A high-sensitivity capacitive sensing array detection circuit and signal processing method

Abstract

The invention relates to a highly sensitive capacitive sensing array detection circuit and a signal processing method, and belongs to the technical field of capacitive sensor signal detection. The circuit specifically comprises a driving circuit connected to an input end of a capacitive sensor array via an analog switch circuit, an output end of the capacitive sensor array connected to a signal input end of a C / V conversion circuit via the analog switch circuit, a signal output end of the C / V conversion circuit connected to a subtraction circuit via a rectifier and filter circuit, a signal output end of the subtraction circuit connected to an amplification filter circuit, a signal input end of the analog switch circuit and an MCU processor, and the MCU processor is connected to the subtraction circuit via a DAC circuit. The invention subtracts a measurement signal of a sensor from an initial state signal through a controller to obtain a sensitive change value of the sensor, thereby achieving a signal DC isolation effect, which is more conducive to amplification of useful signals and other processing, and obtains higher detection sensitivity.

Description

Technical Field

[0001] The invention relates to a high-sensitivity capacitance sensing array detection circuit and a signal processing method, belonging to the technical field of capacitance sensor signal detection. Background Art

[0002] Capacitive sensors can detect the concave and convex shape of the measured object from the capacitance change between a pair of electrode layers, and can be used for surface pressure distribution sensors and sensors such as strain gauges. Generally, the capacitance in a capacitive sensor is represented by the following formula: C = ε0εrS / d..., where C represents capacitance, ε0 represents the permittivity in free space, εr represents the relative permittivity of the dielectric layer, S represents the area of ​​the electrode layer, and d represents the distance between the electrodes.

[0003] However, although traditional capacitor DC isolation is convenient, it has signal delay and is only suitable for independent operation of a single signal. It is not suitable for signal processing of multi-channel signal switching and is prone to cause crosstalk of switching signals. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the present invention provides a high-sensitivity capacitive sensor array detection circuit and a signal processing method, which uses a controller to subtract the measurement signal of the sensor from the initial state signal to obtain the sensitive change value of the sensor, thereby achieving a signal DC isolation effect, which can be more conducive to the amplification of useful signals and other processing, thereby obtaining higher detection sensitivity.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is a high-sensitivity capacitive sensing array detection circuit, including a driving circuit, a capacitive sensor array, an analog switching circuit, a C / V conversion circuit, a rectification and filtering circuit, a subtraction circuit, a DAC circuit, an amplification and filtering circuit and an MCU processor, wherein the driving circuit is connected to the input end of the capacitive sensor array via the analog switching circuit, the output end of the capacitive sensor array is connected to the signal input end of the C / V conversion circuit via the analog switching circuit, the signal output end of the C / V conversion circuit is connected to the subtraction circuit via the rectification and filtering circuit, the signal output end of the subtraction circuit is connected to the amplification and filtering circuit, the signal input end of the analog switching circuit is connected to the MCU processor, and the MCU processor is connected to the subtraction circuit via the DAC circuit.

[0006] Preferably, the driving circuit includes an active oscillator and a low-pass filter circuit, the active oscillator is used to provide an AC signal of 1 MHz, and after filtering by the low-pass filter circuit, a sinusoidal voltage of 1 MHz and 1 V is obtained.

[0007] Preferably, the analog switch circuit adopts ADG1212, which has a power supply of ±15V and two channels.

[0008] Preferably, the DAC circuit adopts AD5761R, and the output voltage is 0-20v.

[0009] A high-sensitivity capacitive sensing array detection circuit signal processing method is carried out according to the following steps:

[0010] a. The C / V conversion circuit converts the AC excitation current received by the sensitive end of the sensor into an AC voltage signal. Assume that the initial voltage of the excitation is , the feedback resistance of the circuit is , and not less than 33kΩ, the output voltage after C / V conversion for:

[0011] ,

[0012] b. The rectification and filtering circuit mainly realizes the rectification of AC voltage signal into DC signal, and obtains AC signal of positive half cycle through half-wave rectification by diode, and then obtains DC signal through second-order positive feedback active filter. The output voltage of the rectification and filtering circuit is for:

[0013] ,in, , is the amplitude of the excitation signal and the output signal of the C / V conversion circuit, is the rectification efficiency of the half-wave rectified signal;

