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in-amp biasing concern (3 op-amp config. using ADA4817-1/2)

Question asked by jawa on Jan 5, 2012
Latest reply on Jan 6, 2012 by jawa



I plan to build a high speed three op-amp in-amp like the one presented in the ADA4817-2 datasheet (figure 53 on page 21). The input will be only one coil that is connected between both inputs. The input signal to the in-amp will therefore be the voltage induced in this coil.


The question is now, if there is a need for an additional dc bias current path at both noninverting inputs of the op-amps (to GND?) or if it is sufficient that both inputs share the dc current path presented by the coil connected between them?


I want to avoid additional resistors at the inputs because they would need to have high ohmic values and therefore create a lot of additional Johnson noise. The only other possibility of dc-biasing I can think of at this moment would be a tapped coil with a connection to GND but this is not possible with the coils I am using.


Many thanks in advance for your help.