cmos question

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

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

Meghana.

It's in the device model.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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 snipped-for-privacy@anasoft.co.uk

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 snipped-for-privacy@anasoft.co.uk