature compensation module, operational amplifier U1, a temperature sensor (RT), and voltage divider resistor R3 work together. The temperature sensor (RT) and the capacitive sensor are tightly connected via surface mount technology, accurately capturing temperature changes from the capacitive sensor and converting these changes into a voltage signal, which is then transmitted to operational amplifier U1. The non-inverting input of operational amplifier U1 receives the voltage signal from the temperature sensor (RT) via voltage divider resistor R3, while the inverting input is connected to an external reference source to obtain a stable reference voltage. After processing, the output terminal outputs a temperature compensation voltage Vt, which is then transmitted to the signal processing module. In the signal processing module, a chopper-stabilized operational amplifier U2 and a bistable trigger U3 are electrically connected. The non-inverting input of the chopper-stabilized operational amplifier U2 is connected to a reference voltage source Vr, while the inverting input simultaneously receives the temperature compensation voltage Vt output from the temperature compensation module and the signal feedback from the capacitive sensing module. After internal processing, the output terminal is connected to the bistable trigger U3. The capacitance sensing module is centered around capacitors C1 and C2. Their common connection point leads to the signal output terminal OUT. This output terminal is connected to an external low-pass filter to filter high-frequency interference in the signal. At the same time, the signal output terminal OUT is electrically connected to the inverting input of the chopper-stabilized zero-voltage operational amplifier U2, which provides real-time feedback on the voltage changes generated by the charging and discharging of the capacitors. This allows the chopper-stabilized zero-voltage operational amplifier U2 to dynamically adjust its output based on the capacitor state, ensuring the stability of the drive for the bistable trigger U3. All modules work together to complete the capacitance sensing function.

[0020] In a preferred embodiment, one end of the temperature sensor RT is connected to the positive terminal VIN of the power supply, and the other end of the temperature sensor RT is connected to the non-inverting input of the operational amplifier U1 via the voltage divider resistor R3. The inverting input of the operational amplifier U1 is connected to an external reference source to provide a stable reference voltage, and the output terminal of the operational amplifier U1 outputs a temperature compensation voltage Vt.

[0021] One end of the temperature sensor (RT) is directly connected to the positive terminal of the power supply (VIN) to obtain the electrical energy required for operation. The other end is connected in series with a voltage divider resistor R3, which limits the current and distributes the voltage. After passing through the voltage divider resistor R3, it is connected to the non-inverting input of operational amplifier U1, transmitting the temperature-converted voltage signal to operational amplifier U1. An independent reference source is connected to the inverting input of operational amplifier U1. This reference source provides a stable and constant reference voltage, allowing operational amplifier U1 to have a precise comparison reference. Internally, operational amplifier U1 processes the temperature voltage signal input at the non-inverting input and the reference voltage at the inverting input, finally outputting a temperature compensation voltage Vt from its output terminal for subsequent signal conditioning, ensuring stable operation of the circuit under different temperatures.

[0022] In a preferred embodiment, one end of the chopper-stabilized operational amplifier U2 is connected to the positive power supply VIN after filtering. The filtering at one end of the chopper-stabilized operational amplifier U2 includes a diode D3 and a capacitor C3 electrically connected to the positive power supply VIN.

[0023] The power input of the chopper-stabilized operational amplifier U2 is first processed by a filter circuit composed of diode (D3) and capacitor (C3) before being electrically connected to the positive power supply (VIN). This provides a stable and interference-free operating power supply for the chopper-stabilized operational amplifier U2. Specifically, the anode of diode (D3) is directly connected to the positive power supply (VIN), while the cathode of diode (D3) is electrically connected to one end of capacitor (C3) and directly connected to the power input of chopper-stabilized operational amplifier U2. Diode (D3) acts as a unidirectional conductor, effectively preventing damage to chopper-stabilized operational amplifier U2 from reverse voltage surges at the positive power supply (VIN), thus providing reverse protection. Capacitor (C3) quickly absorbs high-frequency noise and voltage ripple in the power supply, keeping the power supply voltage input to chopper-stabilized operational amplifier U2 stable. This prevents power fluctuations from interfering with the accuracy of chopper-stabilized operational amplifier U2's processing of the temperature compensation voltage Vt and the feedback signal from the capacitor sensing module, ensuring a stable output trigger signal to drive the bistable trigger U3.

