# Linear noise calculation

Question asked by JERRY_MARKETOS on Apr 7, 2005
I recently encountered a question regarding how noise analysis is performed in cases
where there's no noise data in a datafile.  I thought others might also benefit from the
answer, so I'll post here.  Attached PDF file is the referenced  MTT article.

When specific noise data is not present, a test is made to determine whether the device
is reciprocal or nonreciprocal.  (Essentially, reciprocal tests whether the device's Y matrix is
symmetrical with respect to Y21 and Y12).  Items such as inductors and symmetrical networks
of passive components are reciprocal.  An example of a nonreciprocal network would be that of
an amplifier (where Y21 doesn't equal Y12) or also possibly a network of nonsymmetrical passive components.
(Think of a typical Tee attenuator with inductor to ground at only one of its ports...  The network is still passive,
but the impedance seen from each port to ground is very different at DC and low frequency)

If the network is found to be reciprocal,
the noise correlation matrix is calculated from its Y-matrix according to:    (see reference note  )

C = 2kT*(Y + Y*) = 4kT * Re(Y)
The formula is used for reciprocal elements, (when Y[i,j]=Y[j,i])

If the network is found to be nonreciprocal, then the same formula is used,
but the calculation is only performed on the diagonal elements of the Y-matrix.
All non diagonal elements of the Y-matrix are set equal to zero.

  MTT-33, No. 12, December 1985, page 1507,Computer-Aided Noise Analysis of
Linear Multiport Networks of Arbitrary Topology, Rizzoli & Lipparini.

[file]rizzoli_linernoise00029010.pdf[/file]