Using the Oscillator Probe

The oscillator probe identifies a resonance to be analyzed, and provides initial values used in the frequency calculation. The oscillator probe represents an oscillating voltage source with amplitude given by the parameter A at the frequency given by the parameter FREQ. At all other frequencies, the probe current is zero. The oscillator probe is a frequency domain element; in the time domain (e.g., in transient and DC analyses) the oscillator probe behaves like an open circuit.

The oscillator probe applies a small voltage at a known frequency. Nexxim starts with the frequency specified in the TONES entry in the .OSC statement and also in the FREQ parameter on the oscillator probe, and applies one of several methods to calculate an initial guess at the oscillating frequency. The method used to calculate an initial guess at the circuit oscillating frequency is controlled by the initial_guess option (See Initial Guess for Oscillator Frequency). The voltage given by probe parameter A is always used as the initial probe voltage. The simulator adjusts the frequency and voltage of the probe until both the real and imaginary components of the probe current (I_probe) are zero, that is, Re(I_probe) = 0 and Im(I_probe) = 0. The frequency where this occurs is the oscillating frequency.

Placement of a probe is circuit-dependent. If the focus of the oscillation in the circuit is known in advance, place the probe accordingly. If not, try placing the probe across two nodes in the circuit that exhibits a voltage difference when the circuit is oscillating.