[0024] In a preferred embodiment, the non-inverting input of the chopper-stabilized operational amplifier U2 is connected to a reference voltage source Vr, the inverting input of the chopper-stabilized operational amplifier U2 is connected to the temperature compensation voltage Vt output by the temperature compensation module and the feedback signal from the capacitance sensing module, and the output of the chopper-stabilized operational amplifier U2 is connected to a bistable trigger U3.

[0025] The non-inverting input of the chopper-stabilized operational amplifier U2 is directly connected to the reference voltage source Vr, which provides a stable reference level for signal processing. The inverting input of U2 is connected to two signals: a temperature compensation voltage Vt from the temperature compensation module and a signal fed back from the capacitance sensing module. These two signals are superimposed at the inverting input. Through its internal high-frequency chopping technology, the chopper-stabilized operational amplifier U2 effectively suppresses its offset voltage and temperature drift. After accurately amplifying and processing the signal superimposed at the inverting input, it outputs a corresponding level signal. This output is directly connected to the bistable trigger U3, transmitting the processed signal to drive the bistable trigger U3 for state switching and control.

[0026] In a preferred embodiment, the reset terminal R and set terminal S of the bistable trigger U3 are electrically connected to the output terminal of the chopper-stabilized operational amplifier U2, and the output terminal of the bistable trigger U3 is electrically connected to the capacitance sensing module.

[0027] The bistable multivibrator U3 has two key control terminals: a reset terminal R and a set terminal S. Both terminals are directly electrically connected to the output of the chopper-stabilized zero-level operational amplifier U2, receiving the level signal output by the chopper-stabilized zero-level operational amplifier U2 after processing. When the level signal output by the chopper-stabilized zero-level operational amplifier U2 triggers the reset terminal R, the bistable multivibrator U3 switches to the reset state; when the same level signal triggers the set terminal S, the bistable multivibrator U3 switches to the set state, thus achieving precise state control. Simultaneously, the bistable multivibrator U3 also has two output terminals, which are electrically connected to the common parallel terminals of resistor R1 and diode D2, and resistor R2 and diode D1, respectively, in the capacitance sensing module. These output terminals transmit their own state signals to the capacitance sensing module, thereby controlling the charging and discharging sequence of capacitors C1 and C2 in the capacitance sensing module, ensuring that the capacitance sensing module can stably complete the conversion of non-electrical quantities into electrical signals.

[0028] In a preferred embodiment, the capacitance sensing module includes diodes D1 and D2, capacitors C1 and C2, resistors R1 and R2, and a signal output terminal OUT. Resistor R1 is connected in parallel with diode D2. One end of the parallel connection between resistor R1 and diode D2 is electrically connected to one output terminal of U3, and the other end is electrically connected to capacitor C1. Resistor R2 is connected in parallel with diode D1. One end of the parallel connection between resistor R2 and diode D1 is electrically connected to the other output terminal of U3, and the other end is electrically connected to capacitor C2. Capacitors C1 and C2 are electrically connected to the signal output terminal OUT. Capacitors C1 and C2 are also electrically connected to the inverting input terminal of the chopper-stabilized operational amplifier U2. An external low-pass filter is connected to the signal output terminal OUT.

[0029] The capacitive sensing module includes diodes D1 and D2, capacitors C1 and C2, resistors R1 and R2, and a signal output terminal OUT. Each component forms a symmetrical charging and discharging circuit according to functional requirements. Resistor R1 and diode D2 are connected in parallel. One end of their parallel common terminal is directly connected to one output terminal of the bistable trigger U3 to receive the state control signal output by the trigger; the other end is connected to one end of capacitor C1, providing a charging and discharging path for capacitor C1. Similarly, resistor R2 and diode D1 are also connected in parallel. One end of their parallel common terminal is connected to the other output terminal of the bistable trigger U3, and the other end is connected to one end of capacitor C2, forming a charging and discharging circuit for capacitor C2. The other ends of capacitors C1 and C2 converge and are connected together to the signal output terminal OUT. Simultaneously, the ends of capacitors C1 and C2 closest to the signal output terminal OUT are also electrically connected to the inverting input terminal of the chopper-stabilized operational amplifier U2 via wires. This allows the voltage change signal generated during capacitor charging and discharging to be fed back to U2 as a feedback signal, forming a closed-loop signal control. An external low-pass filter is connected to the signal output terminal OUT. This filter removes high-frequency interference noise mixed in with the capacitor charging and discharging signal, ensuring that the output electrical signal accurately reflects the non-electrical quantity changes (such as displacement, humidity, etc.) detected by the capacitor sensor, providing a stable and clean input signal for subsequent circuits.

