Research On Key Technology Of Giant Magnetoresistive(GMR)Biosensor Readout Circuit

Giant magnetoresistance(GMR)biosensor is mainly used to measure biological signals,such as cells,viruses,DNA,protein and so on.It is a new hot spot at home and abroad in recent years.High quality signal readout has important research significance and wide application prospect for medical diagnosis,so it is very important to suppress noise interference and design the readout circuit of relevant amplifier and analog to digital converter.The readout circuit of the giant magnetoresistance biosensor proposed in this paper mainly consists of two parts:the current feedback instrument amplifier(CFIA)with chopper technology and the successive approximation analog to digital converter(SAR ADC).The function of the current feedback instrument amplifier is to amplify the weak signal in the front end.By analyzing and comparing the advantages and disadvantages of the different instrument amplifiers,the CFIA circuit has large input impedance and strong common mode rejection capability,so it is suitable for the application of the bridge readout circuit.SAR ADC is mainly used to convert analog signals into digital signals,which can facilitate the analysis of signal performance.It has a great application value in simple structure,small area and low power consumption.In this paper,the readout circuit of giant magnetoresistance biosensor is studied,the main contents and achievements include:1.By studying the influence of the 1/f noise and offset on the readout signal of the giant magnetoresistance biosensor,a current feedback instrument amplifier with chopping technique is designed,which effectively inhibits the influence of low frequency noise and offset on the weak signal to the front end.2.A 12 bit self calibrated SAR ADC is designed.Its features and innovations are that the DAC array uses a piecewise capacitance array based on Vcm,which reduces the power consumption by 87%compared to the traditional DAC capacitor array.At the same time,the bridge capacitance of the segmented capacitor array is integral times of the unit capacitor can enhance matching.Here we employ the calibration of parasitic capacitance to benefits the accuracy of SAR ADC,the structure can decline nonlinear errors.The overall structure improves the accuracy of SAR ADC while reducing the chip area and power consumption.3.Based on the SMIC 0.18 ?m CMOS process,the circuit schematic diagram is built under the Cadence spectre platform,and the supply voltage is 1.8V.By setting the resistor of the current feedback instrument amplifier to control the gain of 80dB,the actual gain is 79.91dB,CMRR is 173.8dB,PSRR is 165.2dB,the PSS+Pnoise simulation is performed on the circuit,the equivalent input noise is 21.85nV/?Hz,the total power consumption is 487.98 ?W,and the value of the noise energy efficiency factor is 39.91,it has good performance.The sampling rate of 12bit SAR ADC is 200KS/s,SFDR is 80.98dB,SNDR is 66.64dB,ENOB of 10.777,and the overall power consumption is 74.98?W.