ONET8501PB: ONET8501PB input threshold adjustment range

Dmitri Snejko

Part Number: ONET8501PB
Other Parts Discussed in Thread: ONET1151P, ONET8501P

Hi,

ONET8501PB and ONET1151P are offering some input threshold adjustments. But it is in digital form from 1 to 255 and there is no specification what exact range is covered with the DAC. How is it exactly working? Is this setting relative to the average power? And what is the range between min and max settings. Is it possible to re-scale it?

Regards, Dmitri Snejko

over 6 years ago

0 Nasser Mohammadi over 6 years ago

TI__Guru* 93670 points

Hi Dmitri,
Please note figure 9 & 10 of the data sheet where we show register settings vs LOS
assert/de-assert and LOSRANG bit settings.

Regards,,nasser

0 Dmitri Snejko over 6 years ago in reply to Nasser Mohammadi

Intellectual 745 points

Hi Nasser,
Thanks for the reference but I was asking about the input threshold setting (reg 0x01). It is responsible for decision making and has quite strong influence for performance. I cant find any quantization for this parameter. How stable it is and how variate the parameter with temperature or between parts
Regards, Dmitri.

0 Nasser Mohammadi over 6 years ago in reply to Dmitri Snejko

TI__Guru* 93670 points

Hi Dmitri,
Register noted in figure 9 and 10 corresponds to reg 0x01 settings.
I checked earlier data collected and was not able to see additional data regarding reg 0x01 settings vs LOS assert/de-assert.
Regards,,nasser

0 Dmitri Snejko over 6 years ago in reply to Nasser Mohammadi

Intellectual 745 points

Hi Nasser,

I am not sure you are right.

Figure 9. LOS Assert/Deassert Voltage vs Register Setting LOSRNG = 0

Figure 10. LOS Assert/Deassert Voltage vs Register Setting LOSRNG = 1

LOS threshold is controlled by regs 8,9,10 or 11, which are selected by RATE pins. While reg 1 is controlling the decision threshold. Which has to be related to average input power. We see an effect of this register setting on BER performance but the datasheet has practically no information.

Regards, Dmitri

0 Nasser Mohammadi over 6 years ago in reply to Dmitri Snejko

TI__Guru* 93670 points

Hi Dmitri,

I looked into this deeper and indeed this register 0x01 sets slicer level or where we detect 0 or 1 on the input side. It is not related to the LOS threshold level settings as you noted.

Also, I have been searching in ONET8501P or ONET1151P. These two devices use the same THADJ register as well - ONET1151P has CPRNG bits as well.

However, I was not able to find THADJ step versus crossing or duty cycle distortion. I am thinking perhaps you can disable offset correction and use a fixed slew rate signal. Then change this register content. Given this, you would be able to determine DCD versus reg 0x01 setting. Also, you can add +/-30% due to part to part variation.

Regards,,nasser

0 Dmitri Snejko over 6 years ago in reply to Nasser Mohammadi

Intellectual 745 points

Thanks Nasser,

Do you think someone from the development team can give more information?

Regards, Dmitri

0 Nasser Mohammadi over 6 years ago in reply to Dmitri Snejko

TI__Guru* 93670 points

Hi Dmitri,
With one of the designers, we actually looked at the evaluation report. Unfortunately, we did not see a report describing this.
Regards,,nasser

0 Dmitri Snejko over 6 years ago in reply to Nasser Mohammadi

Intellectual 745 points

Hi Nasser

Ok. We will try to measure it on our dev board.

Thanks, Dmitri

0 Nasser Mohammadi over 6 years ago in reply to Dmitri Snejko

TI__Guru* 93670 points

Thanks Dmitri,

Regards,,nasser

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ONET8501PB: ONET8501PB input threshold adjustment range