cmos question

[[email protected]]

How do I calculate the drain length Ld of a nmos/pmos? In BSIM3V3,
there is no parameter Ld.. Can anyone suggest what I can do?

Thanks,
Megs.

 

[Kevin Aylward]

How do I calculate the drain length Ld of a nmos/pmos? In BSIM3V3,
there is no parameter Ld.. Can anyone suggest what I can do?

Width and length are user specified values. They are specified on the
net list line, e.g.

m1 1 2 3 nmos L=1.2u W=15u

Some spices (e.g SuperSpice) allow these parameters to be set on the
schematic via the GUI.

Ball park values for L and w are often designed from:

I=K.W/L(Vg-Vt)^2

More often, one just runs the sim a few times till the numbers are what
you want

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[[email protected]]

Thanks for your reply, Kevin.

Here, in the formula given above, L stands for length of the channel..
What I am trying to find out is the length of the drain (or source) so
that I can find the area and perimeter of the drain (and source) .....
In the tool LTSpice, I have to enter the area and perimeter of the
drain so that the tool can calculate the capacitances.



Meghana.

 

[Jim Thompson]

Thanks for your reply, Kevin.

Here, in the formula given above, L stands for length of the channel..
What I am trying to find out is the length of the drain (or source) so
that I can find the area and perimeter of the drain (and source) .....
In the tool LTSpice, I have to enter the area and perimeter of the
drain so that the tool can calculate the capacitances.



Meghana.

Look up HDIF. Generally AD, AS, PD, PS, NRD, & NRS are all calculated
from L, W & HDIF.

...Jim Thompson

 

[[email protected]]

Thanks for replying, James. But here is no HDIF in LTspice (Swcad
III)...

Meghana.

 

[Jim Thompson]

Thanks for replying, James. But here is no HDIF in LTspice (Swcad
III)...

Meghana.

It's in the device model.

...Jim Thompson

 

[Kevin Aylward]

Look up HDIF. Generally AD, AS, PD, PS, NRD, & NRS are all calculated
from L, W & HDIF.

Yes I missed that point of the post. I have the formulas for the above
in my SS help file. Of course, in SS you don't need to, its all
automatic!

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.