Research And Design Of Biomedical Capacitive Sensor Interface Circuit Chip

Sensor interface circuit chip is a bridge between sensor and signal processing chip.It converts non-electrical physical quantities detected by sensor into electrical signals that can be detected and processed by circuit system according to certain rules.With the increasing concern for health issues and the rapid development of Internet of Things and5G technology,portable,wearable and intelligent biomedical monitoring equipment has become an important research direction in the field of biomedicine.After briefly introducing the types and working principles of the existing biomedical sensor interface circuits,a voltage output biomedical capacitance sensor interface circuit and a digital output biomedical capacitance sensor interface circuit are designed for the analog and digital systems respectively.The interface circuit of voltage output biomedical capacitance sensor adopts the structure of frequency modulation circuit based on capacitance change and frequency voltage conversion circuit to realize high sensitivity and wide range detection of biomedical capacitance sensor.In the frequency modulation circuit based on capacitance variation,the capacitance information of the capacitance sensor is converted into a frequency square wave signal proportional to the capacitance by using a bidirectional self-switching RC relaxation oscillator.Frequency-voltage conversion circuit adopts edge detection method,and takes signal edge triggering as condition.The charging time of capacitor is controlled by MOS switch.The conversion of frequency information to voltage signal can be completed within one cycle of input signal,which reduces the output delay and improves the working efficiency of the circuit system.After completing the circuit design and functional simulation,the sensitivity of capacitance detection can reach 0.69¹.342fF,and the power consumption is only 85.14uW.On the basis of TSMC 0.18um 1P6M process flow sheet production,the physical function verification of the chip and the measurement of various parameters are completed.Aiming at the requirement of digital signal processing in most circuit systems and the problem that the interface circuit of traditional digital output capacitance sensor can only be detected with single precision,a digital output biomedical capacitance sensor interface circuit is designed,which adopts dual precision capacitance-time conversion circuit matched with low precision and high precision,and programmable time-digital conversion circuit structure to detect directly.The capacitance information is converted to digital output and stored in registers.The capacitor-time conversion circuit compares the voltage on the measured capacitor with the set voltage by a comparator,and divides the frequency by a pulse generator unit and a D flip-flop to output a square wave signal whose period is linearly related to the measured capacitor.In the time-to-digital conversion circuit,the programmable frequency divider enlarges the T_M signal by 2^N+1 times through the external control signal N.Without changing the reference signal T_L and T_H,the detection accuracy of the circuit for capacitance is improved.Logic control module enables T_L and T_H reference signals to realize two-stage dual-precision detection of amplified 2^N+1*TM signals.Control counter stores the measurement results of T_L and T_H signals into registers Reg0 and Reg1respectively.Based on TSMC 0.18um 1P6M process,the chip layout is plotted.The post-simulation results using Cadence Spectre show that the maximum accuracy of capacitance detection can reach 0.15fF,the power consumption of circuit is 160.6uW,and the area is 0.533mm².It has the advantages of wide range,high precision,and is not easily affected by the fluctuation of power supply voltage and temperature.