Tool/software:
Hi,
I have question about pre-emphasis function of SN75DPHY440SS.
Here is our configuration.
We measured input signal of DSI and output signal of DSI as differenatial signal.
We set "PRE_CFG1" as 2.5dB and "VSADJ_CFG0" as "Vim".
From datasheet description, I thought I can see VOD=200mV signal. However, as I showed above, output signal became VOD=300mV (approx 2dB).
When we changed "PRE_CFG1" as 0dB, Output signal level became same as input signal level (mean VOD=200mV).
Then I have following question.
Q1.I thought when I set "VSADJ_CFG0" to "Vim", internal pre-emphasis work as kind of adaptive emphasis (adjust to VOD=200mV or 220mV depending on input level.)
However, when I checked waveform, it seems that this function(pre-emphasis) work fixed emphasis (add certain level (in this case 2.5dB) to output independent to input level.)
Which understanding is correct ?
Q2. If later understanding is correct, I understand meaning of following sentence of datasheet.
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This feature must only be used when the HS pre-emphasis bit (transition bit) is attenuated by the channel. Enabling pre-emphasis in a system that has little channel loss (transition bit is not attenuated) may result in negative impact to system performance.
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However, in this case, I can not understand difference between VIL and VIM setting of "VSADJ_CFG0".
If later understandig of previous question is correct, could you please explain difference of VIL and VIH of "VSADJ_CFG0" ?
Best Regards,
