ADN2873 Ibias and Imod

Dear all

I have very simple question about ADN2873.

Could you give me your support?

(Is it OK to write the topic of this device in this place/category? Or couldn't you support this IC?)

Ibias and Imod, the current paramaters are written in the datasheet, can these be regards as the current which flow throught PD and LD?

Best regards,

  • Dear Customer,


    IBIAS and IMOD are not 100% the DC/AC currents delivered to LD.

    Instead, IBIAS current is the total DC current ADN2873 sinks. The majority of IBIAS current is from LD DC current and a small fraction of the DC current is from the external (compensation) circuitry (if you select a compensation pull up resistor) of the datasheet recommended AC coupled laser interface.


    IMOD current is the total AC current ADN2873 sinks. IMOD might be composed of the AC current through the (pull up) termination resistor and through the equivalent AC load (laser diode + serial damping resistor).


    None of the BIAS and IMOD current pass through the MPD. MPD current is a photocurrent generated by MPD, triggered by laser optical laser power. Depends on the optical coupling factor between LD and MPD, the MPD photocurrent is usually proportional to the IBIAS current, given the optical coupling factor keeps in a linear range,


    Hope these are useful information to your questions.


    Best Regards,


    Dongfeng Zhao

  • Dear Dongfeng Zhao

    I investigated IBIAS and IMOD using ADN2873 Evaluation board.

    Please check attached excel file.

    Moduration current vs. Total supply current result is almost same as ADN2873 datasheet.

    However I use the LD; MITSUBISHI ML720K19, absolute maximum rating power is 10mW.

    Assuming that this test result is correct, the LD may be shoot by over power/current.

    Is this phenomenon reliable?

    Best regards,

  • Dear Masuda-san,

    Firstly, have you checked the Ith and slope efficiency of the laser ? Ith = 5mA and 0.35mW/mA are datasheet typical numbers (in its linear range).

    Secondly, have you checked the optical average power vs. variant IBIAS current settings at the laser side?

    This experiment could give you a sense of linear range of the laser slope efficiency.

    Thirdly, ADN2873 uses AC coupling interface from LDD to LD, so the power vs. operation currents

    would give P1(Ibias + Imod/2), and P0(Ibias - Imod/2). Given the laser operation currents are in the slope efficiency range, you might calculate the P0 and P1 with the datasheet promoted slope effciency number, or

    you have to use the compressed slope efficiency number to get a better P1/P1 power estimation.

    Please note, at the laser compressed range, the slope efficiency may be smaller than typ. number

    the datasheet promoted.

    Hope these are useful to your investigation. Thank you for being interested in our ADN2873.

    Best Regards,

    Dongfeng Zhao

  • Dear Dongfeng Zhao

    I'm sorry for my late reply everytime and thanks for the lecture and support.

    Current situation, we use MITSUBISHI LD ML720K19S, however it is not recommended by ADI.

    And our current schematic is attached figure, "Differencial" schematic.

    Perhaps you will find that RCL value is not proper soon, and it may be disproper schematic.

    However the "Differencial" schematic achieves high frequency operation; ~2GHz.

    I hope below statement;

    "When use this EVALZ-ADN2871/ADN2873 board to evaluate other differential lasers

    LDs, one optimization work is necessary on the circuitry between the DUT to the LD.

    Please contact ADI sales for the necessary technical support."

    It is written in ADN287x EVB Application note.

    Could you tell me advise for correc design?

    Thanks and best regards,

  • Dear Masuda-san,

    Are you located in Japan? If yes, would you please contact our sales office for further support?

    Our ADKK (Japan Sales Office) contact number is: 81-3-5402-8200.

    Best Regards,

    Dongfeng Zhao