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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.. 

Parents

  • Hello Tawna,

     I am very thankful for your reply...Read a lot of posts by you and Andrew in various topics and a fan of your knowledge and work..

    I got the correct graph yesterday when I changed errpreset to 'moderate' and putting tstab as 60n..but the values of phase noise was aroung -140dbc/hz at 1Mhz offset...I was surprised as to how it could be so low...

    Today,after reading your post,I changed errpreset to 'conservative' & the simulation is failing..the output logs  had few warnings-

    C0.dsx.dnwx:breakdown voltage exceeded 

    C0.dsx.dnwx:junction current density exceeds 'imax'

    and after that the error came-

     maximum number of iterations reached.Simulations failed to converge.you can try to increase tstab and harms.

     I increased the tstab from 60n to 100n and the harmonics from 10 to 20...the simulation still fails...

    Also, thanks for the urls you posted...it helps just knowing that people are there to help amateurs like me...

     

Reply

  • Hello Tawna,

     I am very thankful for your reply...Read a lot of posts by you and Andrew in various topics and a fan of your knowledge and work..

    I got the correct graph yesterday when I changed errpreset to 'moderate' and putting tstab as 60n..but the values of phase noise was aroung -140dbc/hz at 1Mhz offset...I was surprised as to how it could be so low...

    Today,after reading your post,I changed errpreset to 'conservative' & the simulation is failing..the output logs  had few warnings-

    C0.dsx.dnwx:breakdown voltage exceeded 

    C0.dsx.dnwx:junction current density exceeds 'imax'

    and after that the error came-

     maximum number of iterations reached.Simulations failed to converge.you can try to increase tstab and harms.

     I increased the tstab from 60n to 100n and the harmonics from 10 to 20...the simulation still fails...

    Also, thanks for the urls you posted...it helps just knowing that people are there to help amateurs like me...

     

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