3 R value resistors are connected in the opamp circuit in the figure. One of the resistors is variable and T is used to express the resistor value that the potentiometer is divided at any moment. Derive the expression that gives the output voltage Vo.
Output of an inverting amplifier is given by
Output of a non-inverting amplifier is given by
where, is the feedback resistor connected from the output to the inverting input of the Op-amp.
This given circuit is also know as a Switch-hitter.
The wiper of a potentiometer is the channel through which the signal is taken to the non-inverting input of the Op-amp.
The potentiometer resistance from the wiper to the ground is given by
Now, by using the voltage division rule, voltage at the non-inverting op-amp input is given by:
Redrawing the circuit and showing separately the sources driving the two input terminals of the Op-amp-
By Superposition theorem-
Output due to signal present at only non-inverting input, is given by-
And output due to signal present at just inverting input, is given by-
So, by superposition of the two sources, output voltage is given by-
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