AD8655: Current noise density

Q 

I couldn't find the information about the input current noise characteristics
(?fA/?Hz ) and input impedance characteristics of AD8655/8656 on the website
and also on the data sheet. How can I achieve this information?

 

A 

We do not measure current noise density for our CMOS parts since it is too low
and very difficult to measure. Theoretically, our spot noise for CMOS parts
around 10Khz is in tens of fA/rtHz and could be in low hundreds of fA/rtHz at
lower frequency. Based on design simulation, the current noise floor is around
2.5fA, but if you are using large resistors, then the noise of the resistor may
dominate
Comments
Anonymous
  • on Jul 13, 2017 5:31 PM

    • A current noise of 'tens of fA/rt-Hz' is not so low.

      For AD8065 you declare a current noise of 0.6fA/rt-Hz, more than an order of magnitude lower.

      It is very useful to add this information in the datasheet of AD8655: if someone want to use this operational amplifier in a trans-capacitance configuration, e.g. for the readout of a MEMS sensor, the current noise contribution can easily dominate!

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