[LTspice] Why does NMOS netlist with 4 nodes?

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!

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_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
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Netlists as

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

...Jim Thompson

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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

Hello Chris,

Substrate?

Regards, Joerg

"Chris Carlen" schrieb im Newsbeitrag news: snipped-for-privacy@news4.newsguy.com...

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