• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 540 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.

ONET1151L: Tuning the APC when handling pathological SDI Signals

SCOTT PELLET
Prodigy 10 points
Part Number: ONET1151L
Other Parts Discussed in Thread: LMH1218

Hi,

When running the IC in open loop mode, this IC can pass 11.88Gbps SDI video, as well as 3G-SDI with pathological stress-test pattern very well. However, in closed loop, the signal will nearly drop out.The datasheet has a recommended COMP cap value of 0.01uF to control the bandwidth of the APC loop. It seems the APC loop reacts too quickly when the large change in data density happens creating the pathological test pattern.

How large of a COMP cap value can be used? What does the APC circuit look like?

  • 0
    TI__Guru* 93670 points

    Hi Scott,

    Checked internal documents. APC loop time constant has not been characterized across different settings. Also, there hasn't been any validation using SDI pathological pattern. Perhaps you can change comp cap and observe if laser power is maintained however there hasn't been any validation under this environment.

    Regards,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 10 points

    Hi Nasser.

    I have a 10uF now, and that has helped some. I believe the bias pin will also need some 'extra' bypassing to slow down the changes in bias current. Flying blind a little :-) I'm surprised SDI hasn't been considered as there's some market for 12G-SDI SFP modules.

    Thank you for looking into this.

  • 0 in reply to SCOTT PELLET
    TI__Guru* 93670 points

    Hi Scott,

    This part was developed mainly targeting Ethernet applications. We do have SDI 75-ohm coax equalizer, driver, and CDRs however these are not going to address 12G SDI SFP module need. Another parameter that came to my mind, this part is rated at 11.33Gbps while 12G SDI requires 11.88Gbps.

    Regards,Nasser 

  • 0 in reply to Nasser Mohammadi
    Prodigy 10 points

    Yes, I am using your LMH1218 with this laser driver and it also works great. With the laser driver's ability to do 25 to 35ps rise/fall times, it's been fine at 11.88Gbps (open loop). Crosspoint and EQ are disabled and don't seem to affect signal integrity. It's just the APC mode. Will test this week with various COMP caps.

    thanks!