[sdiy] Resistors in feedback loop of noninverting op amp buffer

[Seb Francis]

Donald Tillman wrote:
>    > Date: Sat, 22 Nov 2008 10:24:46 +0000
>    > From: Seb Francis <seb at burnit.co.uk>
>    > 
>    > Donald Tillman wrote:
>    > >    
>    > > That feedback resistor is to insure that any voltage drop due
>    > > to the input bias current times the input resistance at the
>    > > positive input is roughly equal to the voltage drop due to the
>    > > input bias current at the negative input.  So it corrects for
>    > > any offsets due to input bias current.
>    > 
>    > So it's the same reason as for putting an input resistor on the -ve 
>    > terminal in a normal non-inverting amp configuration.
>
> Yes, indeed.  (Uh, you mean the "+" input terminal.  For both the
> classic inverting or non-inverting cases.)
>
>    > > The resistor is not necessary for FET input opamps.
>    > 
>    > And I guess the same is true for using an input resistor on the
>    > -ve terminal - this is also unnecessary for FET input opamps.
>
> Yes, that's right.
>
>   -- Don
>
>   

Sorry, yes.  Of course I meant +ve both times, not -ve!

Seb