An offset cancellation technique for complementary input buffers

Abstract

ABSTRACTThis article presents an offset cancellation technique suitable for complementary input rail-to-rail operational amplifiers in unity gain buffer configuration that overcomes the variable offset and minimises the increased distortion associated with these circuits. The presented technique is suitable for applications with slow varying input signals compared to the offset sampling frequency and as such is ideal for buffering sigma-delta analogue-to-digital converters. The simulated buffer using the proposed technique exhibits up to 40 dB increase in spurious-free dynamic range and over 30 dB increase in signal-to-noise and distortion ratio. Incorporated in a second-order sigma-delta modulator, simulation results exhibit a 19 dB increase in third-order harmonic distortion. Measurement results verify the technique, illustrating effective offset cancellation regardless of the input signal level.