Trust PSS or Transient simulation for VCO?

[haadi20]

I encounter a difference in the simulated value of VCO output frequency when i run transient and PSS simulation...is this normal? has anybody experienced the same issue?

As an e.g. I get a frequency of 37 GHz from transient simulation (by using the frequency function from the calculator on the differential output voltage)

Whereas, the PSS finds an oscillation frequency of 38 GHz. I use Moderate as errpreset.

My question is which simulation result should i trust in designing for a specific tuning range?

Regards

 

[khouly]

check this link it is a appnote how to use spectreRF in oscillator design

ususally ppl use PSS periodic steady state , not the transient analysis
also the noise PSS to get the phase noise of the oscillator

www.cdnusers.org/community/virtuoso/resources/SpectreRF_VCO533AN.pdf


khouly

 

[BigBoss]

PSS is more accurate than transient by using frequency function because of "settling of the frequency" at the beginning of transient state of the circuit. In generally, oscillator simulations are done by PSS NOT transient and also 37GHz is too much for MODEL continuity of the both passive and active components.

So 1GHz difference my be normal..

 

[haadi20]

...and also 37GHz is too much for MODEL continuity of the both passive and active components.

So 1GHz difference my be normal..

My apologies...i could not understand the above statement...can you please elaborate ?

Regards

 

[BigBoss]

...and also 37GHz is too much for MODEL continuity of the both passive and active components.

So 1GHz difference my be normal..

My apologies...i could not understand the above statement...can you please elaborate ?

Regards

I meant, at 37GHz models for both active and passive components are not very accurate anymore due to skin effect, dispersion effect, scattering etc. Therefore the models which are used by PSS might not be very accurate. Because PSS searches steady state regime and during this period, models can be very variable so that transient simulator can do some errros..