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zhaofeng1983
Joined: 23 May 2007
Posts: 54
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 21 Jul 2008 10:54 wierd VCO pnoise vs current |
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Dear All,
I am designning a PMOS cross-coupled VCO with PMOS current tail. When I sweep the current bias from 3mA to 4mA the output pnoise varies a lot. The VCO frequency is 2GHz. The pnoise at 1MHz offset with current of 3.8mA is -125dBc/Hz while the noise increases to -115dBc/Hz with a current of 3.9mA or 3.7mA. I don't know whether the model is accurate. Do you guys have any ideas? If I have to design the VCO with this technology, which simulation results should I choose? I am so confused and depressed.
Thank you.
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jecyhale
Joined: 19 Feb 2008
Posts: 402
Helped: 39
Location: China
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| 22 Jul 2008 5:53 Re: wierd VCO pnoise vs current |
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| zhaofeng1983 wrote: |
Dear All,
I am designning a PMOS cross-coupled VCO with PMOS current tail. When I sweep the current bias from 3mA to 4mA the output pnoise varies a lot. The VCO frequency is 2GHz. The pnoise at 1MHz offset with current of 3.8mA is -125dBc/Hz while the noise increases to -115dBc/Hz with a current of 3.9mA or 3.7mA. I don't know whether the model is accurate. Do you guys have any ideas? If I have to design the VCO with this technology, which simulation results should I choose? I am so confused and depressed.
Thank you. |
Yes, I have met this question too.
I think we should not trust the simulation result so much.
And you can only trust the the average of the result.
So the one time reslut is not the fact.
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khouly
Joined: 20 Oct 2003
Posts: 2421
Helped: 331
Location: EGYPT
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| 22 Jul 2008 6:39 wierd VCO pnoise vs current |
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maybe the models it not so accurate.
khouly
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zhaofeng1983
Joined: 23 May 2007
Posts: 54
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| 22 Jul 2008 10:38 wierd VCO pnoise vs current |
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| Thakns. It is possible that the model is not so accurate. The PDK provides only RF model for the channel length of 0.35um, so I can't change the length to reduce the phase noise. Is there any other good ways to push the 1/f^3 noise to less than 500Hz? Is there good refs on the reduction of flicker noise in VCO or reducing the 1/f^3 noise corner?
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khouly
Joined: 20 Oct 2003
Posts: 2421
Helped: 331
Location: EGYPT
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| 22 Jul 2008 10:41 wierd VCO pnoise vs current |
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i think we need opinion of one of the VCO experts here
but if the technology is 0.35 , u can't go less than this length
khouly
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