A novel approach is presented for digital generation of an analog waveform suitable for BIST of high-resolution analog-to-digital converters (ADCs). The staircase-like exponential waveform is shown to have properties of a perfectly linear ramp when used as the stimulus for a 3rd order polynomial fitting algorithm that measures offset, gain, 2nd and 3rd harmonic distortion. The technique is particularly suitable for testing high resolution (>12 bits) sigma-delta ADCs in a noisy environment, which can then be used to test digital-to-analog converters (DACs). Experimental results for a 44 kHz 16-bit ADC show that the technique measures distortion with better than 0.01% accuracy in the presence of random and 50 or 60 Hz noise.