Quote:
Originally Posted by Niechcial,Steve
Thanks Tony and G6. The programmable oscillators look fun to play with. I will probably opt though for the crystals> Help much appreciated.
|
Be careful. The 'programmable crystal oscillators contain a phase locked loop with programmable dividers and a VCO.
On-silicon resonators for VCOs are rather limited in the Q they can achieve and this means that the overall phase noise performance they can achieve is much poorer than a straight-forward crystal oscillator alone.
All the counters ackling away on the same die aren't perfectly isolated, so a variety of spurs can be found on the output.
On the plus side, for each different frequency a manufacturer makes for the actual crystal oscillator inside the programmable oscillator package, they can sell them as a large number of frequencies within reach of the VCO's range and the choice of N/M ratios.
Be especially careful because numerous oscillator families in supplier data sheets are now programmable ones. The data sheets often fail to mention thatyou are not getting a simple crystal oscillator.
For noise-critical RF applications, it can be a bit of a devil looking through all the oscillators in stock at a distributor, wondering which ones are quiet.
David