A Chopper Instrumentation Amplifier With Input Resistance Boosting by Means of Synchronous Dynamic Element Matching

In this work, we propose a method to increase the parasitic input resistance caused by application of chopper modulation to indirect current feedback instrumentation amplifiers. The result is obtained by applying dynamic element matching to the input and feedback ports at the same frequency as chopper modulation. The proposed approach requires effective offset ripple rejection and equalization of the input and feedback common mode voltages. An in-amp architecture that meets both requirements and embodies the proposed input resistance boosting method is described. Experimental verification is provided by means of a prototype designed and fabricated using the 0.32 μm CMOS devices of the STMicroelectronics BCD6s process. The amplifier operates with a 3.3 V supply voltage and a total current absorption of 170 μA. An input impedance in excess of 1 GQ has been measured at a chopper frequency of 20 kHz. The input referred voltage noise density is 18 nV/sqrt(Hz) with a flicker corner of 0.2 Hz and 200 Hz bandwidth.