how to test the AD8605 as TIA (I to V) design using current source?


I am trying to test the Trans-impedance amplifier design using AD8605 for the photo-diode application circuit.

currently i am using an NI 9265 module to generate current source up to 20mA in my setup 

below is my circuit:


when i try to set the current to 500 micro Amps from the sources and feed to inverting terminal of AD8605; the output voltage of I-V amp is in few millivolts (~14mV).

But actual result is expected to be saturated at high level 3.3V.

is this correct or i am doing something wrong ?

please provide me the way to test the Trans-impedance circuit output with the current sources(micro amps range).

thank you,


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  • Hi Mani,

    Solving of this problem depends from tolerance and value of current which you need. As start, you can try high-ohm resistor and external voltage source in series. 

    Transimpedance amplifier has low input impedance, which equal Feedback resistor value divided by (1+Aol), here Aol is open-loop gain of op-amp. Therefore, input current will be equal External voltage divided by (External resistor plus inpur resistance of TIA). Keep the right current direction - from TIA input.

    I hope that this help you.