One useful application to take advantage of the TMUX1121, TMUX1122, and TMUX1123 performance is the sample-and-hold circuit. A sample-and-hold circuit can be useful for an analog to digital converter (ADC) to sample a varying input voltage with improved reliability and stability. It can also be used to store the output samples from a single digital-to-analog converter (DAC) in a multi-output application. A simple sample-and-hold circuit can be realized using an analog switch such as the TMUX1121, TMUX1122, and TMUX1123 analog switches. Figure 9-1 shows a single channel sample-and hold circuit using only 1 of 2 channels in the TMUX112x devices.

Figure 9-1 Single Channel Sample-and-Hold Circuit Example

An optional operational amplifier is used before the switch since buffered DACs typically have limitations in driving capacitive loads. The additional buffer stage is included following the DAC to prevent potential stability problems from driving a large capacitive load.

Ideally, the switch delivers only the input signals to the holding capacitors. However, when the switch gets toggled, some amount of charge also gets transferred to the switch output in the form of charge injection, resulting in a pedestal sampling error. The TMUX1121, TMUX1122, and TMUX1123 switches have excellent charge injection performance of only -1.5pC, making them an excellent choice for minimizing sampling errors in this implementation. The pedestal error voltage is indirectly related to the size of the capacitance on the output, for better precision a larger capacitor is required due to charge injection. Larger capacitance limits the system settling time which may not be acceptable in some applications. Figure 9-2 shows a TMUX112x device configured for a 2-channel sample-and-hold circuit with pedestal error compensation.

Figure 9-2 2-Channel Sample-and-Hold Circuit with Pedestal Error Compensation