Programming instructions

Thermal Noise Source
 National Instruments Corporation 1-47 Multisim Component Reference Guide
1.42 Thermal Noise Source
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) = (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).
1.43 TDM Source
The TDM source is used to input National Instruments binary measurement files (.tdm) into
a Multisim simulation. It is available as both a voltage source and a current source.
 To set up the TDM source:
1. Double-click on the TDM source to open its properties dialog box and click the Va l u e tab.
2. In the File area:
•
Filename — click on the button to the right of this field and navigate to the desired
.tdm file. When the Select Trace dialog box appears, enter the desired Group,
Channel X and Channel Y data, or click OK to accept the default settings.
TDM Voltage Source TDM Current Source
ComponentRef.book Page 47 Thursday, December 7, 2006 10:12 AM