High precision bidirectional chopper amplifier with extended common mode input voltage range

This paper presents a chopper amplifier for precision current sensing, capable of handling common mode input voltages outside the supply rails. For high common mode rejection ratio (CMRR) and DC gain, the amplifier employs a three-stage topology with nested-Miller frequency compensation. By using the chopping technique, a referred to input offset voltage of ±90μV is obtained. To reduce the output ripples caused by the chopping technique the amplifier employs a notch filter. A CMRR of 123dB has been obtained, considering a supply voltage of 5V, for a common mode input voltage range from 4V to 80V. The stability of the operational amplifier (OA) is ensured for a minimum closed loop gain of 20V/V.