A Current-Reuse DDA Based Analog Front End For Multi-Biological Signal Acquisition

With the emergence of the COVID-19 all over the world,the development of medical technology has received more and more attention.Traditional vital signs monitoring equipment,such as ECG monitors,EEG monitors,etc.are limited by space and time,and the penetration rate is not high,so wearable or implantable portable vital signs monitoring devices have become the focus of research.As one of the most critical modules of these devices,the bio-signal acquisition analog front end(AFE)directly affects the monitoring accuracy.Therefore,it is very important to design an AFE circuit for bio-signal acquisition with low noise,low power,and strong anti-interference ability.This design implements an AFE for multi-biological signal acquisition,which mainly includes three core modules: instrumentation amplifier,Low pass filter,and programmable gain amplifier.Firstly,an instrumentation amplifier based on the current-reuse differential difference amplifier(DDA)is proposed,which not only ensuring the input impedance,but also avoiding the design of complex pre-charge circuits.Also,with the chopper modulation technology,the input reference noise of the analog front end is reduced,and the antiinterference performance is improved.At the same time,the use of current-reuse technology reduces the bias current of the DDA,which can effectively decreases the power consumption and area of the analog front end.To eliminate the DC offset caused by the bio-electrode,a digitally controlled DC servo loop is also adopted in this paper,which can achieve a wider DC offset cancellation range while reducing noise.Meanwhile,in order to filter out highfrequency noise and burrs after chopping,a second-order Gm-C low pass filter is designed to adjust the bias current of the Gm unit adaptively,according to the size of the input capacitance in the programmable gain amplifier,avoiding the shift of low-pass cutoff frequency when the gain switching is changed.The integrity of the biological signal can be ensured.Finally,8 kinds of gain switching programmable gain amplifier circuits is proposed to adjust the gain automatically by judging the amplitude of the input signal.Then the biological signal can be amplified to a specific output range,so as to facilitate the quantization processing of the analog-to-digital converter in the later stage.Besides,the constant high-pass cutoff frequency in programmable gain amplifier is achieved by fixing the feedback capacitor,thereby filtering the residual DC offset.In this way,the loss of biological signals caused by the change of gain switching is avoided,and the quality of the signal acquisition is ensured.Based on the TSMC 65 nm CMOS process,the circuit and layout of the multi-biological signal acquisition AFE based on the current multiplexing DDA is implemented.The core area is 400μm×252μm.The simulation results show that: under the power supply of 1V,in the bandwidth range of 0.4-250 Hz,the total input equivalent integrated noise is 2.38μVrms,the equivalent input impedance is greater than 1.65GΩ,and a wide DC offset cancellation range greater than ±300mV.For the IA,CMRR is higher than 103 dB,PSRR is higher than107 dB,and the power consumption is only 2.5μW.