> You've talked about "pull" a lot but that's only part of the picture.  I
> can imagine at least 3 key specifications:
>
> Pull-- If the control voltage is varied from minimum to maximum, how much
> does the frequency change?
>

This is very important in our application.  If unable to vary frequency
enough, a lock is unattainable.  This translates to either a "muted"
signal, or full-blown digital noise.

> Accuracy-- If a particular control voltage is applied, how close is the
> frequency to the expected value?
>

It doesn't really matter (to an extent) because the osc. is being used to
lock onto an existing clock.  It is not being used as an absolute
"reference" persay.

> Stability-- With the control voltage held constant, how much does the
> frequency change due to other factors?  Poor stability of course implies
> poor accuracy.
>

Again, as long as the circuit continues to oscillate, it's okay.

> If you need a circuit with large pull and high accuracy, it's going to be
> expensive.  Most likely you don't, especially if a constant input signal
> is present that your circuit can phase or frequency lock to.
>

That is correct.  But because there are many input sources to choose from,
high pull IS necessary, as accuracy and stability are not so important.

<SNIP>

>
> Without knowing about your application, I couldn't say if various
> "hybrid" techniques could be used.  For example, an oscillator with poor
> accuracy could be periodically re-calibrated to a fixed crystal
> oscillator.  Or the pull of an oscillator could be increased by using
> digital techniques to modify the output frequency.  A "pretty good
> feedback circuit" can be very useful.  Feedback can make many
> "impossible" things possible.
>

Could you elaborate on the former hybrid?

-Vince

>
>
>
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