The quadrature oscillator is another type of phase shift oscillator, where each of the three sections is configured to provide a 90 degree phase shift. The outputs are labeled sine and cosine because they are 90 degrees out of phase, as shown in the figure. The gain of this configuration is calculated by the following formula:
When R1C1 = R2C2 = R3C3 the equation can be reduced to the following form:
When w = 1 / RC the equation is reduced to: 1-180 degrees, which means that the oscillation occurs when = 1 / RC. The circuit used as a test oscillated at 1.65 kHz, a value slightly different from the calculated 1.59 kHz, and the discrepancy was attributed to the variations in component values.
