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Input bias current issue with AD8065 example circuit.

Category: Software
Product Number: AD8065
Software Version: 24.0.12

I am simulating the example given in LTspice for AD8065. 
I practically clicked on the AD8065 symbol and then clicked on Open Example Circuit.

after running simulation I clicked to plot input currents to the AD8065. They show to be a sinewave of 10MHz frequency and an amplitude of about 100uA.

The datasheet of this JFET opamp considers it to be maximum 25pA.

What is the source of this discrepancy?

Dorin

  • The circuit is working as expected.  If you look at the AD8065 datasheet you'll see that the common-mode input impedance is 1M in parallel with 2.1pF.  At a frequency of 10M the magnitude of this impedance is 7.58K so 1 volt across this results in 132uA.  The simulation shows a current into the + input of approx. 120uA so the model agrees with the spec within reason.  Lower the frequency and you'll see the current decrease.  Run an operating point analysis and the currents into the OA inputs will be down into the pA range.