A digital closed-loop humidity sensor interface circuit

Abstract

This invention proposes a digital closed-loop humidity sensor interface circuit. The interface circuit includes a charge conversion circuit, a signal amplification circuit, a driving circuit, and a digital processing module. The humidity sensor interface circuit designed in this invention has the advantages of high precision, high resolution, high integration, and strong anti-interference capability. It can output both digital and analog results, facilitating subsequent processing of the humidity sensor results. Compared to other capacitive humidity sensors, this humidity sensor has high precision and high resolution; the digital part is unaffected by errors in analog components such as temperature and voltage drift. Furthermore, the entire circuit can be integrated into a single ASIC chip, reducing peripheral circuitry, system size, and cost, resulting in high integration. Moreover, the core components utilize digital processing; since digital signals have higher noise tolerance, the sensor's anti-interference capability is also stronger.

Description

Technical Field

[0001] This invention relates to the field of humidity sensor interface circuit technology, and more particularly to a digital closed-loop humidity sensor interface circuit. Humidity sensors are widely used in military, agriculture, industry, scientific research and other fields, and specifically relates to a high-precision humidity sensor ASIC chip with digital processing capabilities. Background Technology

[0002] Humidity refers to the concentration of water vapor in the air. With technological advancements and societal progress, the need for humidity detection and control has become increasingly important. A humidity sensor is a device that converts ambient humidity into a measurable electrical signal. It is widely used in climate monitoring, record management, and the use and protection of precision instruments. An ideal humidity sensor possesses advantages such as high sensitivity, long-term stability, short response time, low cost, and a wide operating temperature and humidity range. The development trend of humidity sensor technology mainly focuses on high precision, high stability, low power consumption, and miniaturization.

[0003] Humidity sensors are mainly classified into several types according to their working principle and structure, including capacitive, resistive, thermistor, and infrared sensors. Among them, capacitive humidity sensors utilize the property that the capacitance of a parallel-plate capacitor is related to the properties of its dielectric, using a humidity-sensitive material as the dielectric layer. Due to their low cost, fast response speed, and wide measurement range, capacitive humidity sensors are widely used in various fields such as industrial automation, healthcare, environmental monitoring, and agriculture. Especially in industrial automation, capacitive humidity sensors can provide real-time and accurate data support. In environmental monitoring, their accurate measurement of parameters such as air quality and water humidity, and their role in environmental quality assessment and protection, are crucial.

[0004] The capacitance detection circuit is an indispensable and important component of humidity sensor circuits. In this circuit, the received raw capacitance signal is first processed into an electrical signal that can be recognized and processed by subsequent circuits. After amplification and filtering, the final electrical signal characterizes the magnitude of the humidity-sensitive capacitance, thus reflecting changes in humidity. In practical applications of capacitive humidity sensors, the accuracy and precision of capacitance detection directly affect the sensor's performance. For example, traditional humidity measurement circuits have low measurement accuracy and are susceptible to noise interference, further limiting the resolution of the measurement results, reducing sensor reliability, and significantly impacting their use in high-end applications.

[0005] In conclusion, the quality of capacitive detection results determines the overall performance of a humidity sensor and is one of the key indicators of humidity detection technology. High precision, high resolution, high integration, and strong anti-interference capabilities are the future development directions for capacitive humidity sensors. Capacitive humidity sensors have a large market demand and will have more application scenarios in the future. Summary of the Invention

[0006] To address the problems of low measurement accuracy, weak noise tolerance, and low integration in existing humidity sensors, this invention proposes a digital closed-loop humidity sensor interface circuit.

