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LMH34400: Sensing Photodiode without Bias

Kei Kuwahara
Expert 5740 points
Part Number: LMH34400

Hello team,

My customer would like to sense photo diode (transimpedance circuit) with single supply OPAMP.

However, if the Opamp is operated with single supply, it will require bias voltage because if the photo current = 0A, then the output will be out of comon mode range.

I have found LMH34400, and it is single supply, no Bias voltage needed for transimpedance operation.
Is this device usable without any bias for Photodiode? On the datasheet, the Kathode of photo diode was connected to -Bias voltage.

Can LMH34400 operate with wy customer's photo current spec below?

  • 50nA max
  • 10pA at dark current
  • Few kHz frequency pulse current

Best Regards,
Kei Kuwahara

  • 0
    TI__Expert 6050 points

    Hi Kei,

    Unfortunately, I do not believe the LMH34400 will be a great choice based on the customer photocurrent specifications. The LMH34400 has a transimpedance gain of 40kohm (assuming a 100 ohm load) which would lead to an output voltage swing of 2mV at the maximum photocurrent. This is very small and easily susceptible to noise. You will need a TIA that has a much larger gain.

    Can you share the reason for not wanting to include a bias voltage on the noninverting pin of an amplifier configured as a TIA?

    Thanks,

    Nick