**RC Network Oscillators**

Since there is no input, there is no initial current so start-up gain is open-loop. Thermal noise provides initial start-up voltage which quickly multiplies through the op-amp. Since noise is an AC quantity, the output signal is also AC. The frequency of oscillation will increase until Xc = R (resonance) at which it will stabilize. Once resonance is reached, gain will settle to equal one.

**Phase Shift Oscillator**

The inverting input introduces a 180° phase shift; the three RC networks produce another 180° phase shift providing positive feedback (60° each).

Gain must always be approximately 29.

Note that R and C could switch positions; however, that arrangement is know to provide a less "clean" signal.

**Frequency of Oscillation**= resonant frequency for a phase shift oscillator

**Wien-Bridge Oscillator**

Frequency of Oscillation = resonant frequency for a wien-bridge oscillator.

At resonance, the phase shift between the two RC networks = 0°. The gain must be approximately 3.