A Wien Bridge Oscillator is an electronic circuit that generates a sinusoidal AC waveform at its output. It is based on the principle of a feedback network that provides the necessary phase shift and amplitude control to sustain oscillations.
Here's how a Wien Bridge Oscillator generates a sinusoidal AC waveform:
Basic Oscillator Configuration:
The Wien Bridge Oscillator consists of an amplifier with positive feedback, which is essential for generating oscillations. The amplifier could be an operational amplifier (op-amp) or a transistor-based amplifier.
Feedback Network:
The key component of the Wien Bridge Oscillator is the feedback network, which is typically composed of resistors and capacitors arranged in a specific configuration. The basic components of the feedback network are two resistors (R) and two capacitors (C).
Frequency-Determining Network:
The combination of the resistors and capacitors in the feedback network determines the frequency of oscillation. The network is designed to provide a phase shift of 180 degrees at a particular frequency (f) known as the oscillation frequency or the Barkhausen criterion frequency.
Phase Shift and Feedback:
At the oscillation frequency (f), the feedback network provides a 180-degree phase shift. This means that the output signal and the input signal at the amplifier's non-inverting input are 180 degrees out of phase. The positive feedback from the output to the input causes the circuit to start oscillating.
Amplitude Control:
The Wien Bridge Oscillator has inherent amplitude control due to the reactive components (capacitors) in the feedback network. When the amplitude of the output signal increases beyond a certain point, the nonlinearity of the amplifier or the reactive elements will limit the signal's growth, preventing runaway amplitudes.
Oscillation Start-up:
To initiate the oscillations, there must be some initial noise or disturbance in the circuit. Once the feedback network provides the required 180-degree phase shift at the specified frequency, the oscillator will sustain oscillations at that frequency.
Frequency Stability:
The stability of the oscillation frequency is primarily determined by the accuracy and stability of the resistors and capacitors used in the feedback network. Any changes in these components' values can lead to variations in the oscillation frequency.
Overall, the Wien Bridge Oscillator's feedback network, designed to provide a 180-degree phase shift at a specific frequency, allows the circuit to generate and sustain sinusoidal AC waveforms at that frequency. By adjusting the values of the resistors and capacitors, the oscillation frequency can be tuned to the desired value.