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Phase noise simulation of an XOR gate based frequency doubler

lahsivece

Hi ,

I am trying to calculate phase noise at the output of an XOR gate. The XOR gate input are two quadrature clocks @ 500MHz and output is a 1GHz clock. I have some arbitrary noise spectral density ( phase noise ) assigned to the 500MHz clocks upto 500MHHz frequency offset from the carrier(500MHz in this case). I want to see the phase noise curve for the output of the XOR gate at 1GHz.

Please let me know if the following methodology is correct :

1) Shooting pss with beat frequency 500MHz, 10 harmonics , errpreset=moderate , tstab=100ns (circuit stabilizes pretty quickly)

2) pnoise setup : beat frequency = 500MHz (evaluated from the pss analysis); sweeptype = relative ; relative harmonic=2  ( 1GHz is second harmonic of 500MHz and is the output frequency of XOR gate); Input source= Voltage ( Arbitrary phase noise profile has been assigned to the source). Reference sideband = - 1 ( as 500MHz=1GHz-1*500MHz.).

Is the pnoise setup described above is correct ?

Is the same pnoise setup valid for any subharmonic injection locked system ?

Thanks & Regards

Vishal


 

  • Vishal,

    1. You may not need as long as 100ns tstab. It's not required to be fully settled - the algorithm can find that for you.
    2. The input source and refsideband are only needed if you want to compute input referred noise or noise figure. For output noise or phase noise they aren't needed. Not sure how you've defined the phase noise profile on the input source - you should be careful about that because typically by just specifying a noise frequency curve you aren't taking into account the fact at multiples of the carrier are correlated - but you can set the noise type on vsource/port to be "SSB Phase Noise (dBc)" provided you're using an IC616 version and MMSIM13.1 (I think those are the minimum versions).

    Apart from that, the setup looks OK.

    Hard to tell whether this is also correct for "any" subharmonic injection locked system... the key is that the PSS is the lowest common frequency, and that the pnoise is sweeping around the right relative harmonic that you care about for measuring the noise at.

    Regards,

    Andrew.

  • Hi Andrew ,

    Thanks for the suggestions and clarifications.

    1) tstab of 100ns is just a number that I am using for settling . In general the algorithm finds it for me.

    2) Regarding input noise source : I will specify it as none.

    3) Currently I am using a measured phase noise profile of a signal generator  as the phase noise profile of source and using method described in

    http://community.cadence.com/cadence_blogs_8/b/rf/archive/2012/05/24/modeling-oscillators-with-arbitrary-phase-noise-profiles

    With Best Regards,

    Vishal

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