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Design >> RF Design >> help on second order effect!
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Message started by kibby on Oct 23^rd, 2009, 8:21am

Title: help on second order effect!
Post by kibby on Oct 23^rd, 2009, 8:21am

if the function of mos fet in saturation region is used:
i=1/2*ucw/l*(vgs-vth)^2
which ignore the second order effect;
to analyse the character of gm''(the second derivative of gm) of a simple full differential amplifier,then is the result helpful for design? or it is unreasonable?
why?
thx~

Title: Re: help on second order effect!
Post by Riad KACED on Oct 23^rd, 2009, 10:42am

Hi Kibby,

Yes, this is a reasonable approach for hand calculation. This is the way every designer goes calculate the first-step transistors. The second stage is to run a Spice level simulation, using Spectre, Eldo, Hspice ... etc. Simulators using models like BSIM3/BSIM4/PSP DO NOT assume any approximation at all, they give you the 'exact numbers' which are likely to be different from your hand-calculation.

Cheers,
Riad.

Title: Re: help on second order effect!
Post by kibby on Oct 24^th, 2009, 4:23am

thank you for your help~