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Design >> Mixed-Signal Design >> Pls suggest 5GHz VCO for low jitter
https://designers-guide.org/forum/YaBB.pl?num=1141742549

Message started by neoflash on Mar 7^th, 2006, 6:42am

Title: Pls suggest 5GHz VCO for low jitter
Post by neoflash on Mar 7^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?

Title: Re: Pls suggest 5GHz VCO for low jitter
Post by Paul on 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 :(

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

Title: Re: Pls suggest 5GHz VCO for low jitter
Post by neoflash on Mar 7^th, 2006, 5:17pm

Because die size limitation. LC is too big for given die size.

Title: Re: Pls suggest 5GHz VCO for low jitter
Post by huber on 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

Title: Re: Pls suggest 5GHz VCO for low jitter
Post by gitarrelieber on 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.