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Close switch to start! Okay in this example I'll try to explain the differences and similarities of Amplifiers and Oscillators. This circuit both has characteristics of a differential amplifier and a Phase shift Oscillator.
1. An oscillator is an electronic device that modulates the DC power supply into an AC signal, generated and amplified within its circuitry. Specs like Frequency, Amplitude, Phase and Distortion are solely dependent upon the chosen design and are not generated or controlled by an external source.
2. An amplifier is an electronic device that modulates the DC into AC but with a specific characteristics, defined by an input signal. The only thing an amplifier changes is the amplitude of the signal. The frequency amd form remain intact. Notice the subtle difference? An oscillator is essentially an amplifier but with a frequency determining circuit set within to define the output (LC,RC).
Now a little about feebacks. - So the only distinguishing feature is the feedback type.
- In amplifiers very deep negative feedbacks are employed to ensure low distortion and to prevent oscillations. That means that some of the INVERTED output is taken back to the input, somewhat neutralising the input level. That ensures stability and minimises distortion.
- In Oscillators both Negative and Positive feedbacks are used. A positive feedback means that the output feed is in sync with the input thus causing a normal amplifier to oscillate. The oscillation frequency is determined by a frequency determining circuit (RC,LC). In this particular example the positive feedback is established by the RC filter (↘ part of the circuit). The amplifier provides a 180 degrees phase shift which normally wont kickstart any oscillations but once applied another 180degrees shift by the filter you get a full 360degrees needed for a positive feedback. A certain amount of gain must the amplifier provide to compensate the losses in the RC circuit. An amplitude sensing negative feedback is usually applied to keep the oscillations from rising into cutoff distortion. Such circuit often employs diodes LED's or other types of semiconductors or op amps which tend to activate at a certain level. (<1V for diodes, different for LED's and variable for op amps)
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