LM7171: LM7171 input bias current compensation

Hello Iwata,

You can follow the method described in this article: https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/04/11/input-bias-current-cancelation-resistors-do-you-really-need-them

This way both inputs will see the same resistance, and the voltages caused by the bias current will cancel each other. Note that both bias currents will not be exactly the same and you will still get some error because of this. You can look at the input offset current parameter to see the maximum difference between both bias currents. 

Best,

Hasan Babiker 

Yes, but this particular part has a high transconductance input stage where the the Ios is not much lower than the Ib (not matched that well). 

Getting that high FPBW with good DC precision is a challenge, might publish an article on how to do that someday. 

Michael-san,

Thank you so much for your comment!
I agree with you.

Hasan-san,

Thank you so much for your support.

I can understand what Bruce-san pointed out for the precision amplifiers.
While, I would like to double-check in the case of LM7171.
As you know, the each input of LM7171 is constructed with "diamond buffer" and each buffer drives the same load "RE".
In my understanding, the input bias current (especially its flowing direction) for diamond buffer is depending on its loading current, i.e. the direction of the each input bias current is opposite each other.
Therefore, the simple compensation circuit in the case of precision amplifier, such as "Rb", is not effective to LM7171, i.e. on the contrary to the case of the precision ampilier(with long-tail pair input circuit) there is no appropriate bias compensation circuit for LM7171 or some high speed amplifier with the similar input structure (Buffer + RE + CFB amp constructed with wilson-type current conveyor).
Is my understanding correct?

Best regards,
Iwata Etsuji