[0030] The working principle of this application is as follows:

[0031] The positive terminal of the power supply (VIN) provides operating power to the entire capacitive sensing circuit. Part of it is directly supplied to one end of the temperature sensor (RT) of the temperature compensation module to power it; the other part is processed by a filter circuit composed of diode (D3) and capacitor (C3) and then supplied to the chopper-stabilized operational amplifier U2 of the signal processing module. The anode of diode (D3) is connected to the positive terminal of the power supply (VIN), and the cathode is connected to the power supply terminal of chopper-stabilized operational amplifier U2. The unidirectional conductivity is used to prevent reverse voltage surges from damaging chopper-stabilized operational amplifier U2. One end of capacitor (C3) is connected to the cathode of diode (D3), and the other end is grounded (GND). It can absorb high-frequency noise and voltage ripple in the power supply and ensure stable power supply to chopper-stabilized operational amplifier U2.

[0032] In the temperature compensation module, the temperature sensor (RT), which is closely connected to the capacitive sensor patch, changes its resistance value as the temperature of the capacitive sensor changes. Its other end is connected in series with a voltage divider resistor R3 and then connected to the non-inverting input of the operational amplifier U1, forming a voltage divider circuit that converts the temperature change into a voltage signal, which is then input to the non-inverting input of the operational amplifier U1. The inverting input of the operational amplifier U1 is connected to an external reference source to obtain a stable reference voltage. By comparing the temperature voltage signal at the non-inverting input with the reference voltage at the inverting input, the module performs calculations and outputs a temperature compensation voltage Vt. This voltage is transmitted to the inverting input of the chopper-stabilized operational amplifier U2 to compensate for the capacitance drift caused by temperature fluctuations in the capacitive sensing module, thus preventing temperature from affecting the detection accuracy.

[0033] In the signal processing module, the non-inverting input of the chopper-stabilized operational amplifier U2 is connected to the reference voltage source Vr to obtain a stable reference level, while the inverting input simultaneously receives the temperature compensation voltage Vt and the feedback signal from the capacitance sensing module. Through internal high-frequency chopping technology, the offset voltage and temperature drift are suppressed, and the superimposed signal is accurately amplified and processed. Then, a level signal is output from the output terminal to the reset terminal R and the set terminal S of the bistable trigger U3: when the level signal triggers the reset terminal R, the bistable trigger U3 switches to the reset state; when the set terminal S is triggered, it switches to the set state, realizing precise state control.

[0034] The two outputs of the bistable trigger U3 are connected to the common terminal of the parallel connection of resistor R1 and diode D2, and the common terminal of the parallel connection of resistor R2 and diode D1, respectively, in the capacitance sensing module. This transmits the status signal to the capacitance sensing module to control the charging and discharging sequence of capacitors C1 and C2. Specifically, the other end of the parallel connection of resistor R1 and diode D2 is connected to capacitor C1, and the other end of the parallel connection of resistor R2 and diode D1 is connected to capacitor C2. Diodes D1 and D2 control the direction of the charging and discharging current, resistors R1 and R2 limit the current magnitude, and capacitors C1 and C2, as core sensing elements, change their capacitance values ​​with the detected non-electrical quantities (such as displacement or humidity), resulting in changes in the charging and discharging voltage signal.

[0035] The other ends of capacitors C1 and C2 converge and are connected to the signal output terminal OUT. This output terminal is connected to an external low-pass filter to filter high-frequency interference noise and output a stable electrical signal that accurately reflects changes in non-electrical quantities for use by subsequent circuits. On the other hand, the voltage change signal generated by the charging and discharging of the capacitors is fed back as a feedback signal to the inverting input of the chopper stabilizing operational amplifier U2. This forms a double closed-loop control with the temperature compensation voltage Vt (the temperature compensation loop cancels temperature drift, and the signal feedback loop corrects deviation), ensuring the stability of the output signal of the chopper stabilizing operational amplifier U2 and guaranteeing the reliability of the bistable trigger U3 in controlling the capacitor sensing module. Ultimately, this achieves high-precision capacitive sensing of non-electrical quantities.

[0036] In one specific embodiment, this embodiment is adapted to humidity detection scenarios in the consumer electronics field, with an operating temperature range of 0℃ to 60℃, and the detection accuracy meets the needs of daily environmental humidity monitoring. It can be directly connected to home MCU control systems.

