Do VCXOs have better phase noise and jitter performance than VCOs?
It depends. Different devices have different close-in versus wideband phase noise. Often, this is an observable difference between VCOs and VCXOs. However, an important difference between the two is that VCOs typically have much higher gain (Kvco) than VCXOs. VCXOs usually have a very narrow tuning range. This allows for much narrower loop bandwidth to be easily attained, and therefore better close-in phase noise performance. VCOs, on the other hand, tend to have a lower wideband noise floor. In both cases, this wideband phase noise can be filtered with bandpass filters thereby yielding a lower total jitter.
