[LTspice] Why does NMOS netlist with 4 nodes?

[Chris Carlen]

Hi:

The symbol nmos.asy included with LTspice only has 3 pins, yet this
symbol when included in a schematic netlists with 4 nodes.

Why is this?



Thanks.



--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Joerg]

Hello Chris,

The symbol nmos.asy included with LTspice only has 3 pins, yet this
symbol when included in a schematic netlists with 4 nodes.

Why is this?

Substrate?

http://nina.ecse.rpi.edu/shur/remote/NMOS_extract.html

Regards, Joerg

 

[Chris Carlen]

Hello Chris,


Substrate?

http://nina.ecse.rpi.edu/shur/remote/NMOS_extract.html

The M Spice primitive certainly has 4 terminals. But LTspice has both a
3-terminal and 4-terminal MOSFET symbol. The 3-terminal symbol netlists
4 nodes. I am simply curious as to how this occurs, since it is
inconsistent with the symbol's 3 terminals.


Good day!




--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Jim Thompson]

The M Spice primitive certainly has 4 terminals. But LTspice has both a
3-terminal and 4-terminal MOSFET symbol. The 3-terminal symbol netlists
4 nodes. I am simply curious as to how this occurs, since it is
inconsistent with the symbol's 3 terminals.


Good day!

Netlists as

MN1 %d %g %s %s ModelName L=...

...Jim Thompson

 

[Helmut Sennewald]

Hi:

The symbol nmos.asy included with LTspice only has 3 pins, yet this symbol
when included in a schematic netlists with 4 nodes.

Why is this?



Thanks.

Hello Chris,

This fourth pin is normally connected to the substrate of a
monolithic MOSFET.

LTspice automatically connects this 4th pin to the source in the
netlist even when only a 3-pin symbol is used for a MOSFET.
It's simply convenient to always have the same syntax in the netlist.

The 3-pin symbol is intended for VDMOS and other MOSFETs with 3 pins.

There is also a 4-pin MOSFET symbol in the components library
especially for monolithic MOSFETs.

Best regards,
Helmut

 

[Jonathan Westhues]

LTspice automatically connects this 4th pin to the source in the
netlist even when only a 3-pin symbol is used for a MOSFET.
It's simply convenient to always have the same syntax in the netlist.

I notice that it only does that when the symbol is netlisted with an `M'
prefix; if I use an `X' prefix then it netlists with only three terminals,
which is exactly what is required to run most subcircuit FET models.

Jonathan