[0037] In the power supply and output module, the positive terminal VIN of the power supply is connected to a 5V USB power supply, and a low dropout linear regulator AMS1117-3.3 is connected in series. This regulator is in an SOT-223 package and outputs a stable 3.3V voltage to power the various modules of the circuit. The signal output terminal OUT is connected to an external low-pass filter to filter high-frequency interference in the humidity detection signal and ensure that the output signal is stably transmitted to the subsequent MCU (such as STM32F103C8T6).

[0038] The operational amplifier U1 of the temperature compensation module uses an MCP6004, which is an SOIC-14 packaged quad op-amp structure, powered by 3.3V, with a quiescent current of 500nA and an open-loop gain of 100dB, suitable for low-power requirements. The temperature sensor RT is an NTC thermistor in a 0603 surface mount package, model NCP15XH103J03RC, with a resistance of 10kΩ at 25℃ and a B value of 3950K. It is connected to the capacitive sensor surface mount via thermally conductive adhesive and attached to the surface of the capacitive sensor in the humidity detection area. The system captures changes in ambient temperature in real time. The voltage divider resistor R3 is a thick-film resistor in a 0603 package, model RC0603JR-0710KL, which is connected in series with RT to the non-inverting input of operational amplifier U1. The inverting input of operational amplifier U1 is connected to an external reference source ADR5040, which is in an SOT-23 package, outputs a stable 1.25V voltage, has an initial accuracy of ±0.1%, and a temperature drift of ±10ppm / ℃, providing a stable reference for U1. The output of operational amplifier U1 outputs a temperature compensation voltage Vt.

[0039] The chopper-stabilized operational amplifier U2 in the signal processing module uses a TLV2462CDR. This chip is in an SOIC-8 package, with an offset voltage ≤2μV, temperature drift ≤0.02μV / ℃, a quiescent current of 15μA when powered by 3.3V, and an open-loop gain of 120dB. It can accurately amplify the small capacitance signals generated by humidity changes. In the power supply filter circuit of the chopper-stabilized operational amplifier U2, diode D3 is a 1N4007WS, SOD-323 package, with a forward voltage drop of 0.7V and a reverse withstand voltage of 100V to prevent damage to U2 from reverse power connection. Capacitor C3 is a 0603 packaged ceramic capacitor, model CC0603KRX7R9BB104, with one end connected to the cathode of diode D3 and the other end grounded, forming a circuit. The circuit includes a source filter circuit; the non-inverting input of the chopper-stabilized operational amplifier U2 is connected to a reference voltage source Vr, which is the same ADR5040 used as the reference source for the temperature compensation module, outputting a stable 1.25V voltage; the inverting input of the chopper-stabilized operational amplifier U2 is connected to both the temperature compensation voltage Vt and the feedback signal from the capacitance sensing module, and its output is connected to a bistable trigger U3; the bistable trigger U3 is a CD4043BM96, which is an SOIC-16 packaged CMOS chip, powered by 3.3V, with a high-level output ≥2.7V, a low-level output ≤0.4V, and a response time ≤50ns. Its reset input R and set input S are both connected to the output of U2, and the two outputs are respectively connected to the corresponding branches of the capacitance sensing module.

[0040] The diodes D1 and D2 in the capacitive sensing module are both BAV99, SOT-23 packaged, dual-diode structure with a forward voltage drop of 0.6V and a reverse recovery time ≤5ns, controlling the charging and discharging directions of capacitors C1 and C2 respectively. Resistors R1 and R2 are 0603 packaged thick-film resistors, model RC0603JR-0720KL, connected in parallel with diodes D2 and D1 respectively. One end of the parallel connection between resistor R1 and diode D2 is connected to one output of bistable trigger U3, and the other end is connected to capacitor C1. 2. The common terminal of the parallel connection with diode D1 is connected to the other output terminal of bistable trigger U3, and the other end is connected to capacitor C2. Capacitors C1 and C2 are 0805 packaged polymer humidity-sensitive capacitors, model HS1101LF, with a capacitance of 200pF at 25℃ and 50%RH, and the capacitance changes by ±0.5pF for every 1%RH change in humidity. The other ends of both are connected to the signal output terminal OUT. The ends of capacitors C1 and C2 closest to the signal output terminal OUT are also connected to the inverting input of chopper-stabilized operational amplifier U2, forming signal feedback.

