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Ring oscillator or LC tank?

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mazelk

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Hi, i'm looking for a good desing for VCO at 0.35 CMOS technology, and i have meet with ring oscillators and differential LC tanks are more usual implementation. According phase-noise, which be better?.

Also i'm looking for implementations that meet a levels of phase noise lower than -110 dBc/Hz, offset 25 kHz at GSM frequency (or approx, I don't sure).

I thank in advance your constructive answers.
 

My experience has been that ring oscillators draw more current and have worse phase noise than LC. Ring oscillator Q=1 so phase will always be better with LC.
 

the LC oscillator is better in phase noise than ring oscillator
but ring oscillator have a wide tunning range

i have design a fully integraeted VCO in my garduation project using 0.35 cmos technolgy , and the Q of the varactors was about 30 to 40 and the quatity factor of the oscillator was 4.4 to 5

and which is better it depends on the application u will use the oscillator in
low phase noise (LC) wide tuunng range (ring )

also if u used the ring oscillator it will be very easy to generate I Q signals of the oscillator
but in LC u will need two quarature oscillator (big area ) for coils
 

hi mazelk,

i am studying the LC VCO now. Many IEEE papers show that the LC VCOs have better noise phase noise than ring VCO, and the ring VCOs have better tuning range than LC VCO.

So I think which VCO depends on your spec. I ever see many papers use ring VCO applied into GSM frequency and LC VCO into 2.4G frequency.

I hope my view will give you a hand.
 

Regarding the phase noise, definitely LC type is better than ring oscillator. Usually 20db better.
 

I did not see the option CLASSES -> FREQUENCY SYNTHESIZERS
May this page have had changes ?
 

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