Shared Offset Cancellation and Chopping Techniques to Enhance the Voltage Accuracy of Multi-Amplifier Systems for Feedback Sensing in Power Management Applications

This paper introduces the utilization of two different input-referred offset voltage correction methods applied to multiple amplifiers within a front-end sensing circuit of a buck regulator for the first time. The multi-amplifier system under investigation contains an instrumentation amplifier consisting of three folded cascode stages and an additional amplifier configured as a unity-gain buffer for a reference voltage. The first method in this work alleviates voltage offsets in this 4-amplifier system based on a shared auxiliary amplifier correction circuit that switches between different target amplifiers; whereas the second method applies a chopping-based auto-zero procedure to cancel the input-referred offset voltage of the same amplifiers. Since the instrumentation amplifier is designed for feedback sensing in integrated power management applications, it has a relatively high bandwidth requirement. For this reason, the chopping technique does not involve a low-pass or band-pass filter. Instead, a successive approximation register (SAR) analog-to-digital converter is used to sense the output. Measurements of the amplifiers fabricated in a 130nm CMOS technology demonstrate that the auxiliary auto-zero offset cancellation method leads to lower input-referred offset voltage standard deviation ( $\sigma = 1.31\,\,\mu \text{V}$ ) compared to the chopping technique ( $\sigma = 184.67\,\,\mu \text{V}$ ), and that the die area requirement and power consumption with the auxiliary amplifier-based offset cancellation (0.105 mm ² , 1.32 mW) are lower than with the chopping method (0.25 mm ² , 1.72 mW).