QVCO designing

Nobody is going to be able to help you if they don't know which technology  you are using or what your circuit looks like. Even then there are probably better forums (e.g. Designer's Guide) to answer detailed design-related questions (but you'll need to make sure you follow the forum guidelines there too and provide enough info for somebody to stand some chance of answering your question).

Hi,

Thank you very much for your reply i'll try to correct my previous mistake please tell if i make some this time regarding posting my query.

I am sending you screen shots of my design please have a look. i also attached a transient response in the end where you can see the negative part of the wave is not proper due to which oscillation are not getting sustained. I am also thinking that may be Inductor and Capacitor are not functioning well in the RF region of operation, Vdc & Vcc are also varied from -1.8V to +1.8V and the aspect ratio is also varied from 1 to 700 of all the mosfets whether they are coupling, biasing or providing -ve resistance. All this is done at 180nm technology node and using cadence virtuoso version icfb.exe version 5.1.0 sub version 5. 10. 41_USR5. 90. 69.  Please comment, if you need some other details to figure out the problem please do tell me.

 Dear Vivek1729,

> i also attached a transient response in the end where you can see the negative part of the wave is

> not proper due to which oscillation are not getting sustained. I am also thinking that may be Inductor

> and Capacitor are not functioning well in the RF region of operation,

 I believe your oscillator is functioning as expected. There is no guarantee in your circuit that the oscillation waveform will have low distortion (which I believe is what you are looking for). The amplitude of the oscillation - and the waveform itself - will be determined by the magnitude and phase of the waveform that provides a steady-state impedance that exactly balances the steady-state impedance of your resonator (inductor in this case). There is some filtering by the LC tank, but that is not narrow band enough to eliminate distortion products. If you are looking for a very low distortion waveform, there are other techniques that are used to limit the amplitude of the waveforms or to use a very narrrow band resonator. Limiting the amplitude basically causes the negative resistance of the sustaining amplifier to drop in value as the amplitude grows and hence reduces distortion.

 However, if I have understood your question (I hope I have!), the behavior does not reflect any simulator issue nor an issue with your capacitor or inductor.

Shawn