Hi all:
Regarding the following schematic:
I've seen many schematics that have suggested that the resistor in the non-inverting input should be equal to the parallel equivalent of the two resistors in the feedback network. In the case where my one of my feedback resistors is variable, what is the recommended value for the resistor in the non-inverting input assuming that it's fixed?
Thanks!
In a lot of cases, maybe most cases, you don't need R3. It only matters if the input bias currents cause a serious amount of DC offset error.
If that is the case, I'd go for nulling offset at the highest gain, I guess.
R3 will increase noise.
John
I generally agree that the resistor probably isn't necessary, particularly with modern op-amps having very low input bias currents. But if offset voltage proves to be a problem, it might be worthwhile including the resistor. R3 might want to equal the parallel equivalent of the two resistors on the inverting side of the op-amp at the mid-gain setting, or the most used gain setting, whichever gives the best results.
John Lark>
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