This paper presents a method to evaluate the performance of high-resol
ution digitizers using signal sources that may be of lower specificati
on than the device under test. The method is based on the best fitting
of a straight line to a set of measures of the signal to noise ratio,
excluding the harmonic distortion, obtained for several amplitudes of
the test signal. Theoretical derivations and both computer simulated
and experimental data are included. It is shown that the effective num
ber of bits estimated using this method is not affected by the leakage
effects that occur when other frequency domain tests are used and the
input signal is sampled along a non-integer number of cycles.