Subject: Liner Integrated Circuits

Topic: Non-Linear Applications of Operational Amplifier

Difficulty: Medium

RC Phase Shift Oscillator

A 3-stage RC Phase Shift Oscillator is required to produce an oscillation frequency of 10 kHz.

R = 0.065 / (fo x C)

Assume C = 3.3nF
R = 0.065 / (10K x 3.3nF)
=1.96K
= 2K (standard)

To prevent the loading of the amplifier because of RC networks, it is necessary that R1 >= 10 R.
therefore R1 = 20K

Since the resistor-capacitor combination in the RC Oscillator circuit also acts as an attenuator producing a total attenuation of -1/29th ( Vo/Vi = β ) across the three stages, the voltage gain of the amplifier must be sufficiently high enough to overcome these RC losses

Av >29
Av = Rf / R1

if R1 = 20K
Rf = 29 x 20K
= 580K