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Low current increase the noise

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bicave

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When reading a document, it say that
" low current increase the noise" ? I don;t know the reason and
what else effect to the noise.
 

naalald

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Hi,
Of course it depends on the circuit. But in SC circuits as current decreases you should decrease the capacitor value to maintain the speed. So, the KT/C noise increases.
 

A.Anand Srinivasan

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maybe the author would have talked about the noise to signal ratio....
it would be better if you quote the whole text or mention the book and page number...
 

kobeghost

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for the thermal noise I think it will decrease with the current decrease,considering its key factor Gm.as for the 1/f noise,it is determined by the WL
 

tia_design

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It depends, for CMOS op amp, high current for input pair will reduce the noise, oh, what I said is not correct. Increasing current of input pair will increase both thermal noise and Gm, but for thermal noise, its gain is increased by √2, while for signal, the gain is increased by 2. Compare with each other, the noise is reduced. We often talk about input referred noise
 

lladnar23

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That's right -- in terms of thermal noise, you typically have to burn 4x the power to get a 2x improvement in SNR
 

A.Anand Srinivasan

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lladnar23 said:
That's right -- in terms of thermal noise, you typically have to burn 4x the power to get a 2x improvement in SNR
can you please brief what you mean by that... which power r u talking about increasing to increase the SNR....
 

alasliu

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input pairs thermal noise is 4kTr/gm. so if you increase current, gm ascend. thermal noise will be reduced.
 

leo_o2

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It is 4KT(2/3gm) for MOSFET.
 

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