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multisim mosfet B170 worng defined report



In the BS170 model, the Cgdo is defined as 3pF. The default width in MS11 is 0.0001 m that scales down this value.

The model should be updated to:


or default W in interactive sim settings -> custumize -> device should be set to 1m.


Maybe this can be found in other mosfets.





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Hello Jeffrey,
Thank you for reporting a potential problem in Multisim. I am not the expert on this topic, but I found an older Spice model (from 2000) where the BS170 MOSFET is modelled the same way as in Multisim v13.0:


*ZETEX  BS170 Mosfet Spice Subcircuit   Last revision  12/85
.SUBCKT BS170/ZTX 3 4 5
*                 D G S
M1 3 2 5 5 N3306M
RG 4 2 270
RL 3 5 1.2E8
D1 5 3 N3306D
.MODEL N3306M NMOS VTO=1.824 RS=1.572 RD=1.436 IS=1E-15 KP=.1233
+CGSO=28E-12 CGDO=3E-12 CBD=35E-12 PB=1
.MODEL N3306D D IS=5E-12 RS=.768




I am not sure if the standard width for MOSFETS in Multisim (100um, as you already indicated) is directly applied to the size of the Gate-Source and Gate-Drain overlap capacitances, I will have to consult a colleague.

Kind regards,
Jos Deurloo
National Instruments
Applications Engineer


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Hi, I have a similar problem, How did you find the value of Length or Width. Becuse I could not find them in the library of BS170. It is important for me to find these values to calculate the K value . 

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