[0041] When the circuit is working, the positive terminal VIN of the power supply supplies power to each module. In the temperature compensation module, RT converts the change in ambient temperature into a voltage signal, which is processed by U1 and output to the inverting terminal of U2 as Vt. In the signal processing module, U2 processes the Vt signal at the inverting terminal and the feedback signal from the capacitance sensing module, and outputs a level signal to drive the state of U3 to flip. The output signal of U3 controls the charging and discharging of C1 and C2. The capacitance values ​​of C1 and C2 change with the ambient humidity. After the charging and discharging voltage changes, it is output through OUT and simultaneously fed back to U2 to form a closed loop. The low-pass filter connected to OUT filters out interference and outputs a stable signal to the subsequent MCU to achieve high-precision detection of ambient humidity.

[0042] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

[0043] The above are all preferred embodiments of this utility model and are not intended to limit the scope of protection of this utility model. Therefore, all equivalent changes made to the structure, shape and principle of this utility model should be included within the scope of protection of this utility model.

Claims

1. A capacitive inductive sensing circuit, characterized by The system includes a temperature compensation module, a signal processing module, a capacitance sensing module, and a power supply and output module. The temperature compensation module includes an operational amplifier U1, a temperature sensor RT, and a voltage divider resistor R3. The temperature sensor RT is surface-mount connected to the capacitance sensor. The temperature sensor RT converts the temperature change of the capacitance sensor into a voltage signal output connected to the operational amplifier U1. The operational amplifier U1 outputs a temperature compensation voltage Vt to the signal processing module. The signal processing module includes a chopper-stabilized operational amplifier U2 and a bistable trigger U3, which are electrically connected. The capacitance sensing module includes capacitors C1 and C2. The common connection point of capacitors C1 and C2 leads to a signal output terminal OUT. The signal output terminal OUT is externally connected to a low-pass filter. At the same time, the signal output terminal OUT of capacitors C1 and C2 is electrically connected to the inverting input of the chopper-stabilized operational amplifier U2.

2. The capacitive sensing circuit according to claim 1, characterized in that, One end of the temperature sensor RT is connected to the positive terminal VIN of the power supply, and the other end of the temperature sensor RT is connected to the non-inverting input of the operational amplifier U1 through the voltage divider resistor R3. The inverting input of the operational amplifier U1 is connected to an external reference source to provide a stable reference voltage, and the output terminal of the operational amplifier U1 outputs a temperature compensation voltage Vt.

3. A capacitive sensing circuit according to claim 1, wherein, One end of the chopper-stabilized operational amplifier U2 is connected to the positive power supply VIN after being filtered. The filtering at one end of the chopper-stabilized operational amplifier U2 includes diode D3 and capacitor C3, which are electrically connected to the positive power supply VIN.

4. A capacitive sensing circuit according to claim 1, wherein, The non-inverting input of the chopper-stabilized zero-electron op-amp U2 is connected to the reference voltage source Vr, and the inverting input of the chopper-stabilized zero-electron op-amp U2 is connected to the temperature compensation voltage Vt output by the temperature compensation module and the feedback signal from the capacitor sensing module; the output of the chopper-stabilized zero-electron op-amp U2 is connected to the bistable trigger U3.

5. A capacitive sensing circuit according to claim 1, wherein, The reset terminal R and set terminal S of the bistable trigger U3 are electrically connected to the output terminal of the chopper-stabilized operational amplifier U2, and the output terminal of the bistable trigger U3 is electrically connected to the capacitance sensing module.

6. A capacitive sensing circuit according to claim 1, wherein, The capacitive sensing module includes diodes D1 and D2, capacitors C1 and C2, resistors R1 and R2, and a signal output terminal OUT. Resistor R1 and diode D2 are connected in parallel. One end of the parallel connection between resistor R1 and diode D2 is electrically connected to one output terminal of U3, and the other end is electrically connected to capacitor C1. Resistor R2 and diode D1 are connected in parallel. One end of the parallel connection between resistor R2 and diode D1 is electrically connected to the other output terminal of U3, and the other end is electrically connected to capacitor C2. Capacitors C1 and C2 are electrically connected to the signal output terminal OUT. Capacitors C1 and C2 are also electrically connected to the inverting input terminal of chopper-stabilized operational amplifier U2. A low-pass filter is externally connected to the signal output terminal OUT.

Images