[0007] This invention is achieved through the following technical solution: A digital closed-loop humidity sensor interface circuit is proposed, comprising four parts: a charge conversion circuit 101, a signal amplification circuit 102, a driving circuit 103, and a digital processing module 104. The input of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref. The output of the charge conversion circuit 101 is connected to the signal amplification circuit 102, the output of the signal amplification circuit 102 is connected to the driving circuit 103, the output of the driving circuit 103 is connected to the digital processing module 104, and the output of the digital processing module 104 is connected to one end of the reference capacitor Cref. The digital processing module 104 outputs the final digital and analog output results. The digital processing module 104 is implemented digitally using an ASIC chip. The digital processing module 104 includes an ADC, a PI controller, and a DAC. The input terminal of the ADC receives the differential signal output by the driving circuit 103. The output terminal of the ADC is connected to the PI controller, and the output terminal of the PI controller is connected to the DAC. The signal at the output terminal of the PI controller is the final digital output result. The output terminal of the DAC is connected to one end of the reference capacitor Cref, and the signal at the output terminal of the DAC is the final analog output result. The signal at the output terminal of the DAC is the same as the signal at the output terminal of the PI controller.

[0008] Furthermore, the charge conversion circuit 101 includes a low-noise charge amplifier, an integrating capacitor, and a switch. The input terminal of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref.

[0009] Furthermore, the input terminal of the signal amplification circuit 102 is connected to the output terminal of the charge conversion circuit 101, which is used to amplify the single-ended output signal of the charge conversion circuit 101 and convert it into a differential signal with a high common-mode rejection ratio. The signal amplification circuit 102 has low noise and low offset characteristics to ensure the high precision requirements of the interface circuit. The gain of the signal amplification circuit 102 can be automatically adjusted according to the amplitude of the output signal to keep the output signal within a specific range and maximize the signal accuracy.

[0010] Furthermore, the input terminal of the driving circuit 103 is connected to the output terminal of the signal amplification circuit 102; the driving circuit 103 is used to receive the high-precision small current signal output by the signal amplification circuit 102 and convert it into a high-precision large current signal that can directly drive the high-precision ADC. The signals before and after conversion need to be kept at the same level to ensure the high precision level of the interface circuit.

[0011] Furthermore, the ADC is a Sigma-Delta ADC, connected between the drive circuit 103 and the digital PI controller; it is used to convert the high-precision analog differential signal output by the drive circuit 103 into a high-precision digital signal, and then transmit it to the digital PI controller for processing.

[0012] Furthermore, the PI controller is connected between the ADC and the DAC. It receives the high-precision digital signal output by the ADC, processes it digitally, outputs the corrected signal, and transmits it to the DAC to compensate for the deviation in the closed loop in real time. The PI controller is implemented through digital logic circuits.

[0013] Furthermore, the DAC is a high-precision Sigma-Delta DAC connected between the PI controller and the reference capacitor Cref; it is used to convert the digital error signal output by the PI controller into a high-precision analog feedback signal and apply it to one end of the reference capacitor Cref, thereby forming a closed-loop control loop to suppress system noise and improve measurement accuracy.

[0014] The beneficial effects of this invention are: 1. Compared with traditional capacitive humidity sensors, this invention adopts a mixed-signal design, Sigma-DeltaADC, whose high accuracy mainly relies on oversampling and noise shaping. These can be achieved through precise clock control and digital filters in digital circuits, and the resolution can reach more than 16 bits, giving the circuit high measurement accuracy and high resolution.

[0015] 2. The digital humidity sensor designed in this invention is integrated into the same ASIC chip, which is small in size, light in weight, and highly reliable, and has the advantages of high integration.

[0016] 3. The digital humidity sensor designed in this invention adopts a fully differential structure for front-end analog processing, which has strong common-mode noise suppression capability and is less susceptible to noise interference. For subsequent digital processing, the proportional coefficient, integral coefficient, etc. in the PI controller are all set values, the digital circuit is less affected by external factors, and the circuit has stronger anti-interference capability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is the overall logic block diagram of the humidity sensor interface circuit; Figure 2 A schematic diagram of the implementation scheme for the charge conversion circuit and signal amplification circuit; Figure 3 This is a schematic diagram of the driver circuit implementation scheme; Figure 4 This is a schematic diagram of the ADC implementation scheme in the digital processing module.

[0019] Figure 5 This is a flowchart of the operation of the PI controller in the digital processing module. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention proposes a digital closed-loop humidity sensor interface circuit, specifically a high-precision humidity sensor ASIC chip circuit with digital processing capabilities. Compared to other capacitive humidity sensors, this humidity sensor offers higher accuracy and resolution, and its digital portion is unaffected by errors in analog components such as temperature and voltage drift. Furthermore, the entire circuit can be integrated into a single ASIC chip, reducing peripheral circuitry, system size, and cost, resulting in high integration. Moreover, the core components utilize digital processing, which, due to the higher tolerance of digital signals to noise, enhances the sensor's anti-interference capabilities.

