# can dummy transistor AD=0 or AS=0?

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#### angela.green

##### Newbie level 3
hi,
might be really silly question to some of you. when will dummy transistor's

Area of drain =0 or Area of Source=0

I know dummy transistor are shorted, but in what kind of situation will the above appear?

Thanks

can anyone help me on this? Would be sooooooooo............thankful!

if the areas of the drain and source are 0, you have two possibilities: there is no transistor or you are using some default values.

I always see these defaulted to 0 in my PDK, but there
are params for the LD/LS and deltas, and W of course
is known so Spectre can calculate the areas and peripheries.

thank first for you guys' answer. but actually I want to know when will IN_S==0 or IN_D==0 in the following calibre xrc extraction. Someone told me that it happened when it has dummy transistors, but how come IN_D =0? Is it for the dummy transistor? or is it happened for normal transistor? Thanks again!

DEVICE MP(P) pgate POLY PSD PSD WEL <PDIFF>

DMACRO MOSPROP DEVICELAYER PIN AUX1{
W=PERIMETER_COINCIDE(DEVICELAYER,PIN)/2
L=AREA(DEVICELAYER)/W
IN_D=PERIMETER_INSIDE(D,AUX1)
IN_S=PERIMETER_INSIDE(S,AUX1)
IF(IN_S==0){
PD=PERIMETER(D)*W/IN_D-W
PS=PD
}
ELSE
IF(IN_D==0){
AS=AREA(S)*W/IN_S
PS=PERIMETER(S)*W/IN_S-W
PD=PS
}
Else{
PD=PERIMETER(D)*W/IN_D-W
AS=AREA(S)*W/IN_S
PS=PERIMETER(S)*W/IN_S-W
}
]
}

It depends on how the PERIMETER_INSIDE function is defined. If layer AUX1 is missing, it might return a 0, but I am just guessing here...

the perimeter_inside is the standard Calibre's build-in function

The format is:
PERIMeter_INside(pin-or-layer, pin-or-layer)
Returns the total length of the parts of perimeters on the first pin
or layer that lie strictly inside shapes of the second pin or layer.

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