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ONET1141L: Inductor/Ferrite Bead Spec and DC output drift

D.C.
Prodigy 210 points
Part Number: ONET1141L

Dear TI,

I have two questions.

1. What is the recommended  inductor or ferrite bead spec on page 22, Figure 21, used at the outputs OUT+ and OUT- pins? My circuit is very similar to the application circuit on page 22. Do these inductors/beads affect much on the instantaneous DC level of the outputs? I observed charging-up on low-output bit and discharging-down on high-output bit of the waveform at OUT+ for 10 Gbps and 1 Gbps. The impact of the 10Gbps is smaller as the bit period is shorter which leads to smaller discharging/charging. The changes of of the DC blocking capacitor value (1/10 and x10) does not change the outcome of the waveform. Any idea why this is happening?

2. In addition, this part is rated from 1Gbps to 10Gbps. Any tricks we can do on the register configuration or the supporting circuits to make the part run at lower data rates? Why this part is only rated down to 1 Gbps?

Thanks!

  • 0
    TI__Guru* 93670 points

    Greetings,

    The following bead was used used for evaluation of the ONET1141L: BMD15HD102SN1( www.murata.com/.../productdetail   ). This did not show droop in DC level. I am wondering if your bead may have a higher DC resistance or frequency response - assuming parasitic are minimized.  Please compare spec of this part versus the part you are using now.

    ONET1141L can operate at lower data rates however it has not been characterized and tested during manufacturing process.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 210 points

    Hi Nasser,

    Thanks for the Murata part number. Your bead does have higher impedance than mine. What is the recommended impedance required for the bead at the lowest operation frequency (longest running ones and zeros) of the chosen data rate? Do you have a SPICE model for the output behavior of OUT+ and OUT-?

    Thanks.

  • 0 in reply to D.C.
    TI__Guru* 93670 points

    Hi DC,

    I know this is the bead that was used for evaluation of the device. However, we did not use other beads with different low frequency impedances to characterize this behavior. I suppose this depends on the TOSA being used as well. Earlier, i noted there is not a spice model for this part.

    Regards,, Nasser