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Design >> Analog Design >> Oxide capacitance question
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Message started by stephenry on Feb 20^th, 2006, 5:11am

Title: Oxide capacitance question
Post by stephenry on Feb 20^th, 2006, 5:11am

Hi all,

So, I'm pretty new to analog design, but I desperately want to get involved. I have the book by Razavi, and on page 37 he give some parameters for a 0.5um CMOS process (enough to simulate under SPICE LEVEL 1). The MOS parameters given in the book are: LEVEL, VTO, GAMMA,PHI,NSUB,LD,UO,LAMBDA,TOX,PB,CJ,CJSW,MJ,MJSW,CGDO,JS.

What I would like to do is, do some rudimentry calculations using the usual triode/saturation equations for the behaviour of MOS and then compare them to the figures I receive from the SPICE simulation. The question I have is how can I derive from these parameters, the value of Oxide capacitance (Cox - so that I can use the equations for the drain current in my calculations, i.e. id = UnCox(W/2L)(Vgs - Vtn)^2, etc... ). I know there must be an equation relating these parameters (as SPICE obviously does not just invent them from thin air) but I cannot find one in any of my books that would be suitable for a simple first order approximation.

Another question I have is: As a first project, and for someone with an interest in the field, what would be a good thing to design (i.e. not too easy and not too difficult)?

Any ideas?

Stephen

Title: Re: Oxide capacitance question
Post by Marc Murphy on Feb 20^th, 2006, 7:20am

Cox' = eox/tox (F/m^2)

eox is the dielectric constant of SiO2. It is 4 times the free space constant.

I would try simulating the examples from the book and understanding how they work.