The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> noise folding in VCO https://designers-guide.org/forum/YaBB.pl?num=1166309990 Message started by chenyan on Dec 16th, 2006, 2:59pm |
Title: noise folding in VCO Post by chenyan on Dec 16th, 2006, 2:59pm According to my calculation and also other publications. The noise contribution of differential pair to VCO phase noise doesnot change with W/L if Gm of this pair considered a square wave-like. But in spectreRF simulation, the noise V^2/Hz decreases when W/L is inreased. My simulation was always in current-limted region a square-wave like Iout. Also the frequency changes from parasitics of the transistors are compensated with ideal caps so all the simulations oscillate at same freq. Tail current is also kept same therefore a almost same vout amplitude. Does anyone know why? Thanks |
Title: Re: noise folding in VCO Post by sheldon on Dec 16th, 2006, 3:13pm Chen, Could you provide the reference you are referring to by the statement, "The noise contribution of a differential pair to VCO phase noise does not change with W/L if the Gm of this pair ...". It makes it easier to respond to your question. Best Regards, Sheldon |
Title: Re: noise folding in VCO Post by chenyan on Dec 17th, 2006, 7:20am Sheldon, You can find this statement in "The designer's guide to high-purity oscillators" by Hegazi on page 57. Although the deduction is somehow wrong and unclear, but this statement however fits my calculation too. Best regards Chen |
Title: Re: noise folding in VCO Post by neoflash on Jan 1st, 2007, 1:10am I guess Emad's book contains something to reply your question. 1. larger W/L increase harmonics, the more harmonics, the more phase noise we have. 2. larger W/L increase Ctail, thus more upconversion of low frequency tail noise. MIT published a new paper on it 2005 JSSCC Feb. You can go and have a look. rfmems wrote on Dec 17th, 2006, 7:20am:
|
The Designer's Guide Community Forum » Powered by YaBB 2.2.2! YaBB © 2000-2008. All Rights Reserved. |