ultra low power op amp

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geneiusxie

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Joined 2012
#1
Hi, what's the best ultra low power op amp for building an active filter and other miscellaneous audio signal processing? And I mean really really small amount of power, drawing <0.05ma. I'm not sure, but I think the slew rate and noise values are the things to look for in terms of audio quality. It also can't require more than 5 volts input, ruling out some JFET op amps. I think a current feedback amplifier might do the trick (they're definitely fast enough), but I don't see any of those drawing <0.05ma, the lowest I've seen on digikey, etc. draw 0.4 ma. Way too much current.

BTW, cost is not a concern, and complexity isn't that important either, I just need the best performance, in a very very small and energy efficient package. Surface mount components are a must.
 
#4
RJM1 said:
mic863 4.2μA supply current/channel
http://www.micrel.com/_PDF/mic863.pdf

MIC863YM8 TR Micrel Inc | 576-2934-1-ND | DigiKey
Click to expand...

Hmm I was thinking of something like this:

http://www.micrel.com/_PDF/mic862.pdf

-All of these amplifiers have a lot of noise - around 50nv/sqrt(hz). That's 10x more than more typical amplifiers, so log(10^2) = log(100) = +20db more noise than I'm used to. Are there any lower noise amplifiers in this power range or are they already near the fundamental limits of physics?
 
#6
50 nV/sqrt(Hz). That's 10x more than more typical amplifiers.
Click to expand...

Even with perfect bipolar transistors (zero rbb') a differential pair (i.e. the input stage of an opamp) with 5 nV/rtHz requires about 40 uA tail current. Go figure if you want to build an entire opamp with this amount. Also distortion of such ultra-low power amplifiers is bound to be mediocre, particularly at the upper end of the audio frequency range.

Take note that quiescent current is not the only thing to worry about. Load current will, unless this is a design with extremely high impedance loads, easily exceed the quiescent current.

Samuel
 
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