Low Voltage Rail-to-Rail Sample and Hold
This low-power circuit will sample signals between 0 and five volts. Settling time is determined not only by R2 but also by the series resistance of the analog switch (about 30 ohms) and the settling time of the OP amps. Holding the sample input high for about 1usec should yield about 0.1% accuracy.
As always, circuits of this type require a high quality, polypropylene hold capacitor for C3. We used a Panasonic ECQ-P1H102GZ.