Generating a waveform having one signal level periodically and different
signal levels in other durations. Two input signals are received, one having a
desired constant level and another having desired signal levels. The desired output
waveform is generated by selecting one of the two input signals. As a result, the
output waveform may be generated to have (transitions) with high frequency even
if the signal levels between adjacent portions are substantially different. Such
waveforms are useful to test CDS (correlated double sampling) samplers.
