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# What is the input impedance of AD8609?

Planning to use AD8609 for pH application, which needs an amplifier with very high input impedance and low bias current. Couldn't find the impedance information in AD8609 datasheet.

Parents
• Hi Hasan,

I have this plot of the AD8609 Ibias vs Vcm at 125C.

Based on the scope of these plots, we can get an idea of the worst case input impedance of the device. Taking data from one of the plots will give,

R(cm) = (4.5-0.5)/((370-270)E-12) = 40Gohms

Does that help?

May I also ask what the major considerations of your design are? How important is power consumption in your design?

Thanks,

Kris

• Hi Hasan,

I have this plot of the AD8609 Ibias vs Vcm at 125C.

Based on the scope of these plots, we can get an idea of the worst case input impedance of the device. Taking data from one of the plots will give,

R(cm) = (4.5-0.5)/((370-270)E-12) = 40Gohms

Does that help?

May I also ask what the major considerations of your design are? How important is power consumption in your design?

Thanks,

Kris

Children
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