Difference in gm and Id values obtained in hand calculation and simulation results ?

Presumably your hand calculations were incorrect then.

Most likely you've used far too simplistic equations in your hand calculations. Most text book MOS equations are not correct for any current technology (they weren't accurate even 25 years ago, so with 180nm they wouldn't be either).

Andrew

Presumably your hand calculations were incorrect then.

Most likely you've used far too simplistic equations in your hand calculations. Most text book MOS equations are not correct for any current technology (they weren't accurate even 25 years ago, so with 180nm they wouldn't be either).

Andrew

Thank You sir,

I used the following formulas for hand calculations,

Id=0.5 * Un Cox * W/L (Vgs-Vt)^2

gm=2Id/Vgs-Vt

Un = 3.5 E^-2

Epsilon r = 3.9

Tox= 4*E^-9

Are these equations and values correct or is there a change needed in them ???

Is there any way/formula to calculate these values by hand ?

The textbook equations are reasonable for a first stab and to get a good understanding of the first-order way that transistors work and trends (so the broad relationships between currents and voltages), but there's very little point in doing detailed hand calculations and comparing against simulation. This is what simulators are for and are good at.

You could look through the model equations for the device models used - e.g. bsim3 and bsim4 (depends on the model files being used) which will give you the more detailed equations that are actually used. You can see these in the Spectre Circuit Simulator Components and Device Models Reference manual (in <SPECTREinstDir>/doc/spectremod/spectremod.pdf - also accessible via support.cadence.com and using cdnshelp. There are text books too which cover this - for example, I have a copy of MOSFET Modeling with SPICE by Daniel P Foty (there are definitely more recent texts - I found quite a few when doing google search). However, I rather doubt you want to go to the level of hand-calculating these more complex equations used in modern MOSFET models when you can have a computer do it for you.

Regards,

Andrew.

Thank you sir...!!!