When perturbed, the oscillator responds by spiraling back into the limit cycle, but not necessarily at the same phase.
Therefore, as Δf → 0 the PSD of v flattens out, as shown in Figure 3(removed due to unknown copyright status).
The voltage noise Sv is considered to be a small signal outside the linewidth and thus can be accurately predicted using small-signal analyses.
With driven cyclostationary systems that have a stable time reference, the correlation in frequency is a series of impulse functions separated by fo = 1/T.
If the time-of-flight is long enough, the phase difference between the two becomes completely randomized and the two signals can be treated as if they are non-synchronous.
If the time-of-flight is very short, then there is no time for the phase difference between the two to become randomized and the noise is treated as if it is simply cyclostationary.
In this case, one must be careful to take into account the smearing in the correlation spectrum that occurs with oscillators.