SAMPLE-AND-HOLD CIRCUITS2) IC Sample-and-Hold
Because the inverting input terminal of the output op-amp is held close to ground, the voltage across capacitor CF (VC) equals the output voltage (Vo), which is the sampled input voltage (Vi).
When Q1 is on, CF is rapidly charged or discharged to Vi.
When Q1 is switched off, CF holds its voltages.
Feedback keeps the inverting input terminal of the output op-amp close to ground level, so the output is the voltage across the capacitor (VC).
Vo= -Vi = VC
With CF = 1000 pF, the sample acquisition time is typically 4s with an accuracy of 0.1%.
The error due to capacitor discharge between sample periods is defined in terms of a drift rate.
This is the capacitor discharge rate, which is specified as typically 6 mV/s.