Positive Phase Noise in Spectre PSS

[mhaghaed]

Hi all,

I've been trying to simulate a simple differential LC oscillator, the one that is explained in Spectre PSS tutorial. However, it gives me positive phase noise at low frequency offsets(~ +50dBc@10Hz), (it gives acceptable negative phase noises for high frequency offsets: -130dBc@1MHz though).
I thought it might be because it couldn't find the exact fundamental freq. So, I gave it the exact fundamental tone I extracted from transient analysis. It didn't work...

Does anyone know if this is a Spectre problem or there is sth wrong with my simulation/circuit?

Hassan

 

[AdvaRes]

Hi,

According to some papers that a I saw LC VCOs have below -100 dBc phase noise at 1Mhz offset for frequency carriers between 1Ghz and 2Ghz.

So, in your case, I think that your simulation in OK.

 

[yendori]

I think his question was about the +50dBc/Hz @ 10Hz. Wasn't it?

 

[knights]

I think this is because the computing method uesed to calculate the phase noise was not accurate in low frequency.You can check the Cadence file about it.

 

[playoff]

According to the oscillator PN curve model, this sim results are not reasonable.
I think you should check the simulation setting.

 

[moghtada]

I have this problem so, I simulated my ring oscillator by cadence and ADS but both results are same. I think it is because of software model and you should ignore it.

 

[pancho_hideboo]

See https://www.edaboard.com/threads/165472/