[0022] Specifically, see Figures 1-5This invention proposes a digital closed-loop humidity sensor interface circuit, which includes four parts: a charge conversion circuit 101, a signal amplification circuit 102, a driving circuit 103, and a digital processing module 104. The input terminal of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref. The output terminal of the charge conversion circuit 101 is connected to the signal amplification circuit 102. The output terminal of the signal amplification circuit 102 is connected to the driving circuit 103. The output terminal of the driving circuit 103 is connected to the digital processing module 104. The output terminal of the digital processing module 104 is connected to one end of the reference capacitor Cref. The digital processing module 104 outputs the final digital output result and the analog output result. The digital processing module 104 is implemented digitally using an ASIC chip. The digital processing module 104 includes an ADC, a PI controller, and a DAC. The input terminal of the ADC receives the differential signal output by the driving circuit 103. The output terminal of the ADC is connected to the PI controller, and the output terminal of the PI controller is connected to the DAC. The signal at the output terminal of the PI controller is the final digital output result. The output terminal of the DAC is connected to one end of the reference capacitor Cref, and the signal at the output terminal of the DAC is the final analog output result. The signal at the output terminal of the DAC is the same as the signal at the output terminal of the PI controller.

[0023] The charge conversion circuit 101 includes a low-noise charge amplifier, an integrating capacitor Cf, and a switch. The input of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref.

[0024] The input terminal of the signal amplification circuit 102 is connected to the output terminal of the charge conversion circuit 101, and is used to amplify the single-ended output signal of the charge conversion circuit 101 and convert it into a differential signal with a high common-mode rejection ratio. The signal amplification circuit 102 has low noise and low offset characteristics to ensure the high precision requirements of the interface circuit. The gain of the signal amplification circuit 102 can be automatically adjusted according to the amplitude of the output signal to keep the output signal within a specific range and maximize the signal accuracy.

[0025] The input terminal of the driving circuit 103 is connected to the output terminal of the signal amplification circuit 102. The driving circuit 103 is used to receive the high-precision small current signal output by the signal amplification circuit 102 and convert it into a high-precision large current signal that can directly drive the high-precision ADC. The signals before and after the conversion need to be kept at the same level to ensure the high precision level of the interface circuit.

[0026] The ADC is a Sigma-Delta ADC, connected between the drive circuit 103 and the digital PI controller; it is used to convert the high-precision analog differential signal output by the drive circuit 103 into a high-precision digital signal, and then transmit it to the digital PI controller for processing.

[0027] The PI controller is connected between the ADC and DAC. It receives the high-precision digital signal output by the ADC, processes it digitally, outputs the corrected signal, and transmits it to the DAC to compensate for the deviation in the closed loop in real time. The PI controller is implemented through digital logic circuits.

[0028] The DAC is a high-precision Sigma-Delta DAC connected between the PI controller and the reference capacitor Cref. It is used to convert the digital error signal output by the PI controller into a high-precision analog feedback signal and apply it to one end of the reference capacitor Cref, thereby forming a closed-loop control loop to suppress system noise and improve measurement accuracy.

[0029] This invention proposes a high-precision digital closed-loop humidity sensor interface circuit, comprising a charge conversion circuit 101, a signal amplification circuit 102, a driving circuit 103, and a digital processing module 104. The input of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref. The output of the charge conversion circuit 101 is connected to the signal amplification circuit 102, the output of the signal amplification circuit 102 is connected to the driving circuit 103, and the output of the driving circuit 103 is connected to the digital processing module 104. The digital processing module 104 includes an analog-to-digital converter (ADC), a PI controller, and a digital-to-analog converter (DAC). The input of the ADC receives the signal output from the driving circuit 103. The output of the ADC is connected to the PI controller, and the output of the PI controller is connected to the DAC. The signals at the outputs of the DAC and PI controller are the final digital output results. The output of the DAC is connected to one end of the reference capacitor Cref, and the signal at the output of the DAC is the final analog output result. The signal at the output of the DAC is the same as the signal at the output of the PI controller. The humidity sensor interface circuit designed in this invention has the advantages of high precision, high resolution, high integration, and strong anti-interference ability. It can output both digital and analog results, which facilitates subsequent processing of the humidity sensor results.

