A Wien bridge oscillator is a type of electronic oscillator circuit that generates a sinusoidal waveform at its output without the need for an external input signal. It was invented by Max Wien in 1891 and is commonly used in audio and radio frequency applications. The oscillator's frequency is determined by the values of the components within the circuit.
The basic concept of a Wien bridge oscillator is to create a positive feedback loop with a network of resistors, capacitors, and an active element (typically an operational amplifier, or op-amp). The positive feedback allows the system to sustain oscillations and produce a sinusoidal output.
Here's a simplified explanation of how a Wien bridge oscillator works:
The Bridge Network: The core of the Wien bridge oscillator is a bridge network consisting of two resistors (R1 and R2) and two capacitors (C1 and C2). These components are arranged in a bridge configuration, hence the name "Wien bridge."
Operational Amplifier (Op-Amp): An op-amp is used to amplify the voltage across the bridge network. It plays a crucial role in ensuring that the feedback loop provides the required phase shift for oscillation to occur.
Positive Feedback and Phase Shift: The op-amp is configured to provide positive feedback by connecting the output back to the bridge network through a feedback path. This feedback path involves a voltage divider formed by R3 and R4.
Frequency Determination: The frequency of oscillation is determined by the values of the resistors and capacitors in the bridge network. The bridge network is designed in such a way that the phase shift around the loop is precisely 180 degrees at the desired oscillation frequency. This is important for sustained oscillations.
Start-up and Sustained Oscillations: Initially, there may be some noise or disturbance at the output of the op-amp. However, due to the positive feedback, any signal that is even slightly in-phase with the desired frequency will be amplified and fed back to the input with a 180-degree phase shift. This results in a cumulative buildup of the in-phase signal, while other out-of-phase signals get attenuated. Eventually, the circuit reaches a stable state with sustained oscillations at the desired frequency.
Amplitude Stabilization: The Wien bridge oscillator has an inherent amplitude stabilization property. The gain of the op-amp reduces at higher amplitudes due to its internal limitations, and this helps in maintaining a relatively constant output amplitude.
Output Signal: The output of the oscillator, taken from across the bridge network, is a sinusoidal waveform at the frequency determined by the values of the resistors and capacitors.
It's worth noting that the Wien bridge oscillator is a relatively simple circuit, but achieving precise and stable oscillation can require careful design and component selection. Additionally, the op-amp used in the circuit must have sufficient bandwidth to support the desired frequency of oscillation.