Loop phase corrections in oscillator feedback networks

Some of the well known oscillator networks have been found to require loop phase corrections so as to oscillate at the reported frequencies. The attenuation of the feedback networks at these frequencies is real while their output impedance is complex. Inclusion in the loop of a real gain amplifier having finite input resistance therefore appears to violate the loop phase condition. The phase discrepancy is very small when the amplifier has large enough input resistance, in which case the circuits oscillate at a frequency slightly different than the reported conventional value. A few oscillator circuits have been designed to specifically highlight these statements. Spice simulation results are in close agreement with those indicated by the circuit analysis. Improved frequency stability of the phase corrected networks is reported.