[0030] Example Specific implementation method one: Combining Figure 1This embodiment describes a digital closed-loop humidity sensor interface circuit comprising a charge conversion circuit 101, a signal amplification circuit 102, a driving circuit 103, a digital processing module 104, a humidity-sensitive capacitor Cm, and a reference capacitor Cref. The humidity-sensitive capacitor Cm and the reference capacitor Cref are connected in series, with their common terminal connected to the charge conversion circuit 101, inputting the charge difference between them into the charge conversion circuit 101. The other end of the humidity-sensitive capacitor Cm is connected to a reference voltage Vref, and the other end of the reference capacitor Cref is connected to a feedback signal Vout. The input terminal of the charge conversion circuit 101 receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref. The output terminal of the charge conversion circuit 101 is connected to the signal amplification circuit 102, the output terminal of the signal amplification circuit 102 is connected to the driving circuit 103, the driving circuit 103 is connected to the digital processing module 104, and the output terminal of the digital processing module 104 is connected to one end of the reference capacitor Cref. The digital processing module 104 internally outputs the final digital and analog results.

[0031] Inside the digital processing module 104 in this embodiment, the input terminal of the ADC is connected to the driving circuit 103, the output terminal of the ADC is connected to the PI controller, the output terminal of the PI controller is connected to the DAC, the output terminal of the DAC is connected to one end of the reference capacitor Cref, and the output terminal of the PI controller outputs the final digital result.

[0032] Specific Implementation Method Two: Combining Figure 1 and Figure 2 This embodiment describes a digital closed-loop humidity sensor interface circuit. The charge conversion circuit 101 consists of a low-noise charge amplifier A0, an integrating capacitor Cf, and a switch S0. The integrating capacitor Cf and the switch S0 are connected in parallel between the inverting input and output of amplifier A0. The inverting input of the amplifier receives the signal from the preceding stage, while the non-inverting input is grounded. The input of the charge conversion circuit 101 is connected to the common terminal of the humidity-sensitive capacitor Cm and the reference capacitor Cref. The control signal CLK for the switch is provided by the internal digital timing logic of the ASIC.

[0033] Specific implementation method three: Combining Figure 1 and Figure 2This embodiment describes a digital closed-loop humidity sensor interface circuit. The signal amplification circuit 102 is a programmable gain amplifier (PGA), consisting of two single-ended operational amplifiers A1 and A2, a fully differential amplifier A3, a gain control module, and four resistors R0, R1, R2, and R3. The two operational amplifiers and the gain control module are located in the first stage, and the fully differential amplifier is located in the second stage. In the first stage, the non-inverting input of operational amplifier A0 serves as the input of the PGA, the non-inverting input of operational amplifier A1 is grounded, and the inverting inputs of the two operational amplifiers are connected to the input... All output terminals are connected to the gain control module, and the first-stage gain is automatically adjusted by the digital signal CTL according to the amplitude of the output signal. In the second stage, resistor R0 is connected between the gain control module and the non-inverting input of amplifier A3, resistor R1 is connected between the gain control module and the inverting input of amplifier A3, resistor R2 is connected between the non-inverting input and the inverting output of amplifier A3, and resistor R3 is connected between the inverting input and the non-inverting output of amplifier A3. The differential output of amplifier A3 serves as the output of the PGA. Since the four resistors in the second stage have equal values, the closed-loop gain of the second stage can be calculated as follows: Its function is to reduce noise interference, minimize the influence of ground lines, and give the signal strong common-mode interference immunity, while also providing a higher common-mode rejection ratio. The gain of the aforementioned signal amplification circuit is controlled by digital logic. Its advantages include not only adjusting the gain according to the magnitude of the input signal to avoid saturation, but also maximizing the utilization of the ADC and improving signal resolution through gain adjustment.

