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Spice Transistor Models at RF

C

cledus

Jan 1, 1970
0
All,

I found the discussions regarding Paul Burridges' FSM design very
enlightening. I have a tangential question, though. Does Spice (LTSpice,
Circuitmaker, etc.) accurately model transistor operation at 40 MHz? My
understanding is that Spice uses an Ebers-Moll (sp?) simplification to model
some of the physical properties of a transistor. Does this model include
capacitances such as the miller effect that I read about in some of the
discussions?

Also, do the LTSpice and Circuitmaker models use the Spice models in the AC
analysis or some other small signal simulation (e.g. y parameters or h
parameters)?

Thanks,
C
 
J

John Popelish

Jan 1, 1970
0
cledus said:
All,

I found the discussions regarding Paul Burridges' FSM design very
enlightening. I have a tangential question, though. Does Spice (LTSpice,
Circuitmaker, etc.) accurately model transistor operation at 40 MHz? My
understanding is that Spice uses an Ebers-Moll (sp?) simplification to model
some of the physical properties of a transistor. Does this model include
capacitances such as the miller effect that I read about in some of the
discussions?

Also, do the LTSpice and Circuitmaker models use the Spice models in the AC
analysis or some other small signal simulation (e.g. y parameters or h
parameters)?

It certainly models much of the influence of junction capacitances,
but neglects lead and trace inductance, propagation delay and
capacitance, unless you add these in as extra components. I think it
is probably pretty good at 40 MHz, but less so at 400 MHz (for the
neglected things listed, above).
 
J

Jim Thompson

Jan 1, 1970
0
It certainly models much of the influence of junction capacitances,
but neglects lead and trace inductance, propagation delay and
capacitance, unless you add these in as extra components. I think it
is probably pretty good at 40 MHz, but less so at 400 MHz (for the
neglected things listed, above).

Assuming that the "model maker" knew what he was doing, Spice models
are *very* accurate. However, unless you get a subcircuit model such
as Motorola used to provide for their RF transistors... which included
*package* parasitics, the accuracy will fall apart, probably in the
hundreds of MHz range.

...Jim Thompson
 
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