SAMPLE-AND-HOLD CIRCUITSCircuit Operation For FET Q1
The waveforms in Fig.7-13(b) illustrate the circuit operation.
V1 must go sufficiently negative to drive the FET gate voltage below its pinch-off voltage (VGS(off)).
V1 should also go to a positive level approximately equal to the capacitor voltage (VC) to ensure complete turn on of the FET.