Lpc2000

--- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@...> 
wrote:
>
> At 01:12 AM 4/4/2006 +0000, unity0724 wrote:
> >Some opinions needed:
> >If I'm running CPU clock at 18MHz with an external 18MHz crystal,
> >which is more reliable (over full temperature/voltage range):
> >-  Switch off the PLL (clock source from external crystal/OSC)
> >-  Turn on 1x PLL  (Clock source from PLL VCO/CCO)
> 
> The PLL almost certainly can't be more reliable than the 
> oscillator since it uses the oscillator as an input. I'd just 
> use the oscillator and leave the PLL off.  You do gain in 
> having a simpler circuit and marginally simpler software
> but I doubt it makes a great deal of difference in 
> reliability.  More noticeable would be a reduction in power 
> requirements and perhaps EMI.
> 
> On the other hand unless there is a real difference in 
> reliability why bother with the PLL
> 
> Robert
> 

Umm... Somehow I thought of PLL/VCO with low pass filter might:
- Reject any noise, glitch, short pulses on the oscillator
  (e.g.,  there might be a surge/lightning nearby affecting the 
   OSC, but not the PLL)
- PLL/VCO gives 50% duty cycle clock to CPU
Any idea which clock source is more stable??
Regards