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CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio (Read 3443 times)

deba

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CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio
Nov 09^th, 2016, 4:44am

Hi All,

For ring oscillators, it is known that by tuning the pMOS/nMOS ratio one can get a symmetric waveform. Resulting in minimizing the phase noise and 1/f^3.

1) Does the same phenomenon happen for CMOS LC VCOs?
2) And if it happens, is it applicable in both current and voltage limited regions of operation of VCO?

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Horror Vacui Senior Member Offline Posts: 127 Dresden, Germany	Re: CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio Reply #1 - Nov 30^th, 2016, 11:02am 1) How does the waveform of an LC VCO looks like? This will answer your question. 2) What do you mean by current and voltage limiting? There is amplitude limiting usually due to a finite supply. I do not think in current and voltage limited regions.
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deba Community Member Offline Posts: 84	Re: CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio Reply #2 - Dec 7^th, 2016, 5:02pm Hi Can you elaborate on the point "how does the waveform looks like"? In current limited regime, the swings are proportional to the tail current. In voltage or supply limited regime, the max voltage swing is supply Vdd.
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sarge

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Re: CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio
Reply #3 - Dec 14^th, 2016, 4:15pm

deba wrote on Dec 7^th, 2016, 5:02pm:

Hi

Can you elaborate on the point "how does the waveform looks like"?

In current limited regime, the swings are proportional to the tail current. In voltage or supply limited regime, the max voltage swing is supply Vdd.

Hi,

I think the point here is that LC VCO has sinewave waveforms, and ring has CMOS.
Sorry for interrupting your conversation

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Horror Vacui Senior Member Offline Posts: 127 Dresden, Germany	Re: CMOS LC VCO phase noise sensitivity to pMOS/nMOS ratio Reply #4 - Jan 9^th, 2017, 2:13am Exactly. A meaninful LC VCO has a high enough Q to suppress the higher order harmonics. So it is a fruitful approach to consider its waveform sinusoidal.
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