Noise Analysis of Current-Feedback DC-Servo Loop in Current-Balancing Chopper Amplifiers

Chopper amplifiers for biopotential acquisition commonly suppress differential electrode DC offsets by using a DC-servo loop (DSL). However, the noise contribution of the DSL is always neglected in noise analysis. The noise introduced by the DSL, in particular at low frequencies, is of great importance in biosensor applications. This work presents the noise modeling of a current-balancing chopper amplifier with DSL and describes the effect of the DSL on the noise performance. Two different DSL implementations are analyzed. It is found that the exact placement of the chopper in the DSL has a strong impact in the noise performance; therefore, its placement can not be arbitrarily selected. A circuit topology to minimize its noise contribution is then proposed and verified by simulation.