RC Phase shift oscillator using Op-Amp
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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
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 Ï€ 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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