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

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