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Design >> RF Design >> variable Vth
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Message started by jason_class on Aug 19^th, 2005, 7:14am

Title: variable Vth
Post by jason_class on Aug 19^th, 2005, 7:14am

Hello All

Could anyone tell me why cmos circuit with variable Vth is considered an advantage for low power technology?

Kindly advise.
Thank you

best regards
Jason

Title: Re: variable Vth
Post by svensl on Aug 19^th, 2005, 9:31am

I think the main advantage of using multiple thresholds is that they can achieve low power and high performance while maintaining low leakage current.
As far as I know you could use high threshold transistors to suppress the subthreshold leakage current, while the low threshold transistors could be used to achieve the high performance. But I am not very knowledgeable on that topic.

Title: Re: variable Vth
Post by jason_class on Aug 20^th, 2005, 1:14am

Hi Svensl

That's right. Thank you
But any idea how cetain parameters is changed or manipulated to get a complex system where we have the Vt varied for certain applicatons?
How would this attempt complicate the whole system and what is the trade off?
Thank you all

jason

Title: Re: variable Vth
Post by svensl on Aug 20^th, 2005, 2:26am

I am not sure how to do that. I would have to study papers first in order to get familiar with that topic, such as
"Low Voltage Low Power CMOS Design Techniques for Deep Submicron ICs" by Vivek K. De
http://ieeexplore.ieee.org/iel5/6598/17617/00812579.pdf?tp=&arnumber=812579&isnumber=17617

Maybe someone else from the forum knows.

Title: Re: variable Vth
Post by jason_class on Aug 21^st, 2005, 5:36am

Yes checking out the paper from you Svensl
Let's see if anyone has any idea

will write back again

jason

Title: Re: variable Vth
Post by ssupin-ma on Aug 22^nd, 2005, 4:23pm

Without going into too much detail, lower the supply voltage can reduce the power consumption. And to make a digital gate can recognize the "1" and "0", we need lower Vt MOS device. But the I/O require higher signal level to overcome the environment noise (and parasitics), so we need multi-Vt process as a low power MOS process. That we can keep the core circuit runing with low vt device with low supply voltage, and I/O with high vt devices.

In some advance process (90nm and beyond) the off leakage current become important. Some circuit will use a medium/high vt device to turn off the supply voltage of part of circuits when we don't using it. And some circuit can story some data from low vt RAM to some high vt RAM and shootdown the low vt RAM when we are not exchange the data. And re-store the data back to low vt RAM when we need high speed operation.

Title: Re: variable Vth
Post by Geoffrey_Coram on Aug 25^th, 2005, 10:44am

Didn't Intel have some report on how they varied the body voltage of a MOS transistor to get its threshold voltage to vary?

Title: Re: variable Vth
Post by jason_class on Aug 27^th, 2005, 6:24am

Thanks everyone for the clue.