[0034] Specific implementation method four: Combination Figure 1 and Figure 3 This embodiment describes a digital closed-loop humidity sensor interface circuit. The driving circuit 103 consists of a fully differential amplifier A4 and four resistors R4, R5, R6, and R7, all of equal value. The differential output of amplifier A6 serves as the output of the driving circuit 103. The driving circuit 103 is a voltage follower in the form of a fully differential amplifier. As a voltage follower, it has extremely high input impedance, strong load-carrying capacity, and its differential structure is less susceptible to noise interference, making it suitable for transmitting weak signals and applicable to high-precision measurement circuits.

[0035] Specific Implementation Method Five: Combining Figure 1 and Figure 4This embodiment describes a digital closed-loop humidity sensor interface circuit. The ADC in the digital processing module 104 is composed of an RC filter circuit, a sample-and-hold circuit, a switched capacitor network, an integrator, a comparator, a 1-bit DAC, and a CIC filter. The analog differential signal output from the driver circuit 103 is input to the RC filter circuit. The RC filter circuit is an anti-aliasing filter, which filters out high-frequency noise and prevents signals unrelated to the humidity-sensitive capacitor from being acquired. The output of the RC filter circuit is connected to a sample-and-hold circuit, and the output of the sample-and-hold circuit is connected to a switched capacitor network. The switched capacitor network is a summing node, which subtracts the output voltage of the sample-and-hold circuit from the voltage fed back by the DAC to calculate the error voltage. The output of the switched capacitor network is connected to an integrator, which integrates the error voltage and outputs the integration result to a comparator. The comparator compares the received voltage signal with a threshold and outputs 0 or 1 based on the result. The output of the comparator serves as a common node, connected to both a 1-bit DAC and a CIC filter. The 1-bit DAC feeds back the output of the integrator to the summing node for use in the next calculation. The CIC filter is a digital decimation filter, which outputs the bitstream as a low-speed, high-precision digital signal.

[0036] Specific Implementation Method Six: Combination Figure 1 and Figure 5 This embodiment describes a digital closed-loop humidity sensor interface circuit. The PI controller in the digital processing module 104 is digitally implemented, and its working principle is as follows: First, sampling and error calculation: the digital signal output by the preceding ADC is compared with a set value to calculate the error signal. Second, proportional stage calculation: the error value is multiplied by the proportional coefficient Kp using a multiplier to calculate the proportional stage output. Third, integral stage calculation: the error value is multiplied by the integral coefficient Ki using a multiplier and accumulated with the integral value from the previous moment to obtain the integral stage output. Fourth, output summation: the proportional term and integral term are added using an adder to obtain the original output result. Fifth, output limiting: the upper and lower limits of the original output result are compared with the upper and lower limits of the limiter. If the upper or lower limit of the original output result exceeds the upper or lower limit of the limiter, the output result is replaced by the upper or lower limit of the limiter; otherwise, the output result remains unchanged and is the original output.

[0037] Specific Implementation Method Seven: In the high-precision humidity sensor ASIC chip with digital processing function described in this embodiment, the DAC in the digital processing module (104) is composed of an interpolation filter, a digital Sigma-Delta modulator, a 1-bit DAC, an analog low-pass filter, and an output buffer amplifier; the interpolation filter and the Sigma-Delta modulator are the digital part of the DAC, and the 1-bit DAC, the low-pass filter, and the output buffer amplifier are the analog part of the DAC. The digital signal output from the PI controller, after range conversion, is input to the interpolation filter via the DAC interface. Its function is to oversample the input digital signal, increasing the sampling rate. The output of the interpolation filter is connected to a digital Sigma-Delta modulator. The Sigma-Delta modulator compresses the high-bit digital signal into a 1-bit high-sampled data stream and performs noise shaping. The output of the digital Sigma-Delta modulator is connected to a 1-bit DAC, which converts the 1-bit data stream into an analog signal. The output of the 1-bit DAC is connected to an analog low-pass filter, which filters out the high-frequency quantization noise generated by the modulator. The output of the low-pass filter is connected to an output buffer amplifier, which isolates the low-pass filter from the external load, preventing the load from affecting the filtering effect.

