Opamp voltage follower,sample and hold circuit

Voltage follower

Voltage follower is one in which the output exactly follows the input. The circuit shown below acts as ideal DC voltage follower.

voltage follower

voltage follower

The output exactly follows the input because the two inputs are tied together virtually, hence Vout = Vin.

Sample and hold circuit

The sample and hold circuit using op amp is shown below

sample and hold circuit using Op amp

sample and hold circuit using Op amp

The switching element will be a electronic device such as MOSFET with control voltage applied to gate consisting of a train of pulses. Whenever the switch is closed i.e. MOSFET is on, the capacitor charges to the voltage at the input with a time constant equal to on resistance of control device *C. After the switch is opened (MOSFET is off) the capacitor holds the charge and hence the voltage across capacitor cannot change since it does not have any path to discharge. Then the voltage across the capacitor is replicated at the output by a voltage follower.

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