Thermal Noise spectrum of a resistor

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.

My guess is that your models are subckt models and so have additional components around the transistor, and this is what you are seeing. This however is a guess, because I don't know what PDK you're using - but those names don't normally show up for a bsim4.5 model, as far as I know.

Andrew.

Hi

thanks I think the same too. And along with thermal noise I am seeing a spectrum for flicker noise but it is zero.

How to find flicker noise for a PDK resistor model and how to identify which are the parameters for Noise analysis and Is there a way to turn-off PDK resistor or Mosfet's Noise model? (Both Thermal and Flicker).

Thanks

There are model parameters on bsim4 and resistor and various other components that control the flicker noise - it's not unusual for a resistor to not have flicker noise modeled, but thermal noise you get by default.

You can turn off the noise contributions for individual devices by using Simulator->Options->Analog, and on the Main tab at the bottom, there's a Noise Contribution on/off checkbox. If you select "off", you can then pick the components in your design that you don't want to produce any noise. There was another recent thread which talked about this (in fact more than one) - look for isnoisy, and noiseoff_inst etc.

Regards,

Andrew.

thanks for the reply..

I found that option but do you think we can measure the Thermal noise of a MOS by the same way as the resistor.

Because MOS models also include thermal noise right?

Thanks

kenambo said:

Sorry . I mean Thermal noise of a MOS can be measured? and How to measure the flicker noise for a MOS?

It's still not clear what you're actually asking.