Sar adc with alternating low and high precision comparators and uneven allocation of redundancy

Abstract

A Successive Approximation Register, SAR, Analog to Digital Converter, ADC, () achieves high speed and accuracy by (1) alternating at least some decisions between sets of comparators having different accuracy and noise characteristics, and (2) unevenly allocating redundancy (in the form of LSBs of range) for successive decisions according to the accuracy/noise of the comparator used for the preceding decision. The redundancy allocation is compensated by the addition of decision cycles. Alternating between different comparators removes the comparator reset time (treset) from the critical path, at least for those decision cycles. The uneven allocation of redundancy—specifically, allocating more redundancy to decision cycles immediately following the use of a lower accuracy/higher noise comparators—compensates for the lower accuracy and prevents the need for larger redundancy (relative to the full-scale range of a decision cycle) later in the ADC process.