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LMH6629: How to Test performance of a TIA/ How to emulate a photo diode in LAB

Shyam Daram
Expert 1225 points
Part Number: LMH6629
Other Parts Discussed in Thread: OPA857

Dear TI,

After going through Application Note SONOA942


We have selected LMH6629 as one of the IC for our TIA or I-V  application, we are verymuch interested in testing its performance and also want to emulate photo diode, we want to give input to this TIA and see the output whether its able to process our narrow pulses ranging PW 30ns PRF 1Khz


Kindly provide us proper lab setup for testing these TIAs, initially we thought of testing it by making use of pulsating voltage source with a series resistance to create a current source of requirement, as the current to be tested are as low as nA, we are not sure about the capacitve effects that would be added to the TIA at input due to high resistance

Kindly let us know what kind of setup TI would suggest to emulate photo diodes exhibiting characteristics like 10nA-100mA of current and PW of 30ns and PRF of 1KHz

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    TI__Genius 12631 points

    Hello Shyam,

    We have been using a real photodiode to test the performance of our amplifiers in a TIA configuration recently. We excite it with a pulsed laser diode and use an optical attenuator to control the incident power on the photodiode.

    See the following reference designs with the OPA857:

    Another possible method is to configure the amplifier as an inverting attenuator. It is important that it be configured as an attenuator such that the gain resistor is at least 10x-100x larger than the feedback resistor. Also, be sure to add a physical capacitor to match the capacitance of your photodiode right at the amplifiers inverting input. The key here is to configure the circuit such that the noise gain response shape would closely match that of the TIA configuration. Along, the same lines here is another article that would be insightful in TIA testing.

    -Samir