A High Gain and High CMRR Instrumentation Amplifier for Biomedical Applications

Abstract

In this paper, an instrumentation amplifier (IA) based on operational amplifiers (op-amps) for biomedical applications is presented. Such IA achieves high gain and high common-mode rejection ratio (CMRR) while maintaining low power consumption, high power supply rejection ratio (PSRR) as well as other design constraints. The IA uses three identical two-stage telescopic cascode op-amps at the input and output stages. The feedback networks are comprised of resistors and capacitors, which are different from those in conventional voltage mode IA. The resistive feedback is utilized in the input stage to increase the stability while the capacitive feedback is employed in the output stage to filter undesired frequency components and enhance the gain of the IA. The schematic of IA is designed and simulated under 180 nm CMOS technology using Cadence Spectre tool. The gain and CMRR of the single op-amp are 100.45 dB and 94.8 dB respectively. The power consumed by each op-amp is 12.96 $\mu \mathrm{W}$ at a supply voltage of ± 0.9 V. RC Miller compensation technique helps the op-amp reaching a phase margin of 60°. This IA consumes a power of 38.88 $\mu$W and CMRR of 147.68 dB, with a gain of 101.61 dB. The proposed technique is suitable for a variety of biomedical applications due to its high gain and high CMRR.