Dynamic Testing of A/D Converters using the Multiple Coherence Function

A technique to determine the dynamic operating characteristics of multiple A/D converters using the multiple coherence function is presented. The approach is based on well established data processing techniques, namely the Welch modified periodogram spectra estimates and the multiple input/output analysis of Bendat and Piersol. The residual error spectral density, representing the portion of the signal not linearly accounted for by the other channels is interpreted in terms of the quantization noise of the individual devices. The technique is applied to two different multi-channel DAQ cards of different quality and it is shown that the noise characteristics of all the channels can be determined in a single measurement. The technique is shown to work best with white noise inputs but can be applied to a sine wave input if a rectangular data window is used