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I am trying to further understand the .cir file I have downloaded from Infineon that I am using to model some of their mosfets in LTspice.

In the below example can anyone explain the lines starting with X$M? I can't find this format in any notes elsewhere

enter image description here

(note: Z27 and Z28 are other .subckt functions in the same .cir file)

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It could be that it's just an atypical character that's used simply because it's allowed and it stands out. The line starts with X, which is the designator for subcircuit. Whatever characters follow afterwards have to meet one single criterium: they have to be allowed by the parser (i.e. no errors should appear, the circuit should run).

$ and the M afterwards might suggest that it's an artifice simiar to what LTspice does when it substitutes elements, behind the scene. For example using [Misc]/Epoly with the FREQ keyword (bogus example):

E1 out 0 FREQ {V(in)} (0,0,0) (1,1,1) (2,3,4)

makes the expanded netlist to show up this line:

B§E1 out 0 V=V(in) FREQ (0,0,0) (1,1,1) (2,3,4)

So in this case it might be that some MOSFET (which M designates) might be involved, as in there was a schematic which had a subcircuit mimicking an MOSFET (it had the designator M), but LTspice detected it's not a .model and, when the general subcircuit was created, someone replaced the § with the $. The not labels seem to agree. It could be, it could be not. But the end result is that it's an allowed character and can be safely used; nothing to worry about.

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