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sub voltage reference

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Blackuni

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Hi,

I am interested in designing a low voltage(<1v) reference. I have gone through several tech. papers, discussions in this forum and have an idea in general. But they donot have the equations based on which the dimensions of devices are decided.

Most of papers claim that to get noise improvement L & W values are large. how? upto my knowledge the L value is kept to process min. length and W value is varied.

Please help me with your inputs, references & real time examples

Thanks
 

Blackuni said:
Hi,
Most of papers claim that to get noise improvement L & W values are large. how? upto my knowledge the L value is kept to process min. length and W value is varied.
Thanks
Click to expand...

i'm a bit confuce about your statement. you said "..L value is kept to process min." then you said ".. length and W value is varied". L ≠ length?

In analog you shouldn't use minimum L size. use 3 -4 time bigger. But sometime you need to use even bigger L size. If you need to design for low power, you should try to bias your transistor in subtreshold region. low current means low voltage required. hope it help a bit.

-evilguy-
 

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    Blackuni

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For low noise, you need a big transistor area. As evilguy points out, a design doesn't always use the minimum length for several reasons: 1. mismatch (see Pelgrom's paper), 2. Noise (look at any text on mosfet noise), or 3. need a higher intrinsic gain.
 

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    Blackuni

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Noise usually includes two different types: device noise and environment noise.
Device noise depends on device demension.
One of important device noise is flicker noise.
Vn²=K/(Cox.W.L.f)
So you can observe: if the transistor demension is increased, the noise will be reduced.
 

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    Blackuni

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