A biopotential amplifier with dynamic capacitor matching for improved CMRR

A technique is proposed for improving the common mode rejection ratio (CMRR) of op-amp based instrumentation amplifiers in resistor–capacitor (RC) feedback configurations. This is done by dynamically matching the input and the feedback capacitor pairs. A fully differential biopotential amplifier was designed with the proposed dynamic capacitor matching (DCM) scheme and its performance compared against the conventional case. The experimental results show that the proposed dynamic capacitor matching technique improves CMRR by more than 40 dB over the conventional case. The proposed technique also reduces the power consumption of the biopotential amplifier. The amplifier consumes less power during the ‘OFF’ periods when using DCM and this results in the overall lower power consumption of the amplifier. The quiescent current consumption of the biopotential amplifier is 20 μA with a 1.5 V dual power supply source and a maximum input referred noise of 3 μV.