• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 569 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ONET4211LD: BIAS pin processing

yoshihito takahashi
Prodigy 180 points

Part Number: ONET4211LD

ONET4211LD data sheet


Page 17 I have a question about Figure 25.


There is an inductor mark between the BIAS pin and the LD cathode.


What does this mean?


again,
”APC loop instability can occur with large inductive loading on the BIAS pin. To ensure loop stability in this case, it
is recommended to connect a 1-nF capacitor to ground at the BIAS pin ”


Is it okay to insert a 1nF capacitor between the BIAS pin and GND as described in?


If you have any necessary external parts such as the above capacitors that are not shown in Figure 25, please let us know.

  • 0
    TI__Guru* 93570 points

    Greetings,

    The APC loop can be stabilized under all conditions using an external capacitor. This capacitor should be connected between BIAS pin and VCC - in parallel with laser diode. The recommended capacitor value is 220nF.

    Perhaps you may need to add AC coupling capacitors based on common mode voltage and add 0.1uF Cap on to GND on PD pin.

    Regards,,Nasser

    Regards ,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 180 points

    Nasser san

    thank you for your reply.

    But I don't really understand the meaning of your answer.

    First of all, could you answer the following questions?

    -------------------------------------------------- --------------------------
    ONET4211LD data sheet
    Page 17 I have a question about Figure 25.
    There is an inductor mark between the BIAS pin and the LD cathode.
    What does this mean?
    -------------------------------------------------- --------------------------

    > The APC loop can be stabilized under all conditions using an external capacitor. This capacitor should be connected between BIAS pin and VCC --in parallel with laser diode. The recommended capacitor value is 220nF.

    ⇒Does the capacitor mentioned above refer to CAPC?
    According to the data sheet, the recommended value for CAPC is 200nF.

    > Perhaps you may need to add AC coupling capacitors based on common mode voltage and add 0.1uF Cap on to GND on PD pin.

    ⇒Which of the above-mentioned capacitors is an AC-coupled capacitor?
    Also, apart from the AC coupling capacitor, 0.1uF between PD pin and GND Does that mean you need to add more capacitors?

    Regards,  takahashi

  • +1 in reply to yoshihito takahashi
    TI__Guru* 93570 points

    Hi Takahashi-San,

    1). Ferrite bead on BIAS pin does not have any effect on DC bias current. This is done to provide a high impedance to the modulation current. This isolates modulation current from BIAS pin.

    2). This is different from CAPC. This is additional Cap between BIAS pin and Laser Anode/VCC.

    3). AC coupling Cap is on DIN+ and DIN- pins. This allows interface to different interface regardless of their common mode voltage.

    4). Yes it would be good to provide a provision for adding Cap between PD and GND. This attenuate potential noise on this signal.

    Regards,,Nasser 

  • 0 in reply to Nasser Mohammadi
    Prodigy 180 points

    Nasser san

    thank you for your reply.

    In this case, what is the recommended value (H) of the inductor (ferrite beads) between the laser cathode and the BIAS pin?

    Regards,  takahashi

  • 0 in reply to Nasser Mohammadi
    Prodigy 180 points

    I'm sorry often.
    The data sheet has the following description.
    "APC loop instability can occur with large inductive loading on the BIAS pin. To ensure loop stability in this case,
    it is recommended to connect a 1-nF capacitor to ground at the BIAS pin. "

    Does this mean that it is better to connect a 1nF capacitor between the BIAS pin and GND?

  • 0 in reply to Nasser Mohammadi
    Prodigy 180 points

    Nasser san

    Excuse me.

    I've made this thread "Resolved", so It may have been overlooked,

    so We will contact you again. Please tell me about the following two items.

    1. In this case, what is the recommended value (H) of the grating (ferrite beads) between the laser cathode and the BIAS pin?

    2. The data sheet has the following description.

    "APC loop instability can occur with large inductive loading on the BIAS pin.

    To ensure loop stability in this case, it is recommended to connect a 1-nF capacitor to ground at the BIAS pin. "

    Does this mean that it is better to connect a 1nF capacitor between the BIAS pin and GND?

    Please confirm.

    Regards,  takahashi

  • +1 in reply to yoshihito takahashi
    TI__Guru* 93570 points

    Greetings,

    1). The exact ferrite bead is determined based on the optical eye optimization. Ferrite bead that can be considered are: Murata BLM03HG102SN1D.

    2). Bias pin needs to be connected to AC ground. This means this Cap can go either to Vcc - connected to the anode of the laser diode - or GND. 

    Regards ,, Nasser

  • +1 in reply to Nasser Mohammadi
    Prodigy 180 points

    Nasser san

    thank you for your reply.

    Thank you for your kind support.

    Regards,  takahashi