[Premium-Rx] [OT] PLL spurs?

[A. and T. MacDonald]

Hi Brooke,

I've got the past President of TAPR coming over this afternoon to
measure the Phase noise of a board he is building up as a kit project: 

***************
"I just finished a prototype of a simple synthesizer I'm calling
"clock-block" that's based on an ICS525 clock synthesizer chip.  I've
attached a schematic and picture of the prototype (which will need some
layout tweaks before production).

The engineers at ICS warned me that this chip isn't designed for RF
analog applications because it's a wideband VCO with really no loop
filter; it's really designed as a clock replacement, not an LO.

But of course, I'd like to see for myself.  The idea would be to do
phase noise measurements near the top end of the output range, say
200MHz, and down at HF, probably 16MHz because that's the frequency the
datasheet uses for the jitter spec."
**************

I will take a hard look at the spurs today and see if we can't come up
with a few ideas.  It would be nice to have a nice clock source with low
jitter.  The phase noise looks pretty poor on a spec-an.

adam

-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Brooke Clarke
Sent: Sunday, May 14, 2006 12:05 AM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] [OT] PLL spurs?


Hi:

I've recently been working with the ICS525 clock generator IC.  It's a 
PLL on a chip with parallel programmable dividers on the input, on the 
VCO and on the output.  For a little about it see:
http://www.pacificsites.com/~brooke/PRC68COM.shtml#BTSG
An on line calculator is at:
http://www.icst.com/calculators/ics525inputForm.html

When I set the dividers for 400 MHz output with a 16.6666 MHz input the 
spurs are spaced every 16.6 MHz either side of the output.  That's the 
same as the VCO input frequency.  But when the output is 51.0 MHz there 
are spurs every 1.375 kHz but the VCO input is 1.6666 MHz.

ICS says this is not suitable for use as a crystal replacement, probably

for the reason above.  I'm trying to understand if there's a way to 
clean it up.  How can I calculate the spur seperation frequency?

Thanks,

Brooke Clarke



-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com


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