Why is Thermal Noise Bandwidth Not Limited in Multisim?

Updated Mar 29, 2019

Reported In


  • Multisim 11.0.1 Full

Issue Details

I need to simulate the thermal noise made by a resistance with a THERMAL_NOISE component. I've configured the parameters in the Value tab, including the Bandwidth


If I add a probe, I no longer see the value I selected before. Why?


The Thermal Noise Source uses a Gaussian White Noise model to simulate thermal noise (also known as Johnson noise) in a conductor. It can be placed in series with a resistor to emulate the thermal noise generated by that resistor.

One disadvantage of using a Gaussian White Noise model for this purpose is that its power would be infinite. However, the model is valid over a limited bandwidth (B) as all EMF fluctuations outside of the defined bandwidth are ignored. That's why you see an unrestricted band signal. In reality, the values are valid in the band you define, but invalid out of it. That's why you see a 2.5MHz signal.