The purpose of the sample-and-hold amplifier is to freeze an analog voltage at the instant the HOLD command is issued and make that analog voltage available for an extended period. Figure 8.1 shows various ways of converting three analog input signals to digital signals for acquisition by a single digital n-bit bus.
Figure 8.1: Three schemes for multiplexing several analog
signals down to one digital input path. The notation S/H indicates
sample-and-hold, ADC means analog-to-digital converter, MUX means
multiplexer, and the 
symbol across a line indicates n digital
signals.