[0038] Working principle This circuit design converts the capacitance of the humidity sensor to be measured into a stable voltage. The final expression for the two is proportional to the following: In the above formula, Cm is the humidity-sensitive capacitor, Cref is the reference capacitor, Vref is the reference voltage (voltage across one end of the humidity-sensitive capacitor), and Vout is the analog output of the circuit (voltage across one end of the reference capacitor). When Cm is unknown, Cref and Vref are known. Knowing Vout allows us to calculate Cm; therefore, the core of the measurement is to measure Vout by establishing a closed-loop system. Since the initial charges on the humidity-sensitive capacitor Cm and the reference capacitor Cref are different, a charge difference is formed. The charge conversion circuit 101 includes a low-noise charge amplifier, an integrating capacitor Cf, and a switch. During operation, the input receives the charge difference generated by the previous stage. The charge conversion circuit 101 converts the charge signal related to the humidity-sensitive capacitor into a voltage signal and amplifies the weak charge signal with low noise for easy identification by subsequent circuits.

[0039] The signal amplification circuit 102 includes two single-ended output operational amplifiers, a gain control module, a fully differential amplifier, and four resistors. This part of the circuit mainly amplifies the voltage signal output by the charge conversion circuit 101. The first-stage operational amplifier can automatically adjust its gain according to the amplitude of the output signal, so that it can amplify as much as possible without exceeding the range of the ADC. The second stage of the PGA has a gain of 1, mainly using a fully differential structure to suppress common-mode interference.

[0040] The driving circuit 103 is a voltage follower in the form of a fully differential amplifier, which includes a fully differential amplifier and four resistors. This part of the circuit mainly solves the output current problem of the front-end circuit. This type of voltage follower has extremely high input impedance and can be used as a driving circuit to improve the circuit's load-carrying capacity.

[0041] The ADC in the digital processing module 104 includes an RC filter circuit, a sample-and-hold circuit, a switched capacitor network, an integrator, a comparator, a DAC, and a digital decimation filter. The RC filter circuit first filters the differential signal output from the driver circuit to prevent high-frequency noise from aliasing into the useful signal bandwidth in subsequent sampling. The RC-filtered signal enters the sample-and-hold circuit, which is used to ensure the stability of the signal during the ADC analog-to-digital conversion and improve the accuracy of signal acquisition and conversion. The output signal of the sample-and-hold circuit enters the ADC modulator composed of a switched capacitor network, an integrator, a comparator, and a 1-bit DAC. In the ADC modulator, the signal undergoes subtraction, integration, comparison, and feedback to finally generate a 1-bit high-sample bit stream. After passing through the digital decimation filter, the sampling rate of the signal is reduced and high-frequency noise is filtered out. After calibration, a digital output is obtained.

[0042] The PI controller in the digital processing module 104 is implemented using digital logic circuits. First, a subtractor is used to subtract the ADC output from the set value to obtain the error signal. Then, a multiplier is used to multiply the error signal with the proportional coefficient Kp to calculate the output of the discrete proportional stage. Next, a multiplier is used to multiply the error signal with the integral coefficient Ki, and then an accumulator is used to add the integral from the previous time step to obtain the output of the discrete integral stage. The results of the discrete proportional stage and the discrete integral stage are added together to obtain the original output result. Finally, the final digital output result Dout is obtained by comparison with the limiter.

[0043] The DAC in the digital processing module includes an interpolation filter, a digital Sigma-Delta modulator, a 1-bit DAC, an analog low-pass filter, and an output buffer amplifier. The interpolation filter first oversamples the output signal of the PI controller after range conversion. The oversampled signal is then input into the digital Sigma-Delta modulator, which compresses the high-bit digital signal into a 1-bit high-sampled data stream and performs noise shaping. The output of the digital Sigma-Delta modulator is connected to the 1-bit DAC, which converts the 1-bit data stream into an analog signal. The converted analog signal is then input into the low-pass filter, which filters out the high-frequency quantization noise generated by the modulator. Finally, the output buffer amplifier outputs the final analog output result, Vout.

