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How to do "multiplication" in freq. domain with provided noise data file?

Cod Liang

Hi all,

Recently I've been doing some noise evaluation issue, the simplified testing environment is as below:

The thing I want to do is to multiply the noise profile defined in both "AVDD" and "TFsquared_AVDD2VCOVDD" sources.

This case is not as simple as that of a VCVS and a noise source since VCVS cannot read the extracted noise data file...

The noise sources are defined as follows:

where "AVDD" noise was given in self-defined noise/freq pairs and "TFsquared_AVDD2VCOVDD" read the .txt noise file.

I tried to do multiplication by the ideal block "multiplier" defined in ahdlLib.

Finally, I ran .noise simulation and plot output noise and instance noise individually.

The first two rows are input noise sources and the final row is the resulting output noise.

It seems that the output noise is not like what I have expected, namely, the multiplication of row1 and row2.

Instead it is the summation of input sources...

I wonder if there is any way to do noise multiplication in Cadence Virtuoso environment?

I would be very grateful for all of your kind help:)

Thanks in advance.

Simulation environment

virtuoso 6.1.7-64b

spectre 16.1.0.440.isr8 32b

  • Andrew Beckett

    This is not surprising, because noise analysis is a small-signal linear analysis. That means that it assumes that for each noise source, it will compute the linearised transfer function to the output - in this case that means that the noise source is being multiplied by the DC value of the other source (this happens whether you use a VerilogA multiplier, or (say) a pvcvsp from analogLib with 2 controlling voltages, and 4 coefficients, with c0-c3=0 and c4=1.0). The noise powers are then summed at the output and the total noise given. Effectively you're seeing superposition of the contribution of each noise source to the output.

    Multiplication of the noise sources themselves would be a large-signal effect, and so is not covered by the small-signal frequency-domain analysis. You'd have to use transient noise to see that.

    Regards,

    Andrew.

  • Cod Liang
    in reply to Andrew Beckett

    Hi Andrew,

    Thanks for your kindly reply.

    Your explanation is very clear and useful.

    Actually, I want to build a linearized phase noise model for a PLL-based synthesizer.

    Which means the whole components in the schematic are analyzed using small-signal analysis method. (.ac, .noise, .pss, etc.)

    In the meanwhile, I hope that the supply-induced spur issue could also be included in my linear model simulation.

    That's why I've been seeking for the solution of this issue. (Given source1 = spur power level I defined and source2 = transfer function from supply to the node of interest)

    So is there any possible way to do this spur-related noise simulation along with linearized noise analysis?

    Thanks a lot.

    Regards,

    Liang

  • Andrew Beckett
    in reply to Cod Liang

    Hi Liang,

    Probably (I've not thought about it enough though) - but if you are expecting the interaction "noise" source representing the spur with the linear noise from other components, that won't happen for the reasons I outlined below. 

    If you've not seen it, I'd also suggest taking a look at this rapid adoption kit: PLL Verification

    Regards,

    Andrew.

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