[0014] c. The subtraction circuit and DAC circuit are mainly used to isolate the DC signal. First, the output value of the detection signal of each initial capacitance sensor of the capacitance sensor array is rectified and filtered. The measured voltage value is converted into the digital value of the corresponding DAC. Then, when the analog switch is switched to the corresponding channel, the DAC simultaneously outputs the initial voltage value of the corresponding channel. After subtraction by the subtraction circuit, the change value of the sensitive signal of the capacitive sensor is obtained. Its output voltage for:

[0015] ,

[0016] Assume the initial capacitance of the sensor is , then the above formula is:

[0017] .

[0018] Compared with the prior art, the present invention has the following technical effects: the detection circuit designed for the signal processing of the short-range capacitance sensor array of the present invention can rectify the AC signal received by the sensitive receiving end of the capacitance sensor into a DC signal for more convenient processing. In addition, the circuit subtracts the measurement signal of the sensor from the initial state signal through the controller to obtain the sensitive change value of the sensor, which plays a signal isolation effect, which can be more conducive to the amplification of useful signals and other processing, and obtain higher detection sensitivity. In addition, although the traditional capacitance isolation is convenient, there is a signal delay, and it is only suitable for single-channel signal independent work, not suitable for signal processing of multi-channel signal switching, and it is easy to cause crosstalk of the switching signal. The invention can well avoid these shortcomings of traditional capacitance isolation, and can test both the transient and static states of the capacitance sensor, and is more suitable for the detection of capacitance sensor array signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a block diagram of the capacitive sensor array detection circuit in the present invention.

[0020] Figure 2 The circuit diagram of the C / V conversion circuit, the rectifier filter circuit and the subtraction circuit in the present invention. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] like Figure 1 and Figure 2 As shown, a high-sensitivity capacitive sensing array detection circuit includes a driving circuit 1, a capacitive sensor array 2, an analog switch circuit 3, a C / V conversion circuit 4, a rectifier and filter circuit 5, a subtraction circuit 6, a DAC circuit 7, an amplifying and filtering circuit 8 and an MCU processor 9. The driving circuit 2 is connected to the input end of the capacitive sensor array 2 via the analog switch circuit 3, the output end of the capacitive sensor array 2 is connected to the signal input end of the C / V conversion circuit 4 via the analog switch circuit, the signal output end of the C / V conversion circuit 4 is connected to the subtraction circuit 6 via the rectifier and filter circuit 5, the signal output end of the subtraction circuit 6 is connected to the amplifying and filtering circuit 8, the signal input end of the analog switch circuit 3 is connected to the MCU processor 9, and the MCU processor 9 is connected to the subtraction circuit 6 via the DAC circuit 7.

[0023] Wherein, the driving circuit 1 includes an active oscillator and a low-pass filter circuit. The active oscillator is used to provide an AC signal of 1MHz. After filtering by the low-pass filter circuit, a sinusoidal voltage of 1MHz and 1V is obtained to improve the field energy of the sensitive space. The analog switch circuit 3 adopts ADG1212, which is powered by ±15V and has two channels. Its on-capacitance is small, which is 1pF, and has little effect on the subsequent capacitive sensor. By controlling the channel switching, different driving and sensitive electrode time-sharing multiplexing can be satisfied. The DAC circuit 7 adopts AD5761R, and the output voltage is 0-20v. The chip has a fast conversion speed and the establishment time is only about 10us. In addition, the DAC has high precision (16 bits), and the direct output voltage can reach 20V, without other auxiliary circuits, and the design is simple. Because the DAC can maintain the continuous output of the value of the initial voltage, it is different from the transient signal processing of the capacitor isolation circuit. Therefore, the detection circuit of the present invention can measure the transient and static states of the sensor.

