Comprehensive Analysis of Distortion in the Passive FET Sample-and-Hold Circuit

Analysis simplified with circuit insights reveals the major sources of distortion in a passive FET-switch-based sampling circuit: 1) R_{\mathrm{\scriptscriptstyle ON}} -modulation; 2) turn-OFF-time instant; and 3) signal-dependent charge-injection. Explicit expressions for second- and third-order distortions advance intuitive understanding of the processes of distortion. Circuit simulations and measurement results establish the accuracy of the analysis. Since the three sources of distortion each have a unique dependence on circuit parameters and the input signal frequency, a systematic method is shown to optimize an S/H circuit for least distortion.