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LMH34400: Is this possible to use for a balanced photodetection?

Seongjin Bak
Prodigy 110 points
Part Number: LMH34400

Hi

I want to know that the TIA "LMH34400" can be used for balanced photo-detection.

Is it possible to use it in this application?

if possible, I would like to amplify the signals coming from a balanced photo-detector.

A balanced photo-detector has two photo-diodes which are connected in series.

Bias is applied to end of each photo-diode.

And the signal comes out from the point where two photo-diodes meet each other.

However, in the datasheet of LMH34400, the cathode of a photo-diode should be connected the TIA by layout recommendation.

Can this TIA LMH34400 receive the signals coming from a balanced photo-detector?

BPD info.

www.rp-photonics.com/balanced_photodetection.html

  • +1
    TI__Expert 6050 points

    Hi Seongjin,

    The LMH34400 can be used to amplify sourced input currents from photodetectors in either a sinking or sourcing configuration. The LMH34400 is optimized for photodetectors that sink current, however. This is why the recommended layout is the cathode connected to the input, but that is not a requirement.

    To note when the photodetector is sourcing an input current: The soft clamp is the active clamp, not the fast recovery clamp

    Please refer to Section 7.3.1 of the data sheet for more details on this or let me know if you have any other questions.

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    Prodigy 110 points

    Hi Nick Nauman,

    Thank you for your kind explanation.

    Your reply is very helpful to understand its properties.

    However, in my case, I can't judge whether it has a sinking or sourcing configuration.

    Because the bias of balanced photo-detection will be applied by its own power supplier.

    the link below is similar block diagram that I will use.

    www.ofcconference.org/.../579388-pr-pressRelease3.pdf

    The differential-ended output of TIA is only different.

    If you have any comments about this, let me know.

    Thanks,

    Seongjin Bak

  • +1 in reply to Seongjin Bak
    TI__Expert 6050 points

    Hi Seongjin, 

    It may not be necessary to identify whether the photodetectors are sinking or sourcing current. 

    What is important to note:

    • Ambient Light Cancellation (ALC) circuitry should only be used when sinking current. If it is unknown if the current will be sinking or sourcing, this should be disabled
    • The input protection soft clamp and fast recovery clamp are determined internally. If the current is sinking, the fast recovery clamp will be active. If the current is sourcing, the soft clamp will be active.

    I hope this provides some clarification

    Thanks,

    Nick