[0024] A high-sensitivity capacitive sensing array detection circuit signal processing method is carried out according to the following steps:

[0025] a. The C / V conversion circuit converts the AC excitation current received by the sensitive end of the sensor into an AC voltage signal. Assume that the initial voltage of the excitation is , the feedback resistance of the circuit is , and not less than 33kΩ, the output voltage after C / V conversion for:

[0026] ,

[0027] b. The rectification and filtering circuit mainly realizes the rectification of AC voltage signal into DC signal, and obtains AC signal of positive half cycle through half-wave rectification by diode, and then obtains DC signal through second-order positive feedback active filter. The output voltage of the rectification and filtering circuit is for:

[0028] ,in, , is the amplitude of the excitation signal and the output signal of the C / V conversion circuit, It is the rectification efficiency of the half-wave rectification signal, which is related to the diode parameters and the signal frequency. Usually the rectification efficiency = 45%~98%;

[0029] c. The subtraction circuit and DAC circuit are mainly used to isolate the DC signal. First, the output value of the detection signal of each initial capacitance sensor of the capacitance sensor array is rectified and filtered. The measured voltage value is converted into the digital value of the corresponding DAC. Then, when the analog switch is switched to the corresponding channel, the DAC simultaneously outputs the initial voltage value of the corresponding channel. After subtraction by the subtraction circuit, the change value of the sensitive signal of the capacitive sensor is obtained. Its output voltage for:

[0030] ,

[0031] Assume the initial capacitance of the sensor is , then the above formula is:

[0032] .

[0033] From the above formula, we can see that the detection circuit detects the capacitance change value of the sensor. The subsequent amplification and filtering circuit can directly amplify the signal change value, which can avoid the situation where direct signal amplification is prone to saturation and obtain higher detection sensitivity.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A high-sensitivity capacitive sensing array detection circuit signal processing method, characterized in that: It includes a driving circuit, a capacitive sensor array, an analog switch circuit, a C / V conversion circuit, a rectification and filtering circuit, a subtraction circuit, a DAC circuit, an amplification and filtering circuit and an MCU processor, wherein the driving circuit is connected to the input end of the capacitive sensor array via the analog switch circuit, the output end of the capacitive sensor array is connected to the signal input end of the C / V conversion circuit via the analog switch circuit, the signal output end of the C / V conversion circuit is connected to the subtraction circuit via the rectification and filtering circuit, the signal output end of the subtraction circuit is connected to the amplification and filtering circuit, the signal input end of the analog switch circuit is connected to the MCU processor, and the MCU processor is connected to the subtraction circuit via the DAC circuit; The signal processing method is to follow the following steps: a. The C / V conversion circuit converts the AC excitation current received by the sensitive end of the sensor into an AC voltage signal. Assume that the initial voltage of the excitation is , the feedback resistance of the circuit is , and not less than 33kΩ, the output voltage after C / V conversion for: ， b. The rectifier and filter circuit mainly realizes the rectification of the AC voltage signal into a DC signal. The half-wave rectification is performed by the diode to obtain the positive half-cycle AC signal, and then the DC signal is obtained through the second-order positive feedback active filter. The output voltage of the rectifier and filter circuit is for: ,in, , is the amplitude of the excitation signal and the output signal of the C / V conversion circuit, is the rectification efficiency of the half-wave rectified signal; c. The subtraction circuit and DAC circuit are mainly used to isolate the DC signal. First, the output value of the detection signal of each initial capacitance sensor of the capacitance sensor array is rectified and filtered. The measured voltage value is converted into the digital value of the corresponding DAC. Then, when the analog switch is switched to the corresponding channel, the DAC simultaneously outputs the initial voltage value of the corresponding channel. After subtraction by the subtraction circuit, the change value of the sensitive signal of the capacitive sensor is obtained. Its output voltage for: ， Assume the initial capacitance of the sensor is , then the above formula is: 。 2. The high-sensitivity capacitive sensing array detection circuit signal processing method according to claim 1, characterized in that: The driving circuit includes an active oscillator and a low-pass filter circuit. The active oscillator is used to provide an AC signal of 1 MHz, and after filtering by the low-pass filter circuit, a sinusoidal voltage of 1 MHz and 1 V is obtained.

3. The high-sensitivity capacitive sensing array detection circuit signal processing method according to claim 1, characterized in that: The analog switch circuit adopts ADG1212, which has a power supply of ±15V and two channels.

4. The high-sensitivity capacitive sensing array detection circuit signal processing method according to claim 1, characterized in that: The DAC circuit adopts AD5761R, and the output voltage is 0-20v.

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