[0044] After one closed-loop operation, the analog output result is fed back to one end of the reference capacitor Cref, causing a change in the voltage at that end of the reference capacitor Cref. The reference capacitor Cref and the humidity-sensitive capacitor Cm generate new error charges, which are then fed back to one end of the reference capacitor Cref via the closed-loop system, resulting in a new voltage Vout. This process continues until the reference capacitor Cref and the humidity-sensitive capacitor Cm no longer generate new error charges, ultimately yielding a stable analog output Vout. At this point, the value of the humidity-sensitive capacitor Cm, calculated based on the ratio between the humidity-sensitive capacitor Cm and the reference capacitor Cref, is the measurement result.

[0045] The digital closed-loop humidity sensor interface circuit proposed in this invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A digital closed-loop humidity sensor interface circuit, characterized in that, The interface circuit includes four parts: a charge conversion circuit (101), a signal amplification circuit (102), a driving circuit (103), and a digital processing module (104). The input terminal of the charge conversion circuit (101) receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref. The output terminal of the charge conversion circuit (101) is connected to the signal amplification circuit (102). The output terminal of the signal amplification circuit (102) is connected to the driving circuit (103). The output terminal of the driving circuit (103) is connected to the digital processing module (104). The output terminal of the digital processing module (104) is connected to one end of the reference capacitor Cref. The digital processing module (104) outputs the final digital output result and the analog output result. The digital processing module (104) is implemented digitally using an ASIC chip. The digital processing module (104) includes an ADC, a PI controller, and a DAC. The input terminal of the ADC receives the differential signal output by the driving circuit (103). The output terminal of the ADC is connected to the PI controller. The output terminal of the PI controller is connected to the DAC. The signal at the output terminal of the PI controller is the final digital output result. The output terminal of the DAC is connected to one end of the reference capacitor Cref. The signal at the output terminal of the DAC is the final analog output result. The signal at the output terminal of the DAC is the same as the signal at the output terminal of the PI controller.

2. The interface circuit according to claim 1, characterized in that, The charge conversion circuit (101) includes a low-noise charge amplifier, an integrating capacitor and a switch. The input of the charge conversion circuit (101) receives the charge difference between the humidity-sensitive capacitor Cm and the reference capacitor Cref.

3. The interface circuit according to claim 1, characterized in that, The input terminal of the signal amplification circuit (102) is connected to the output terminal of the charge conversion circuit (101) to amplify the single-ended output signal of the charge conversion circuit (101) and convert it into a differential signal with a high common-mode rejection ratio; the signal amplification circuit (102) has low noise and low offset characteristics to ensure the high precision requirements of the interface circuit. The gain of the signal amplifier circuit (102) can be automatically adjusted according to the amplitude of the output signal, so that the output signal is maintained within a specific range and the signal accuracy is maximized.

4. The interface circuit according to claim 1, characterized in that, The input terminal of the driving circuit (103) is connected to the output terminal of the signal amplification circuit (102); the driving circuit (103) is used to receive the high-precision small current signal output by the signal amplification circuit (102) and convert it into a high-precision large current signal that can directly drive the high-precision ADC. The signals before and after the conversion need to be kept at the same level to ensure the high precision level of the interface circuit.

5. The interface circuit according to claim 1, characterized in that, The ADC is a Sigma-Delta ADC, connected between the drive circuit (103) and the digital PI controller; it is used to convert the high-precision analog differential signal output by the drive circuit (103) into a high-precision digital signal, and then transmit it to the digital PI controller for processing.

6. The interface circuit according to claim 1, characterized in that, The PI controller is connected between the ADC and DAC. It receives the high-precision digital signal output by the ADC, processes it digitally, outputs the corrected signal, and transmits it to the DAC to compensate for the deviation in the closed loop in real time. The PI controller is implemented through digital logic circuits.

7. The interface circuit according to claim 1, characterized in that, The DAC is a high-precision Sigma-Delta DAC connected between the PI controller and the reference capacitor Cref. It is used to convert the digital error signal output by the PI controller into a high-precision analog feedback signal and apply it to one end of the reference capacitor Cref, thereby forming a closed-loop control loop to suppress system noise and improve measurement accuracy.

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