Low cost dynamic error detection in linearity testing of SAR ADCs

Abstract

High resolution ADCs employing histogram test for linearity measurement suffer from high test time. This test time is an important factor in determining the overall cost of the ADC. While alternate test methods for linearity checks in the presence of static errors have been proposed, no low cost test method for the detection of dynamic errors has been reported so far. This paper analyzes dynamic errors in SAR ADCs and proposes a test method to detect these errors. This algorithm, when combined with the previously reported uSMILE (ultra fast segmented model identification of linearity errors), gives better noise averaging capability than the conventional histogram test. By applying constrained polynomial fit technique over strategic points in the reduced hits per code histogram data, we are able to suppress the effect of noise in the histogram test and thus, accurately detect dynamic errors. Results on a sample set of 50 devices of a 12 bit ADC indicate an excellent match between the sine histogram test with 240 hits per code for linearity measurement and the proposed method with just 4 hits per code.