Calibration technique for time-interleaved analog-to-digital converters

Abstract

A reference analog-to-digital converter (ADC) samples an input signal in parallel with sub-converters of a time-interleaved ADC. For each sub converter and for each of a plurality of output samples from the sub-converter, a calibration circuit determines whether the output sample from the sub-converter indicates an input signal polarity opposite that indicated by the reference ADC. For each such instance, a DC-offset sample is calculated as a difference between the output sample from the sub-converter and a target zero-crossing value for the sub-converter output. For each sub-converter, a series of DC-offset samples is filtered, to produce an average zero-crossing error for each sub-converter. This filtering may comprise a simple average, for example, or a moving average, a decaying filter, etc. Finally, a zero-crossing correction is applied for each of one or more of the sub-converters, based on the respective average zero-crossing error.