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

Aalelai

Hi,

I simulated a nmos in 180nm technology and found its parameters. The hand calculated values for gm and Id were not same as simulated values (different Vgs values were used).

Specs: Vdd = 1.8V; W=420nm; L=180nm; Vds=0.9V. 

Parents

  • 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

  • in reply to Andrew Beckett

    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 ???

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