crystal oscillator selection for PLL design

[liusupeng]

I noticed that for PLL designs presented in papers, they are all using crystal oscillator about 26MHz or close to it. what are the reasons for this?

 

[edpalmer42]

I noticed that for PLL designs presented in papers, they are all using crystal oscillator about 26MHz or close to it. what are the reasons for this?

It's just coincidence that you happened to find some papers that used oscillators in the 26 MHz range. You can phase lock any oscillator, not just a crystal oscillator, that has a voltage control input. Your choice of frequency is determined by the input frequency, the desired output frequency, and the ratios between them. I was recently experimenting with phase locking a yig oscillator at 6.8 GHz to a synthesized generator at 680 MHz via a harmonic mixer. It worked, but my crude circuit was too noisy for my application.

Ed