A Low Offset Capacitive Gain Amplifier for High Common Mode Voltage Sense in Battery Management System Application

There is an increasing request for interfacing high input common mode (CM) voltages in voltage or current sense such as battery management system. This paper proposes a capacitive gain amplifier (CGA) designed to sample the differential mode (DM) voltage of signals with a CM voltage that varies from 0 to 90V. A control strategy that integrates chopping and auto zero (AZ) is used to reduce the input offset voltage. This control strategy also accelerates the CM voltage establishment of the CGA. A high-voltage switch (HV Switch) has been designed to ensure that the CM voltage of the input signal reaches 90V, while the DM voltage reaches 5V. A linear trim method is proposed to reduce gain error. The CGA has been manufactured in the DBhitek 0.18-μm CMOS process. As the Vcm varies from 0 to 90V, the circuit has an offset voltage of 3.8μV, an output noise of 71.8nV/Hz1/2 and a gain error of 0.0056%.