An Improved Foreground Calibration Method for Capacitor Mismatch in NS-SAR ADC

DAC mismatch is a significant error in NS-SAR ADC. It introduces an essentially nonlinear behavior and causes harmonic distortion of the signal. In this paper, we propose an improved foreground digital calibration method. This method is combined with noise shaping technology, improves calibration accuracy and eliminates the impact of error accumulation on high-bit weights. Thus, it elegantly solves the harmonic distortion caused by the capacitor mismatch. Behavioral simulation of the improved foreground digital calibration method is demonstrated in a 12-bit prototype NS-SAR ADC. As a result, the NS-SAR ADC performance ENOB achieves 17.2bit at 32 x OSR. Compared with conventional foreground calibration method, the SNDR increases from 81.4 dB to 106 dB and the SFDR increases from 86.2 dB to 117.4 dB. A 200-point Monte Carlo simulation demonstrates the robustness of the proposed calibration method.