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ONET8501PB: Odd behavior in pre emphasis settings

Caleb Taber
Prodigy 20 points
Part Number: ONET8501PB

Hello experts,

I have found an odd issue while using the ONET8501PB as the RX for an O/E application. During programming I set the pre emphasis settings on register 2 to a value of 8 (1000), which is not listed as a possible value in the data sheet, and got the following result:

Similar results can be seen when writing for 2 (0010) and A  (1010) which are also not listed in the data sheet as possible values. Using a value form the data sheet, in this example C, gives the following result wherein the output power is reduced considerably:

The output from the ONET8501PB when using an unlisted value is more useful for my application but I am worried about possible repercussions as this is not a listed value in the data sheet. Does anyone know why I am getting this output or if there are any design problems that may arise from using unlisted values. This is an urgent issue and has formed a bottleneck in trying to decide if this a valid solution or not so any help would be appreciated. 

  • 0
    TI__Guru* 93670 points

    Hi Caleb,

    These settings that you have used are in-between or finer settings. The recommendation in the data sheet refers to the different dB preemphasis settings. The only recommendation is to check 4-5 parts just to make sure it meets your application and you get consistent result. Device has not been evaluated at settings you noted.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    This is good to know but why does it give such a boost in output power at multiple points if it in between? I get the same result if I write at several points that are not listed in the data sheet despite those points being several dB apart.