questions about MOS in weak inversion region!

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jimmyshu

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weak inversion id0

I'm designing low power circuits,the current each branch is about several decad or hundred nA. i think it can be generated by biasing MOS in weak inversion region. The simplified formula in weak inversion region is as follows: id=(w/l)*Id0*exp{vgs/[n*(kt/q)]}, so if know factor n and Id0, it is easy to get id by hand. But I use BSIM3v3 for simulation, and the model don't give these two parameters. So the question is how to get n and Id0 from BSIM3v3 model? Or is there any way to caculate id in weak inversion region by hand using BSIM3v3 model parameter.
Thanks!
 

Do you really need to do hand calculation? If hand calculation is not really important to you, how about you try to obtain the desired current straight away from simulation. By biasing it at weak inversion, varies the ration of the transistor. start with single transistor 1st. then you get the rythm when you go for larger circuit. what process technology that you use? 0.18µ process?
 

Thanks so much for your advice! I'm a beginner and inexperienced. In the textbooks authors said that the first design step was to do hand calculation before computer simulation. So I always try to do hand calcution, and I think it's a good way to obtain design intuition. I'm using XFAB 0.6u process.
yesterday I've found a paper about how to extract hand calculation parameter for mos in weak inversion operations from BSIM3v3 model. It's useful to me.
Thanks anyway!
 


hi jimmyshu

Would u like to show me the paper! Very thanks
 

This is the paper including a method to exact hand calculation parameters in weak inversion operation from BSIM3 model.
 
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    echeee

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bias the mos in weak inversion region and simulation
 

weak inversion operation is not recommand, because the noise margin gets very low...
 

You can just used the simulation method to extract the param,may be just adding some mathematic pocessing.Be sure that the data of MOSFET also been chosen from the "saturation" region in weak inversion operation.
 

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