LTspice small signal BJT parameters

[w lubbers]

Hi you all,

does anyone know how to get the small signal parameters of a
transistor out of LTspice, I am used to get these in the .out file
from the good old spice simulators but I can not find anything similar
in LTspice.
I'm especially interested in transconductance, Rpi, Ft, Gm, Cpi,
BetaDC/AC and Rout.

Thanx !!

Waldemar

 

[Mike Engelhardt]

Waldemar,

does anyone know how to get the small signal parameters of a
transistor out of LTspice, I am used to get these in the .out file
from the good old spice simulators but I can not find anything similar
in LTspice.
I'm especially interested in transconductance, Rpi, Ft, Gm, Cpi,
BetaDC/AC and Rout.

Do a .op analysis and then execute menu command View=>SPICE Error Log.

--Mike

 

[Kevin Aylward]

Waldemar,


Do a .op analysis and then execute menu command View=>SPICE Error Log.

Interesting one. Have you inverted 1/hoe so that it outputs ro instead.
I did, as no one but none things in terms of hoe.

How come LTSpice don't seem to accept things like

..SAVE @QN8[ri] @QP12[gm] @MN2[vdsat] @QP12[vbe]

which produces these results as proper sweeps in transient and DC
analysis.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Mike Engelhardt]

Kevin,

How come LTSpice don't seem to accept things like

.SAVE @QN8[ri] @QP12[gm] @MN2[vdsat] @QP12[vbe]

which produces these results as proper sweeps in transient
and DC analysis.

LTspice never used the SPICE3 output routines. It uses
it's own routines in the interest of adding dynamic file
compression of the .tran data.

BTW, while it's not too hard to put out some numbers for
these data for a .tran analysis, it's somewhat non-trivial
to do correctly since the device evaluation functions have
to be called with special flags to initialize the underlying
data used by the routines that extract these parameters.
These flags can conflict with the one ones needed for the
predictor step so you end up with a fair bit of device
evaluation overhead and/or dubious data reported for these
types of parameters. In LTspice, we made a strategic
decision to remove a rarely used function that didn't give
reliable data the make LTspice faster and more correct.

--Mike