A biopotential amplifier with improved common mode gain

In this paper, a technique is proposed for improving the Common Mode Rejection Ratio (CMRR) of opamp based Instrumentation Amplifiers in resistor-capacitor (RC) feedback configurations by dynamically matching input and feedback capacitor pairs. A fully differential biopotential amplifier is designed with the proposed dynamic element-matching scheme and its performance is compared with the case where dynamic element matching is switched off. Experimental results show that the proposed dynamic element matching technique improves CMRR by over 40 dB over the conventional case. The proposed technique also reduces average power consumption. The biopotential amplifier draws an average of 20uA of quiescent current from a 1.5V dual power supply source. The input referred noise is less than 3uV/sqrt (Hz).