A Low Power Low Noise Two Stage CMOS Operational Amplifier for Biopotential Signal Acquisition System

Monitoring of the biopotential signals in present scenario attract much attention to the researcher due to increasing demand for better quality of life and to enhance interaction between humans and machines. Biopotential signals are relatively weak amplitude and low frequency in nature. Therefore it is required to design a front circuitry that defines quality of signal for processing to the next block (ADC). This paper presents a design procedure by using the Equivalent Circuit Approach (ECA) for a low power, low noise, and rail-to-rail output swing Operational Amplifier (Opamp) which is used at the front end circuitry of Biopotential signal acquisition systems. A differential pMOS input stage is used for noise cancellation and a common source stage is used at the output for high output swing. The opamp is experimentally validated through TSMC 90nm CMOS process Technology and a comparison is carried out with previous designs. This opamp exhibits input referred noise of 28nV/√Hz, Phase Margin =83, B.W=10.1 kHz and power consumption 91μW for 40μA external bias current. Importantly, all these advantages are achieved at the cost of little Gain deviation. Keywords— Biopotential Signal, Equivalent Circuit Approach (ECA), Low noise, Low power, Opamp, Rail-to-rail