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Thermal Noise spectrum of a resistor

kenambo

HI..


  Is it possible to view the thermal noise which is constant over the bandwidth can be seen or plotted visually in cadence virtuoso and can we measure the MOSFET's thermal noise by this manner .. If so it can also be seen visually?

Thanks.

Parents

  • Yes. If you run a noise analysis, you can go to Tools->Results Browser and navigate into the "noise" results. You'll see each device, and within that each noise source - so fn, rd,rs etc (depends on the model). The "r" are the thermal noise due to the resistances in the models. You can then plot these in the graph, or send them to the calculator (e.g. if you want to take the sqrt so that you get them in Units/sqrt(Hz) rather than Units^2/Hz.

    The numbers you see are output referred - so this means that it is showing you the amount of noise that this noise source contributes at the output of the circuit. That may mean that the plot is not flat if there is any band-limiting of the signal from that point in the circuit to the output.

    There is a feature in pnoise analysis called "noise separation" which allows you to plot the noise at the noise source itself - but that's only available in pnoise/hbnoise and not in standard noise. It's more useful in the RF domain because it also allows you to figure out which sidebands the noise is coming from too (although I can see it would be useful in standard noise analysis; it's just not been implemented).

    Regards,

    Andrew.

Reply

  • Yes. If you run a noise analysis, you can go to Tools->Results Browser and navigate into the "noise" results. You'll see each device, and within that each noise source - so fn, rd,rs etc (depends on the model). The "r" are the thermal noise due to the resistances in the models. You can then plot these in the graph, or send them to the calculator (e.g. if you want to take the sqrt so that you get them in Units/sqrt(Hz) rather than Units^2/Hz.

    The numbers you see are output referred - so this means that it is showing you the amount of noise that this noise source contributes at the output of the circuit. That may mean that the plot is not flat if there is any band-limiting of the signal from that point in the circuit to the output.

    There is a feature in pnoise analysis called "noise separation" which allows you to plot the noise at the noise source itself - but that's only available in pnoise/hbnoise and not in standard noise. It's more useful in the RF domain because it also allows you to figure out which sidebands the noise is coming from too (although I can see it would be useful in standard noise analysis; it's just not been implemented).

    Regards,

    Andrew.

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