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Design >> RF Design >> with Divider2,phase noise does not improve 6dbc/Hz
https://designers-guide.org/forum/YaBB.pl?num=1133146107

Message started by Juddy on Nov 27^th, 2005, 6:48pm

Title: with Divider2,phase noise does not improve 6dbc/Hz
Post by Juddy on Nov 27^th, 2005, 6:48pm

Hi all,
I use vco+div2 as my LO generator. here is the simulation results,
without div2(4GHz), -105@100k, -135@3M
with div2(2GHz), -110@100k, -140@3M (just 5dbc/Hz improved)
From the noise contribution, it can be seen that the devices of div2 contribute a lot(20%), especially the bias of div2.
Also, my vco output peak-to-peak swing is around 1v(single end) without any load, but turn to 700mv with div2 as loading.
I simulated the phase noise of the div2, and its PN from 100k to 10M is about -150dBc/Hz. so I think div2 itself should not contribute
so much noise.
Does anybody know what's wrong with this.

Thanks in advance.

Title: Re: with Divider2,phase noise does not improve 6db
Post by vborich on Dec 2^nd, 2005, 8:23pm

The 6 dB improvement you expect assumes an ideal divider that doesn't load the oscillator. If it does, as you measured, then it affects the oscillator's steady state operation and consequently its phase noise.