Parallel pipelined calculation of two calibration values during the prior conversion cycle in a successive-approximation-register analog-to-digital converter (sar-adc)

Abstract

A Successive-Approximation Register Analog-to-Digital Converter (SAR-ADC) predicts compensation values for use in a future cycle. A compensation value is applied to capacitors in a calibration Y-side capacitor array to compensate for capacitance errors in a binary-weighted X-side capacitor array. Two compute engines pre-calculate predicted-0 and predicted-1 compensation values for a next bit to be converted. At the end of the current cycle when the comparator determines the current bit, the comparator also controls a mux to select one of the two predicted compensation values. Thus the compensation value is available at the beginning of the next bit's cycle, eliminating a long calculation delay. The compensation value for the first bit to be converted, such as the MSB, is calculated during calibration. Compensation values for other bits are data-dependent. Calibration values are accumulated during calibration to generate the first conversion compensation value for the first bit to be converted.