Subject: Re: Determining bjt noise parameters for Spice models?
Date: Fri, 13 Dec 2002 20:46:55 +0100
Organization: Wanadoo, l'internet avec France Telecom
References: <3DF6537E.B0FC9DBE@worldonline.fr> <3DF90203.C9691374@worldonline.fr> <3DF98E5B.D86102A5@worldonline.fr>
NNTP-Posting-Date: 13 Dec 2002 19:46:55 GMT
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Kevin Aylward wrote:
> >>> - common emitter;
> >>> - collector connected to a voltage source in series with a
> >>> resistance;
> >>> - base directly connected to a voltage source (VSRC, small AC);
> >>> - the base voltage source adjusted to get about 10mA collector
> >>> current;
> >>> - equivalent input noise calculated as V(ONOISE) on the collector
> >>> divided by the gain calculated (by Spice)
> >>> on the input AC.
> >>> Doing that with the standard 2SC3329 model and varying RB from 2 to
> >>> 10 Ohm could not reach the 0.6nV/rtHz specified by the datasheet -
> >>> much lower levels obtained; the datasheet announces rb about 2Ohm.
> >> I dont understand whatvyou say here. Is the spice value too high or
> >> too low?
> > Sorry. The value calculated (not directly by Spice but by me, from
> > the V(ONOISE) provided by Spice) was much lower than 0.6 nV/rtHz.
> At 290 deg, 20 ohms gives 0.57 nv/rthz. At 10ma the collector noise =
> 0.141 nv, which is getting close to 0.6nv when you sum the squares.
> What does the spice V(INOISE) give?
A) the initial, stock model: has RC=5.9, RB and RE missing (so =0); with
collector current of about 10mA, collector voltage about 9V, collector load
of 1kOhm, V(INOISE) is about 0.14 nV/rtHz.
In the noise analysis printout, Spice gives "RC=1,800e-22
B) RB=10 added to the model, in the same conditions, V(INOISE) is about
BTW, the datasheet is located here:
It says, in particular, "low base spreading resistance: rbb ' = 2.0 Ohm
> Kevin Aylward
> SuperSpice, a very affordable Mixed-Mode
> Windows Simulator with Schematic Capture,
> Waveform Display, FFT's and Filter Design.