A Redundancy-Based Background Calibration for Comparator Offset/Threshold and DAC Gain in a Ping-Pong SAR ADC

Abstract

A background calibration algorithm is proposed for comparator offsets and thresholds, and for DAC gains. It leverages redundancy in a 2-step ADC to detect errors without the need for additional analog blocks. The algorithm considers an error to have occurred when the fine phase outputs a result within its redundant range. The detected errors are classified into possible erroneous comparisons, and the source of the error is estimated by analyzing the error occurrence pattern. It has been implemented off-chip for a 4x time-interleaved Ping-Pong SAR ADC, which demonstrates the tolerance for +/- 8% VDD variation and convergence within 180k samples after a sudden 5% VDD drop.