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Phase noise using noisetype=sources vs noisetype=pmjitter (Read 195 times)
deba
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Phase noise using noisetype=sources vs noisetype=pmjitter
Jul 19th, 2017, 6:20am
 
Hi,

I have few question regarding pnoise available in spectreRF.

1) For a square wave, the phase information is only present at the rising or falling edges. Thus, the phase noise(in dBc/Hz) obtained from noisetype=sources will be equal to the one obtained from the one using noisetype=pmjitter(the voltage noise is converted to phase noise).

Is the above reasoning applicable to sinusoid oscillators(VCO,crystal)? I think pmjitter cannot be applied to these cases. So if there are sinusoid then only noisetype=sources is applicable.

2) For a driven circuit, if one limits the amplitude using a VCVS(limiter with gain=1 around the threshold crossing) and use noisetype=sources. The phasenoise obtained using this method will be the same as the one obtained using pmjitter. So the utility of pmjitter is not clear. Can someone clarify?

Thanks

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Jacki
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Re: Phase noise using noisetype=sources vs noisetype=pmjitter
Reply #1 - Sep 22nd, 2017, 5:35am
 
Hi,

   According to my understand between pmjitter and source, the former one has the strobed jitter, and source gives the time-averaged jitter. for driven circuits, i think pmjitter is a good choice since you have your reference input clock.
   I think we can also separate them like: fast variation or slow variation, it depends on the output of your circuit.
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Ken Kundert
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Re: Phase noise using noisetype=sources vs noisetype=pmjitter
Reply #2 - Sep 22nd, 2017, 9:13am
 
I have not used pmjitter myself, so I cannot speak to the details, but conceptually a jitter analysis will:
  • As Jacki says, a jitter analysis will sample the noise at the threshold crossing and report only the jitter at the threshold crossing. No sampling is performed in a conventional noise analysis.
  • A jitter analysis reports its results in seconds rather than volts or amps.
  • A jitter analysis computes the jitter directly and without requiring you to add a limiter to your circuit.

-Ken
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