A Wien bridge oscillator is a type of electronic oscillator circuit that generates a sinusoidal waveform at its output without requiring an external input signal. It's based on a feedback network and uses the concept of negative feedback to sustain oscillations. The primary components of a Wien bridge oscillator are resistors, capacitors, and an operational amplifier (op-amp).
Here's how a Wien bridge oscillator circuit operates:
Basic Components: The Wien bridge oscillator consists of an operational amplifier (op-amp) configured in an inverting amplifier mode, along with a feedback network made up of resistors and capacitors.
Feedback Network: The feedback network consists of two resistors (R1 and R2) and two capacitors (C1 and C2) connected in a specific configuration. The resistors and capacitors are arranged to form a bridge-like structure, which gives the circuit its name.
Frequency-Determining Network: The frequency of oscillation is primarily determined by the values of R1, R2, C1, and C2. The circuit is designed such that the impedance of the feedback network becomes maximum (infinite) at the desired frequency of oscillation.
Phase Shift and Feedback: At the oscillation frequency, the phase shift introduced by the feedback network becomes 180 degrees. This is crucial for the circuit to sustain oscillations. The op-amp, operating in the inverting mode, further introduces an additional 180-degree phase shift. This cumulative 360-degree phase shift around the loop results in positive feedback, which is necessary for sustained oscillation.
Startup: To start the oscillation, some initial disturbance is needed. This can be introduced by noise or by manually perturbing the circuit. Once the initial disturbance is present, the circuit amplifies it, and the feedback mechanism ensures that the oscillations build up until they stabilize.
Amplitude Control: The amplitude of the oscillations can be controlled by adjusting the gain of the op-amp circuit. This can be achieved by varying the ratio of resistors R1 and R2.
Signal Output: The output of the op-amp circuit, taken across the junction of the two resistors (R1 and R2), is a sinusoidal waveform with the frequency determined by the values of the resistors and capacitors in the feedback network.
Sine Wave Distortion: In reality, it's challenging to achieve a perfectly sinusoidal output due to component tolerances and non-idealities in the op-amp. Some level of distortion might be present in the output waveform.
Wien bridge oscillators are commonly used in audio frequency applications where a simple and stable sinusoidal waveform generator is required. However, they have limitations in terms of frequency range and waveform distortion. For higher frequency applications, other types of oscillators like RC oscillators, LC oscillators, or crystal oscillators are often preferred.