The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Measurements >> Phase Noise and Jitter Measurements >> VCO phase noise simulation
https://designers-guide.org/forum/YaBB.pl?num=1151074391

Message started by Molotov on Jun 23^rd, 2006, 7:53am

Title: VCO phase noise simulation
Post by Molotov on Jun 23^rd, 2006, 7:53am

Hello,

I'm using mentor tools to design and simulate different properties and C/C's of VCO.
When i try to simulate the phase noise on ELDO-RF with UMC 0.18u Design Kit, i get strange results:
1) The value of phase noise at 10Hz is over 0dB (actually it reaches 60dB or so)
2) The phase noise shape is somehow strange with the -30 and -20 dB/dec. slopes changed in some points....i realized that its due to the varactor but i want to know if there is a soln. here as the phase noise is degraded so much.

Please if anyone faced any of this reply.

Thanks in advance,
Aboel3la

Title: Re: VCO phase noise simulation
Post by Ken Kundert on Jun 24^th, 2006, 9:31am

See section 4.3 of http://www.designers-guide.org/Theory/cyclo-paper.pdf.

-Ken

Title: Re: VCO phase noise simulation
Post by Molotov on Jun 24^th, 2006, 11:48am

Hello,
Thanks Alot KEN for the reply.
but this actually didn't answer my questions....
I hope for more explanation.
Thx alooot

Title: Re: VCO phase noise simulation
Post by Ken Kundert on Jun 24^th, 2006, 2:18pm

It is hard to answer the question about the strange shape of the phase noise as we cannot see it. Can you post a picture of it?

My response was meant to answer how the noise can be larger than the signal (a noise level of 60dB at 10 Hz would indicate that the noise in the signal contained more power than the signal itself). This is the question I thought you were asking in your first point.

-Ken

Title: Re: VCO phase noise simulation
Post by Molotov on Jun 24^th, 2006, 2:38pm

Thx Alot again KEN.

Your Answer really helped.
about the second point here is a picture of the phase noise....

Title: Re: VCO phase noise simulation
Post by Ken Kundert on Jun 25^th, 2006, 1:26am

That bump at 10 kHz may be due to some time constant in your circuit. Is there a 10 kHz time constant present, perhaps in a bias or supply network?

-Ken