Wien Bridge Oscillator

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Jan 20, 2024 03:24 AM
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The Wien Bridge Oscillator is an electronic circuit that can generate a sinusoidal waveform without any input (i.e., it's a type of electronic oscillator). This circuit is notable for its simplicity, low cost, and the ability to produce relatively distortion-free sine waves. Here's a breakdown of how the Wien Bridge Oscillator works:
  1. Basic Composition:
      • The Wien Bridge Oscillator typically consists of an operational amplifier (op-amp) and a frequency-selective RC (resistor-capacitor) network known as the Wien bridge.
      • The Wien bridge network is made up of two RC series legs in parallel. One leg consists of a series-connected resistor and capacitor, while the other leg consists of a series-connected capacitor and resistor.
  1. Frequency Determination:
      • The frequency of oscillation is determined by the RC network. The frequency at which the circuit oscillates is given by:
      • Here, and are the resistance and capacitance values of the components in the Wien bridge. The arrangement of the RC elements causes the network to have a phase shift that varies with frequency.
  1. Feedback Mechanism:
      • The op-amp in the circuit provides the necessary gain and has two feedback paths – a positive (non-inverting) feedback and a negative (inverting) feedback.
      • The positive feedback is taken from the junction of the series RC components, while the negative feedback is usually taken from the op-amp's output.
  1. Oscillation Criteria (Barkhausen Criterion):
      • For sustained oscillations, the circuit must satisfy the Barkhausen stability criterion, which requires the loop gain to be equal to one and the total phase shift around the loop to be an integer multiple of 360 degrees (or 0 degrees modulo 360).
      • In the Wien Bridge Oscillator, the RC network provides a phase shift of 0 degrees at the frequency of oscillation, and the op-amp provides the necessary gain.
  1. Automatic Gain Control:
      • To ensure that the oscillations remain stable in amplitude, some form of automatic gain control is often employed. This could be as simple as a bulb or thermistor in the negative feedback path that varies its resistance with temperature (and thus with signal amplitude), or more complex electronic gain control circuits.
  1. Applications:
      • The Wien Bridge Oscillator is used in a variety of applications where a stable and precise sinusoidal waveform is required, such as in audio equipment, signal generators, and measurement devices.
The Wien Bridge Oscillator is renowned for its good frequency stability and relatively low harmonic distortion, making it a popular choice in applications where these attributes are important.
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