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Phase Noise vs frequency graph problem

rohan kr

Hello

I am a newbie engineer starting my career in IC design and working on a  high frequency oscillator (38 GHz). I am using Cadence IC6.1.5-64b.500 version and using spectre simulator for the schemtic design and simulations.

 I am having doubts about my 'pnoise' analysis. All the research papers I have referred show the graph of phase noise (dbc) vs. frequency which have values of phase noise(PN) in negative i.e. around -90 to -100 dbc (the graph should be like the flicker noise graph) but I am getting positive  values of PN(with similar type of curve). I have used the 'relative harmonic as 1 and all the settings seem to be as described in the cadence simulation guide. 

 I have referred most of the  community forum in EDAforum,designer-guide and even the Cadence community...there are problems related to this..but there is no definite answer as to how i can get the correct graph as shown in most of the research papers...In one of the community one guy gave an explanation of the equation spectre uses to simulate pn...My question is whether i need to make changes in the circuit or some settings in cadence...

Kindly help me as it is my first major project and need to do well...thanks in advance.. 

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  • Frank Wiedmann

    It's very difficult to tell what the reason for your problem is without being able to examine your circuit in detail. I don't see any obvious errors, but you should try if selecting conservative accuracy defaults changes anything and should make sure that you are using the oscillator mode of the pss analysis and a recent version of Spectre.

    If that doesn't help, ask an experienced colleague to examine your circuit or submit it to the Cadence Support. The problem could be anywhere: from unrealistic noise parameters in your transistor models to problems with the sizing of your circuit components, leading to incorrect operating points.

Reply
  • Frank Wiedmann

    It's very difficult to tell what the reason for your problem is without being able to examine your circuit in detail. I don't see any obvious errors, but you should try if selecting conservative accuracy defaults changes anything and should make sure that you are using the oscillator mode of the pss analysis and a recent version of Spectre.

    If that doesn't help, ask an experienced colleague to examine your circuit or submit it to the Cadence Support. The problem could be anywhere: from unrealistic noise parameters in your transistor models to problems with the sizing of your circuit components, leading to incorrect operating points.

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