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Nexxim Simulator >
Nexxim Component Models >
S-Parameter Elements >
   Noise in S-Parameter Elements       

Noise in S-Parameter Elements

By default, DC and frequency-domain analyses of S-parameter models look in the Touchstone file for noise data. If the file does not supply external noise data, an internal noise model generates the noise data. The S-Element option and instance parameter NOISEMODEL selects the noise data source:

• Use external data if present, or the internal noise model when no external data is present.

• Use only the internal noise model.

• Turn off all noise calculation.

 

Internal Noise Model

In Nexxim, a noisy electronic circuit is modeled as a noiseless circuit plus external noise sources for which certain noise characteristics are known. The noise sources are represented as current sources, which are defined in terms of a so-called Sxx matrix. The Sxx matrix for a two-port device states the noise behavior at a frequency point as:

where iniinj is a noise correlation factor between currents i and j.

The TouchStone format allows for noise specification of circuit devices of up to two ports. The noise characteristics are :

• Minimum noise figure (Fmin) in dB.

• Source reflection coefficient to realize Fmin (Gopt), specified in the Touchstone file as two values, magnitude and phase.

• Normalized effective noise resistance (rn).

All of these parameters are specified against frequency. The parameter Gopt is a complex VALUE, . The noise characteristics are specified as a noise block appended after the S-parameter block in a TouchStone file, formatted according to the TouchStone standard. Nexxim performs a transformation from the noise parameters found in the TouchStone file to the noise matrix Sxx, as explained in Gonzales [1984] (See General References [1] in the S-Parameter References).

In Nexxim’s internal noise model, circuit noise is inferred from the S-parameters.

Noise Example

Here is a shortened example of a two-port Touchstone file with noise data:

!2-port S-parameter file with noise data

# GHZ S RI R 50.0

!freq ReS11 ImS11 ReS21 ImS21 ReS12 ImS12 ReS22 ImS22

1.000 0.393 -0.121 -0.001 -0.002 -0.001 -0.002 0.393 -0.121

!Noise Parameters

4 0.7 0.64 69 0.38

8 2.7 0.46 -33 0.40



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