A Current-Feedback Instrumentation Amplifier With a Gain Error Reduction Loop and 0.06% Untrimmed Gain Error

This paper presents a power-efficient current-feedback instrumentation amplifier (CFIA) with high gain accuracy. It is intended for interfacing precision bridge transducers and thermocouples that output mV-level signals. The gain accuracy of the CFIA is mainly limited by the mismatch of two transconductors. Applying dynamic element matching (DEM) to them ensures good gain accuracy, gain drift, and linearity. As a result, these transconductors can be implemented as simple differential pairs, resulting in significantly improved power efficiency when compared with the use of resistor-degenerated stages. To suppress the output ripple caused by DEM, an automatic gain error reduction loop dynamically nulls the G_m mismatch of the input and feedback transconductors, thus eliminating the need for trimming. The prototype chip was realized in a 0.7-μm CMOS process. Measurement results show a maximum 0.06% untrimmed gain error and a 5-ppm INL at a gain of 100. This work also achieves an NEF of 11.2, a maximum input-referred offset of 3 μV, and a CMRR of 127 dB while consuming only 290 μA at a 5-V supply.