Selecting test frequencies for sinewave tests of ADCs

It is well known that if the frequency used for a sinewave test of an analog to digital converter or waveform recorder is strategically chosen, it is guaranteed that the phases of the samples will be uniformly distributed between 0 and 2π. The requirement is that the record contain an integer number, J, of cycles and that J is relatively prime to the record length, M. We analyze how the sample uniformity is affected by small changes in J from its integer value. It is shown that the behavior depends on the value of K, the multiplicative inverse of J Mod M, and that the behavior can be drastically different for positive and negative errors in J. We provide tables of particularly good values for J for both positive and negative errors. We provide a strategy for selecting the values of M and J and for controlling the sign of the frequency error.