INTERSTAGE GAIN PRORATION TECHNIQUE FOR DIGITAL-DOMAIN MULTISTEP ADC CALIBRATION

The interstage gain proration technique greatly simplifies the task of digitally calibrating multi-step analog-to-digital converters (ADC's) by reducing the number of error measurements and the memory size to s tore code errors. This technique also makes it feasible to move the ca libration hardware into the digital domain, leaving only the switching function in the analog domain. Even though calibrating a multi-step A DC stage-by-stage gives rise to a range mismatch problem between stage s, by digitally subtracting prorated interstage gain errors from the l atter-stage code errors, the proposed technique corrects nonlinearitie s resulting from these inaccurate intrstage gains. Simulated ADC examp les based on a capacitor-array (C-array) multiplying digital-to-analog converter (MDAC) demonstrate a substantial saving in the number of co de-error measurements. For example, when calibrating two stages of n1 and n2 bits each, the resulting number of code-error measurements is 2 n1-1 +2n2 in comparison to 2n1+n2-1 of the straightforward single-stag e calibration.