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Amplitude of Xtal in to IC

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mg9

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Hello, I'm not sure if this is OK or not::confused:
I'm using PIC18F2450, and there's a xtal at Timer1. The amplitude at Timer1 input is typically 800mV, and at it worst case(temp change) can be at 500mV. Is this normal? Although it still can function properly, but I just worry this low amplitude, wouldn't it much more susceptible to noise or something like ESD? Anyway to increase? Change IC?:eek:

Normally, an oscillator circuit is check on load capacitance, start up timing, drive level, oscillator margin(-ve rst), right? Did i miss out anyth else?
 

hjames

New Member
Crystals are essentially filters, so you should see a nice sine wave coming out of it. 500mV sounds okay - if you can see nice big cmos level signals on the PIC's drive pin/xtal2 pin, it's probably okay.

Load capacitances usually end up causing frequency errors exceeding the 100ppm tolerances, but that's about it. If the drive level is set to drive a tuning fork/32KHz crystal with a drive strength meant for a high speed xtal, it might damage the xtal, but that's pretty much the only case.

If you're really paranoid, check the voltage extremes and make sure the area around the crystal is clean/residue free. Do an actual accuracy test if you need to - and tune the capacitances, accounting for the trace and pin parasitic capacitances. Make sure the load caps have good short ground connections, and if you have a metal case crystal, check to make sure it can't accidentally short itself - may need some plastic insulators. That's about it though.
 
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