Good day.
I am running the following simple simulation (spectre 17.1.0):
rx (xx yy) resistor r=50
port11 (xx vssa) port r=50 isnoisy=no
port12 (yy vssa) port r=50 isnoisy=no
sp sp ports=[port11 port12] start=100M stop=1G dec=80 \
donoise=yes file="res.s2p" datafmt=spectre paramtype=s noisedata=cy annotate=status
This is a 50Ohm resistor, connected between two 50 Ohm noiseless ports. When I look at the resulting file "res.s2p" I see the S-parameter noise correlation matrix:
0.023 -0.023
-0.023 0.023
I would like very much to understand how this matrix defined in SPECTRE, since I fail to arrive at these numbers no matter how I try to define the matrix.
The S matrix itself is, by the way, perfectly sound:
1/3 2/3
2/3 1/3
I also tried to use "paramtype=y" (i.e. Y params instead of S params), the noise correlation matrix becomes:
0.02 -0.02
-0.02 0.02
which makes perfect sense (Y-param noise correlation, i.e. 1/R, if I divide by 4kT df).
I apologize ahead if this is some stupid numerical error on my behalf; have spent quite some time on this, and could find nothing in docs. I filed cadence support request, but perhaps knowledgeable folk will answer faster
Help is much needed.
Thanks!