Computation of oscillator open-loop Bode plots

The author presents a method for computing the open-loop gain and phase response of oscillators by using two successive SPICE runs. A current balance method which insures accuracy is described. Some graphical results are discussed, and the difficulties with conventional methods are described. The proposed method introduces a current balance technique which allows a driving signal to be entered into the loop without disturbing the impedance loadings and feedback, and nulls out the unwanted voltage from the measurement of the loop output voltage. The phase slope is related to the loaded Q, which can be used to predict some aspects of the oscillator noise characteristics