85.1 Digital Processing of Continuous-Time Signals .. Since the ad conversion takes a finite amount of time, a sample-and-hold(s/h) circuit is used to ensure that the analog signal at the input of the a/D converter remains constant in amplitude until the conversion is complete to minimize the error in its representation§5.1 Digital Processing of Continuous-Time Signals • Since the A/D conversion takes a finite amount of time, a sample-and-hold (S/H) circuit is used to ensure that the analog signal at the input of the A/D converter remains constant in amplitude until the conversion is complete to minimize the error in its representation