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Low Jitter Clock Generation with a External Crystal (Read 4172 times)
neoflash
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Posts: 397
Low Jitter Clock Generation with a External Crystal
Oct 19
th
, 2009, 11:56am
Hi folks:
We are leaning to design a clock generator with a external crystal.
Pierce and Colpitts oscillator seems to dominate the design. Which type better suites our target and why?
Regards,
Neo
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Last Edit: Oct 20
th
, 2009, 9:02am by neoflash
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ywguo
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Shanghai, PRC
Re: Low Jitter Clock Generation with a External Crystal
Reply #1 -
Oct 20
th
, 2009, 8:26pm
neoflash wrote
on Oct 19
th
, 2009, 11:56am:
Hi folks:
We are leaning to design a clock generator with a external crystal.
Pierce and Colpitts oscillator seems to dominate the design. Which type better suites our target and why?
Regards,
Neo
Neo, what is your target? It is vague to say design a clock generator.
What is the clock frequency?
Any requirement on phase noise or jitter?
How many pads are available?
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raja.cedt
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Germany
Re: Low Jitter Clock Generation with a External Crystal
Reply #2 -
Oct 20
th
, 2009, 9:17pm
hi Neo,
if you are able to design colpits oscillator with your specifications then from many points of view it is the best one (like excellent phase noise, frequency stability..etc)
Thanks,
rajasekhar.
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neoflash
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Posts: 397
Re: Low Jitter Clock Generation with a External Crystal
Reply #3 -
Oct 21
st
, 2009, 6:20am
We need a low jitter ~50MHz clock generator. Sub-picosecond is the target when applied with a 10MHz HPF.
Currently, the confusion is that the same device gm can not startup colpitts while having no problem with Pierce.
Two pads is possible.
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neoflash
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Re: Low Jitter Clock Generation with a External Crystal
Reply #4 -
Oct 21
st
, 2009, 12:24pm
I did some analysis and found that pierce and colpitts are exactly same in small signal.
More confused why Colpitts doesn't start while pierce always start easily.
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loose-electron
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San Diego California
Re: Low Jitter Clock Generation with a External Crystal
Reply #5 -
Oct 21
st
, 2009, 5:49pm
there is a dialog here on the fourum about "quick starting crystal" oscillators and some simulation tricks - search for it, some useful things there, because High Q crystals often get messed up in simulation.
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Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical
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neoflash
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Re: Low Jitter Clock Generation with a External Crystal
Reply #6 -
Oct 21
st
, 2009, 8:33pm
Just realized that body effect in Colpitts has to be removed. Otherwise, the complete small signal negative resistance change.
Stupid mistake and ignorance.
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