# Thermal Noise Source

## Multisim Help

Edition Date: February 2017
Part Number: 375482B-01
View Product Info Multisim 14.0 and 14.0.1 Help Multisim 14.1 Help Multisim 14.2 Help

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.

Thermal Noise results from charges bound to thermally vibrating molecules, which produce EMF (electro-motive force) at the open terminals of a conductor.

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.

The rms voltage associated with Johnson Noise in a resistor R, at the temperature T (Kelvin) over a bandwidth B (in Hertz) is given by the equation:

Vrms (B) = NOISE_FACTOR*(4kTRB)^1/2 volts, where k = Boltzmann’s Constant = 1.38 e-23 j/d)

The mean power over a bandwidth B is given by the equation:

Power (B) = 4kTRB watts

To set up the Thermal Noise Source, input the required parameters in the Value tab of the component’s properties dialog box. (Double-click on the placed component to access the dialog box).

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