Amplifier

THEORY

This is the most popular op amp circuit discussed first.

Inverting amplifier

This is the most popular op amp circuit. The polarity of the input voltage get inverted at the output. If a sine wave is fed to the input of the amplifier, output will be amplified sine wave of with 180º phase shift. The gain of the inverting amplifier is given by A= -Rf/Ri , where Rf is the feedback resistance and Ri is the input resistance. It can be used as a scalar as by varying either Rf or Ri, output amplitude can be varied.

Non-inverting amplifier

The circuit provides a gain to the input signal without any change in polarity. Gain is given by A= 1+(Rf/Ri), where Rf is feedback resistance and Ri is the input resistance.

Special case: Voltage follower

It is a non inverting amplifier with unity gain. Here the output voltage is equal to and in phase with the input. So here output follows the input.


PROCEDURE
1. Set up the inverting amplifier as shown in the circuit diagram.
2. Feed a 2 VPP, 50 Hz sinusoidal input and observe the input and output wave forms.
3. Calculate gain A= Vo/Vi.
4. Keep the amplitude of the input constant and vary the input frequency from 50Hz to 2MHz.
5. Measure the output amplitude corresponding to different frequencies and enter it in tabular columns.
6. Plot the frequency response of the circuit.
7. Repeat the procedure for non-inverting amplifier also.