Subject: Determining bjt noise parameters for Spice models?
Date: Tue, 10 Dec 2002 21:50:06 +0100
Organization: Wanadoo, l'internet avec France Telecom
NNTP-Posting-Date: 10 Dec 2002 20:50:08 GMT
X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.20 i686)
I wanted to predict noise properties of some bjt-based circuits using
Spice. Then I've noticed that the bjt models (almost) never include the
noise parameters (AF, KF ). How can those be determined from the data
I've tried the advice found in a Spice manual: set AF=1 and then find
KF such that it gives the requested noise figure; I've tried this for
2SC3329. Ok, I've found something like KF=5e-15 to get the specified
NF at 1 kHz with Ri=20k. Then I've varied the collector current but have
not observed the specified NF changes! I've then looked at the NF at
10Hz. Apparently, AF=1 does not fit this transistor; I've tweaked it
to AF=1.13 to get the noise figures ressembling those in the datasheet,
but without knowing what I am doing!
- would it be possible that someone explains the meaning of AF and KF
(refer to an on-line doc, etc.) and how to calculate them from the
- in general, is the bjt model in Spice capable of precisely enough
modelling the noise behaviour of all the bjts out there (in particular:
2SC/2SA Toshiba/Hitachi low-noise series)?