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Harry Holt

Donít Use the Resistor I Told You to Use

Harry Holt
LynnHavens
LynnHavens
5/9/2017 2:45:23 AM
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Thanks for the Resistor artilce.

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Scott Elder
Scott Elder
5/8/2017 12:51:54 PM
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Re: Are you sure?
Thanks for knocking this around Harry.  Should you change the part reference, you probably want to change the 1k to 50 ohms as well.  Nevertheless, thanks for sharing.

Scott

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Depoussierageind
Depoussierageind
5/5/2017 3:53:40 AM
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An unforgettable discovery
Fortunately that there are always good connoisseurs who always think about sharing with others

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opampguy
opampguy
5/4/2017 10:18:58 AM
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Re: Are you sure?
Scott,

  Thanks for the feedback.  I used the 741 for an example of IB and IOS.  I should have made it more clear that the examples are independent.  The total noise is of course a function of the noise gain, all the resistors, voltage noise of the op amp and current noise.  For a 741, the voltage noise of the op amp would dominate.   For an op amp such as the AD8597, you have to look at the all the noise sources.

Mini-Tutorial, MT-050 at www.analog.com goes into more detail.

Harry

 

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Scott Elder
Scott Elder
5/3/2017 1:19:14 PM
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Are you sure?
It seems your example assumes the resistor noise dominates.  In the case of a 741, the input referred noise is on the order of 60nV/rt Hz; over one order of magnitude higher than the 909 ohm resistor.  Hence it is the amplifier that sets the noise, not the resistor(s).  Most times this is the case if the amplifier is continuous time (i.e. not auto zero or chopper class).  If dc error is at all a consideration, generally I find it best to include the resistor.

Scott

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