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shiva Guest	VCO jitter Nov 07^th, 2005, 7:00am Hello, I know it's a pretty open question, but I'm a bit stuck, so here it goes: anyone has a good idea/reference on how to model the phase noise/jitter of a VCO using VHDL-AMS? Kind Regards Peter
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Ken Kundert Global Moderator Offline Posts: 2386 Silicon Valley	Re: VCO jitter Reply #1 - Nov 7^th, 2005, 11:40am Check out http://www.designers-guide.org/Analysis/PLLnoise+jitter.pdf. It describes how to build such a model for Verilog-AMS. It should be a simple matter to translate the model to VHDL-AMS. -Ken
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Amrsfmt

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Egypt

Re: VCO jitter
Reply #2 - Mar 20^th, 2006, 12:21pm

Hi,
Actually, I tried this in VHDL-AMS, but failed because simply there is no function named phase_noise or noise in VHDL-AMS. I know there is noise sources but not implemented in All tools. For example, the ADMS don't implement the noise sources in VHDL-AMS.

There is 2 solutions for noise:
1- create a noise source in sub-circuit in ELDO spice, and instantiate it in your code and used it in a structural discribtion with your ideal model.

2- create the noise by yourself.

Actually, I made both solutions.

Here is a sin source with noise on it in transient , no noise in AC. Read the code if there is something please post.
Amro

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Vnoisy_gaussian.zip

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Paul

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Re: VCO jitter
Reply #3 - Mar 21^st, 2006, 2:16pm

Hi,

I am using a ring oscillator model in an event-driven fashion (i.e. the output is a square-wave). In that case, you can simply calculate the delay to the next edge and include a random component. The interesting thing is that this uses pure VHDL (or Verilog of course) and doesn't need the AMS extensions.
If you want a sine-wave output, you may use a random signal based on the random number generator and use it to phase modulate your sine wave.

Paul

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Amrsfmt New Member Offline change over Posts: 6 Egypt	Re: VCO jitter Reply #4 - Mar 21^st, 2006, 2:53pm HI, That's exactly what I have made in the code above. Thank you, Amro
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