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AD8000: Biasing the non-inverting input

Question asked by ajupic on Jun 6, 2017
Latest reply on Jun 7, 2017 by ajupic

Hi,

 

I'm using AD8000 as a single-supply AC coupled non-inverting amplifier; the circuit configuration is shown in the attached image.

Input signal is a 300kHz pulse with an amplitude of 200-250mV. The gain of the amplifier is ~5.75. The accuracy of the output signal is not all that critical. 

I am biasing the non-inverting input at 1.6V using a ultra low noise voltage regulator. 

Here is my question: since AD8000 is a current feedback amplifier and hence the input bias currents are unmatched/not equal, what value of bias resistor, R2 in the attached image, should I use? Do you have any recommendations? Should I also be adding an additional series resistor on the non-inverting pin?

 

Additional info:

A value of R2=4.99k in the simulation results in the output of the amp being offset by exactly 1.6V. Increasing R2 results in offset lower than 1.6V, while lower values of R2 result in an offset higher than 1.6V.

I've used values of 10k and 357 Ohm for R2 (= Rbias) in the physical circuit with satisfactory results.

 

Thanks,

Aki

 

 

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