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XOSC jitter

A

Andrew Holme

Jan 1, 1970
0
I've got a 10 MHz crystal oscillator :

http://www.iqdfrequencyproducts.com/products/details/181/

mounted on FR4 and phase-locked to an external standard.

Triggering my 'scope off the external standard, at 1ns per cm, I can see
some very low frequency jitter on the XOSC output. If I tap the XOSC or
even just press on the board around it, the XOSC output edge moves hundreds
of ps!

My PLL loop bandwidth is only ~ 1 Hz and it looks like I need to increase it
by an order of magnitude at least to reduce this jitter; but I'm shocked
that the XOSC is so microphonic!

Is this normal?
 
A

Andrew Holme

Jan 1, 1970
0
Andrew Holme said:
I've got a 10 MHz crystal oscillator :

http://www.iqdfrequencyproducts.com/products/details/181/

mounted on FR4 and phase-locked to an external standard.

Triggering my 'scope off the external standard, at 1ns per cm, I can see
some very low frequency jitter on the XOSC output. If I tap the XOSC or
even just press on the board around it, the XOSC output edge moves
hundreds of ps!

My PLL loop bandwidth is only ~ 1 Hz and it looks like I need to increase
it by an order of magnitude at least to reduce this jitter; but I'm
shocked that the XOSC is so microphonic!

Is this normal?

I meant to say mounted on 1.6mm FR4 i.e. quite flexible. I've just checked
a second board and it's doing exactly the same thing. Looking at the
(AD9901-style) PFD output, the edge due to the external standard is rock
solid; but the edge due to the XOSC is all over the place. Phase noise at
high offsets looks fine on the spec an; but ultra close-in looks quite bad
when viewed as jitter in the time domain.
 
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