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neoflash Community Fellow Offline Mixed-Signal Designer 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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ywguo

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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 Senior Fellow Offline Posts: 1516 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 Community Fellow Offline Mixed-Signal Designer 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 Community Fellow Offline Mixed-Signal Designer Posts: 397	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 Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 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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neoflash Community Fellow Offline Mixed-Signal Designer Posts: 397	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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