The Design Of Low Power CMOS Analog Front End For Weak Biological Signal Detection

In recent years,with the development of the medical equipment and integrated circuit technology,as a cross discipline of the two subjects,the design of the biomedical chip has become a hot research topic in the field of integrated circuits.CMOS analog front-end circuit is an important part of biological signal detection system,and its main functions are to pre amplify,adjust and transform the weak biological signal.The performance of CMOS analog front-end circuit directly determines whether the target signal can be accurately extracted,so its in-depth study has great significance on the field of biomedical chip.According to the research of system architecture and key technology of the low power analog front end of weak signal detection circuit,this paper designs low power CMOS analog front-end integrated circuit that can detect weak electrocardiosignal(ECG)and electroencephalogram(EEG)signals.The domestic research of front-end circuit for biological signal detection was little at present.Based on analyzing characteristics of ECG and EEG,this paper introduced a low power CMOS analog front-end integrated circuit for weak signal detection.The whole analog front-end integrated circuit system contained low noise operational amplifier,programmable gain amplifier with switching capacitor,successive approximation analog to digital converter(SAR ADC)and other modules.Instead of the traditional instrumentation amplifier,low noise amplifier used fully differential Rail-to-Rail operational amplifier as the main structure,and achieved rail to rail common mode input range,improved the utilization rate of the power supply,realized low noise characteristics by chopper modulation technique.This low noise amplifier had lots of advantages such as low process requirements,simple structure,low power.Programmable gain amplifier used differential folded cascode operational amplifier and switch capacitor network to achieve four adjustable gain and used the subthreshold bias technique to achieve low power consumption.In addition,compared with the traditional front-end circuit,this paper increased on-chip SAR ADC to change the shortcoming of analog output existing in the front-end circuit nowadays.SAR ADC adopted 12 bit fully differential structure while DAC used piecewise capacitor structure,comparator adopted a dynamic comparator structure with a pre-amplifier circuit,in the pre-amplifier circuit a positive feedback load structure and subthreshold technique are adopted to realize the low power consumption characteristics.The sleep control signal,Sleep,was also added in this module to make ADC change into resting state after conversion in order to reduce the static power of the circuit.With the properties of simple structure,low power consumption and digital output,the circuit could be used for a variety of biomedical signal acquisition.CMOS analog front-end Integrated circuit introduced in this paper adopted GSMC 0.18 um standard CMOS technology,in which the power supply voltage was 1.8V,and the simulation were completed by Cadence Spectre.The simulation results showed that for the analog front-end weak signal amplification circuit,the power consumption was 73.2?W and had rail-to-rail common mode input range.As for SAR ADC,the effective number of bits reached11.31,the power consumption was 42.4?W.The whole power consumption of front-end circuit was 115.6?W,and the circuit could achieve accurate digital output.The theoretical research of this paper has significance to the development of front-end chip in biological signal detection field.The completed design of low power analog front-end CMOS circuit for weak signal detection has important application value and broad application prospect.