Bubba Oscillator
The Bubba Oscillator is a circuit that provides a filtered sine wave of any frequency the user desires based upon the configuration of resistors and capacitors in the circuit. The circuit completes this task with four operational amplifiers that either buffer or amplify the signal. This oscillator is a phase shift oscillator, but unlike other phase shift varieties that require phase shifts of 90 degrees or more, the bubba oscillator only requires a 45 degree shift in order to function. This is because of the four op amps, that when placed in series, produce a total 180° shift.
The bubba oscillator offers a few features that other oscillators cannot, the biggest factor is that the frequency stability holds while still giving a low distortion output. The reason for this involves the four filters that the signal passes through, providing a clear and stable signal at point P5, as shown in Figure 4.