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neoflash Community Fellow Offline Mixed-Signal Designer Posts: 397	Pls suggest 5GHz VCO for low jitter Mar 07^th, 2006, 6:42am I am working on a 5GHz 130nm VCO, however, low jitter requirement drive me mad. (<2ps rms). And I am limited to ring oscillators, any siggestion?
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Paul

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Switzerland

Re: Pls suggest 5GHz VCO for low jitter
Reply #1 - Mar 7^th, 2006, 12:04pm

Hi,

I'm not 100% sure, but this jitter requirement seems very tough to realize in 130nm CMOS... Don't forget that each driver stage you add at the clock output also adds jitter, so your oscillator should even be better than your spec. For illustration purpose, 2ps_RMS is current state-of-the-art for high-performance oscilloscope time bases, which usually use SiGe components Sad

In any case, don't forget to put the oscillator on a separate regulated power supply to minimize additional noise due to limited PSRR. Possibly a single-ended topology has less device noise sources and may improve the overall noise, but of course it has other issues like substrate and supply sensitivity...

May I ask why you are limited to ring oscillator topologies if the jitter specs are so stringent?

Good luck

Paul

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neoflash Community Fellow Offline Mixed-Signal Designer Posts: 397	Re: Pls suggest 5GHz VCO for low jitter Reply #2 - Mar 7^th, 2006, 5:17pm Because die size limitation. LC is too big for given die size.
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huber

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GO BEARS!

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Los Angeles

Re: Pls suggest 5GHz VCO for low jitter
Reply #3 - Mar 13^th, 2006, 10:29am

I think this jitter spec might be unrealistic for a ring oscillator. If you insist on trying, inverter-based delay cells
should give lower jitter than differential delay cells for the same power dissipation. Try this reference:

Abidi, A.A.; Samadian, S., "Phase noise in inverter-based & differential CMOS ring oscillators," Custom Integrated Circuits Conference, 2005. Proceedings of the IEEE 2005 , vol., no.pp. 450- 453, 18-21 Sept. 2005

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gitarrelieber Junior Member Offline Posts: 12 Villach	Re: Pls suggest 5GHz VCO for low jitter Reply #4 - Apr 6^th, 2006, 8:33am LC VCO is not necessarily large in size. Especially, if the oscillation frequency is 5GHz, the L and C are relatively small. I think the tuning range will be a problem if you use LC VCO. And LC-VCO is normally difficult to design due to the on-chip spiral inductor which is normally not well characterized.
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