Design of low noise low power two stage CMOS operational amplifier using Equivalent Transistor Replacement Technique for health monitoring applications

The recent interest of mankind on various personal and real time health monitoring system has accelerated the demand for more efficient and advanced biomedical devices. Physiological signals are comparatively weaker in magnitude (few μV to few mV) and also exhibit lower frequencies. Therefore a low power, low input-referred noise analog front end circuitry is to be designed for filtering and amplifying the biopotential signals before digitizing it. A design methodology using the Equivalent Transistor Replacement Technique (ETRT) for low power and low noise Two Stage Operational Amplifier is the front end circuitry of Biopotential Signal Acquisition System. For providing high output swing a Common Source stage is connected at the output and for the reduction of the input-referred noise a differential PMOS input stage is used. The designed circuit of Op-Amp gives a gain of 61 dB, power consumption 60μw, input-referred noise 37nV/sqHz and bandwidth 20.1 KHz for the 60μA external bias current.