RC Phase shift oscillator using Op-Amp

 

Welcome again. This time we have a new topic name- [ RC Phase shift oscillator using Op-Amp ] 

So let us know more about this topic. This is an oscillator; by hearing the oscillator's word, it sounds like something about oscillations. For proper understanding, we should go with its definition

              [An oscillator is an electronic or mechanical device that produces regular oscillations in the form of electrical or mechanical energy. ] 

According to the above simple definition, oscillation can be electrical and mechanical. Therefore, we are going to see electrical oscillation or oscillator. 

Now we know what an oscillator is. 

We will just study one of its specific types of RC phase shift oscillator, in this topic. 

Why it is called RC phase shift? 

It is called RC phase shift because it uses a network of resistors(R) and capacitors(C) in their circuit, performing significant roll phase shifting. In this circuit, we are using an RC network to provide a phase shift; this is called an RC phase shift.

And we are also using Op-Amp for the oscillator circuit.

RC Network:

In the RC network, we use three stages of RC; each RC network is designed to introduce a phase shift of 60º precisely at the desired frequency of oscillations. 

Thus the total phase shift introduced by the three-stage RC network is 180º. The RC network is sometimes called the loader network. It produces a phase shift of 180º precisely only at a particular frequency which is the operation of the oscillator.

Operational amplifier(Op - Amp)

An operational amplifier (op-amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output.

 The op-amp is used as an inverting amplifier; therefore, it introduces a phase shift of 180º between input and output.

Circuit Diagram 

This circuit diagram is designed through EasyEDA online editor.

Simulation

Here is a simulation of the circuit simulation, go through this simulation for a better understanding and get an idea about this circuit works.

For the simulation, page click here.

Output signal

Operation of the circuit

The op-amp is used as an inverting amplifier. Therefore it introduces a phase shift of 180º between its input and output.

The output of the inverting amplifier is applied at the input to the RC phase shift network. As discussed earlier, this network will introduce a phase shift of 180º. So by adding both phase shifts then we will get a 360º or 0º phase shift, which is necessary for oscillations. This feedback network attenuates the signal at its input and feeds it to the amplifier input. The level of attenuation is decided by the feedback factor β.

The gain of the inverting amplifier is decided by the values of Rf and R1. The gain is adjusted so that the product |Aβ| is slightly greater than 1.

The expression for the frequency of oscillations of an RC phase shift oscillator using OP - AMP is given by

f= 1/ (2 π R C √ 6)

Applications:

• Low and medium frequency sin wave generators.
• Function generators/signal generators are used in laboratories.
• Variable frequency signal generators.

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