Are SpectreRF VCO phase noise results trustworthy?

[rainsender]

vco phase noise

I designed a 2.4GHz LC VCO using cadence. But the Spectre simulation gave me very large phase noise as shown in the figure. I know it's common to see positive phase noise using Spectre at low offset frequency. But what I got is more than 100 dBc. I tried to tighten the simulation Tolerance Options, 1e-5 for reltol, 5e-8 for vabstol, 1e-13 for iabstol, and selected gear2only as integration method, but there was little differnce. I also ran transient analysis and plotted the DFT to confirm the center frequency, and it turned out right. The current is around 6mA, which I think is large enough. I am a little crazy on this now. Anyone can explain this to me?

 

[playoff]

poddar+vco

I still doubt there is some simulation setting problems
Maybe you should check the PN contribution first

 

[bless_fooling]

phase noise vco spectre

You can use matlab to validation your simulation result with cadance

 

[AdvaRes]

phase noise spectrerf

Hi,

I have the problem. My VCO simulation gives exatly the same result as yours. Thats weird. Look at the figure.
Also I have a filter that has a -35 dbc at 1Mhz and I dont know why.
Could sombody help ?

I still doubt there is some simulation setting problems
Maybe you should check the PN contribution first

Could you please explain how to use matlab for phase noise simulation ?

Thanks in advance.

 

[N1UL]

vco spectrerf

Hi guys,

your results MUST be wrong since a 6 KHz Hz off the carrier the phase noise cant be more then the output power of typically 0 to 10 dBm. Also the curve cant be correct as there is no flicker frequency contribution . I don't have ever used cadence RF ,I would recommend to use either Ansoft Serenade version 3.5. version 4 is broken or ADS with the proper library. The key is that the transistor parameters are correct and the bias also. The phase noise of a passive device (filter) must be equal to its losses

General comments on noise :

The early oscillator pioneers like Leeson, Driscoll, Healey III , Parker and others did their analysis based on linear assumptions, which do not get the same good results as available today. The modern methods require large signal parameters which Agilent now calls X parameters. Provided that the input parameters for the models are OK, the harmonic balance simulators can tackle this. I prefer measurements , using a network analyzer and then a set of analytic equations. The results for modern planar resonator based oscillators up to 20 GHz are much better then the conventional predictions without dealing with the conduction angle of the current and suppressing or even enhancing certain harmonics

This modern approach, heavily depending on non liner analysis and mathematics shows a further improvement, by reducing the AM to PM conversion, both modulation and conversion noise (close in and far out noises are different in their origin).

It applies both for crystal oscillators and printed resonators and other solutions. I will follow up with a series of IEEE publication and validations , but the curious readers may find the basic presentations useful.
The Design of Modern Microwave Oscillators for Wireless Applications, by Ulrich L. Rohde, Ajay K. Poddar, Georg Böck, published by John Wiley & Sons, New York, NY, May, 2005, ISBN 0-471-72342-8.