Feedback is the same as a conventional op-amp voltage follower which yields 11 unity-gain, noninverting output. This hookup also has a very high input impedance. The only difference between a track-and-hold and a sample-and-hold is the time period during which the switch is closed. In trackand- hold operation,
the switch is closed for a relatively long period; the output signal might change appreciably and would hold the level present at the instant the switch is opened. ln sample-and-hold operation, the switch is closed only for the time necessary to fully charge the holding capacitor.