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ONET1101L: ONET1101L about the output pulse time

Mickey Zhang
Genius 12080 points
Part Number: ONET1101L
Other Parts Discussed in Thread: ONET1151L

Hi Team,

The customer is using ONET1101L. The customer cannot output more than a 5ns pulse. The input signal is a 20ns square wave signal. But  the maximum time for

the output waveform pulse is less than 4ns.  Then the customer adjusts the IBIAS current and the IMOD current, but the time for the output pulse is less than 5ns.

Q1: Can ONET1101L output a more than 10ns square wave pulse?

If it can, what are the reason for the customer's issue? How to solve the customer's issue?

If it cannot, can you recommend a suitable IC that can meet the customer's requirements?

Q2: The datasheet for ONET1151L shows it can "Pin-Compatible to the ONET1101L Device". What are the differences between ONET1101L and ONET1151L?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

  • 0
    TI__Intellectual 1715 points

    Hi Mickey,

    Ans to Q1) The ONET1101L driver is designed to operate for bit rates between 2 Gbps and 11.3 Gbps. 20ns square wave signal corresponds to 100 Mbps which is very low for this device. Our ONET laser drivers are designed for high-speed communications applications in Giga Hertz range, we do not have anything specifically designed for such low speed applications.

    Please suggest the customer to try our 4Gbps-capable laser drivers, for instance the ONET4211LD. This laser driver has been designed to operate between 155Mbps to 4 Gbps and should be able to go down to 100Mbps.

    Ans to Q2) ONET1151L is the next-generation laser driver to the ONET1101L, both designed for 11.3Gbps applications. ONET1151L differs from ONET1101L in that is provides additional output waveform shaping through Digitally controlled output De-emphasis (8 levels possible using 3-bit DE register) and output termination resistance options, which are not present in ONET1101L. Also, ONET1151L has slightly lower power dissipation and higher MOD output (of 85mApp compared to 80mApp offered by ONET1101L). 

    Hope that helps.

    Thanks,

    Sri

  • 0 in reply to Sriharsha Kota Pavan
    TI__Genius 12080 points
    Hi Sriharsha,

    Thank you for your reply.
  • 0 in reply to Sriharsha Kota Pavan
    TI__Genius 12080 points

    Hi Sriharsha,

    The customer has another two questions:

    Q1: The customer tests the DC-Coupled output and AC-Coupled output for ONET1101L. The test results show that the Imod of the DC-Coupled

    output is higher than the Imod of the AC-Coupled output. And the Ibias is lower of the DC-Coupled output than the Ibias of the AC-Coupled

    output. What is the reason for these two cases?

    Q2: Can the MOD pins output the DC signals like the BIAS pin? If DIN pins are input the DC signals, can the MOD pins output the DC signals?

  • 0 in reply to Mickey Zhang
    TI__Intellectual 1715 points

    Hi Mickey,

    Q1. Can you please ask the customer to provide more details on the output and input conditions for both DC- and AC- coupled cases? The ONET1101L is designed for the AC-coupling with the laser diode, and is supposed to provide higher MOD output when AC-coupled compared to DC-coupled case. 

    Q2. The DIN+/- pins are only AC-coupled input pins, so you can not input the DC signals.

    Thanks,

    Sri 

  • 0 in reply to Sriharsha Kota Pavan
    TI__Genius 12080 points
    Hi Sriharsha,

    Thank you for your reply. I will ask the customer this. Then I will tell you.
  • 0 in reply to Sriharsha Kota Pavan
    TI__Genius 12080 points
    Hi Sriharsha,

    Update:

    The customer test the DC- and AC- coupled cases are as belows:

    First, 0.1uF capacitance and 0 ohm resistance are connected to the output. Use single-ended output.

    Second, test the Imod values.
    a). Set the Ibias register values to be 0.
    b). Set the same Imod register values for the DC- and AC- coupled cases.
    c). Use the laser to output laser light. And then test the Imod for the DC- and AC- coupled cases.

    Third, test the Ibias values.
    a). Set the Imod register values to be 0.
    b). Set the same Ibias register values for the DC- and AC- coupled cases.
    c). Use the laser to output laser light. And then test the Ibias for the DC- and AC- coupled cases.

    At last, the test results show that the Imod of the DC-Coupled output is higher than the Imod of the AC-Coupled output. And the Ibias is lower of the DC-Coupled output than the Ibias of the AC-Coupled.
  • 0 in reply to Mickey Zhang
    TI__Intellectual 1715 points

    Hi Mickey,

    Thank you for the info. 

    The collector nodes of the output stages of the ONET1101L driver are connected to the output pins MOD, which are optimized for driving a 25ohm load. Please ask the customer to connect a 25ohm TL between the modulation pins and the laser diode.

    Also, for the Imod testing, if the laser Bias is set to 0, laser output is typically negligible (laser turned off). For accurate results, please ask the customer to operate at a typical Bias point for the laser. To be sure that the results are not impacted by the laser response, it would be best if the electrical output from the MOD pins of the ONET1101L are tested and compared directly between the two cases.

    The ONET1101L is designed to deliver higher modulation output when it is AC-coupled to the laser diode. 

    Hope this helps, please let me know for any further questions.

    Thanks,

    Sri