SN75DP130 - Mechanism of self configuring Equalizer

Hello Kawai,

Thanks for your interest on the SN75DP130, we are reviewing your questions and will be answering them ASAP.

Regards,

Hello Moises-san,

Thank you for the information.

[Question 3]
I understood that the SN75DP130 automatic EQ gain setting depends on the pre-emphasis level setting based on link training. When pre-emphasis level is low --> EQ gain would be high, and when pre-emphasis level is high --> EQ gain would be low.

I have one question here. If the trace length between the Source CPU or FPGA and SN75DP130 is very short (e.g. very low loss), in the case when "(L0)" is selected, the signal would be over equalized and the signal would not be optimized. When do you use automatic EQ selection and what is the best way to optimize the EQ gain ?

Please also allow me to ask you one more question.

[Question 4]
Our customer will use the SN75DP130 on source side application. Link training would be used for the display port monitoring AUX signal, however, their Source side FPGA will always output the differential signal in the same swing level to SN75DP130 (No VOD/Pre-emphasis function on the FPGA side). In this case, I believe that SN75DP130 can operate correctly as long as the device input signal level is inside the electrical characteristics "MAIN LINK TERMINALS - VID".
Is my recognition correct ?

** However, jitter characteristic would be worse if EQ gain is not optimized.

Thanks in advance.

Best Regards,
Kawai

Hi Kawai-san,

[Question 3]

I need to contact design team to answer this question, please let me contact them and I'll be back with an appropriator answer.

[Question 4]

That's right, SN75DP130 can operate correctly as long as VID is complaint with MAIN LINK TERMINALS - VID. specification.

Hi Moises-san,

Thanks for your great support. I look forward to hearing from you soon.

Best Regards,
Kawai

Hello Moises-san,

Thanks for your reply.

I've understood that if auto EQ function is used, EQ level is set only based on the Link2 cable length and PE level under Link training. So in the case of very short Link1 trace length, user may need to adjust EQ level through I2C for optimization.

In the case of our customer, their DP source device does not have VOD control and PE function but have AUX communication signal. Their DP source device will communicate with DP sink device based on AUX and they will use the DP130 VOD/PE optimization for link training.
I think this does not have any problem as long as input signal level for DP130 is met.
Could you please advise us if there is any concern ?


Best Regards,
Kawai

Hi Kawai-san,

From design team response:

AEQ ensures not too much EQ  with large PE that can potentially degrade eye.

So, having DP130 should work fine being close to source device.

Regards

Hello Moises-san,

I apologize for my delay. Thanks for the feedback.

I have forgotten that, in general, using DP repeater means that there is some trace length (loss) between source device and DP connector (Link1). I agree in this case. EQ and PE were in inverse proportion because the relation should be, EQ gain + PE gain = Link1 loss.

In my customer case, their source device does not have PE function and only have fixed VOD. It does not have full link training function DP, however, it does have AUX signal to communicate with the sink device. Our customer wants to use DP130 to achieve link training with the sink device. If their were only small loss between source chip and DP130 (trace length 10-20mm), I believe AEQ could potentially over equalize and degrade the eye.

Best Regards,
Kawai

Hi Kawai-san,

Should be no problem, if this application has fixed VOD and no pre-emphasis (Pre-emphasis level 0 and pre-empahsis Post Cursos2 Level 0), AEQ has a maximum gain of 8 dB, AEQ will choose the optimum, which could be any value from 8 dB down to 0 dB.

Regards

Hellos Moises-san,

Isn't the EQ gain fixed to pre-emphasis(PEM) setting one by one like below ? Maybe I had been misunderstanding.

If PEM level is L0, EQ gain will be AEQ(L0) = 8dB
If PEM level is L1, EQ gain will be AEQ(L1) = 6dB
If PEM level is L2, EQ gain will be AEQ(L2) = 3.5dB
If PEM level is L3, EQ gain will be AEQ(L3) = 0dB

Does automatic EQ function scan all AEQ(L0) to AEQ(L3), then selects the best EQ gain setting ?

Best Regards,
Kawai

Hi Kawai-san,

From design team response, EQ gain is not fixed, it is a maximum value.
e.g.
If PE is L0, EQ gains could be up to 8dB, but if a lower value is needed it is used.
There is no scan over PE levels' gain.

Regards

Hi Moises-san,

Please let me summarize my recognition for automatic low-range EQ .

When PE is L0, the best EQ gain is chosen from 8, 6, 3.5, or 0dB.
When PE is L1, the best EQ gain is chosen from 6, 3.5, or 0dB.
When PE is L2, the best EQ gain is chosen from 3.5 or 0dB.
When PE is L3, EQ gain is always 0dB.

Am I understanding correctly ?

Best Regards,
Kawai

Hi Kawai-san,

This is sensitive information, what is the purpose of obtaining such data?
Could you please provide the customers information?

Regards

Hi Moises-san,

Is this a sensitive information ? We just would like to understand the simple operation of the automatic equalization to make clear that there would not be a problem in our customer application.

We had below answers from you which is conflicting. Answer1 mentioned that EQ gain is a fixed value based on PE level. However, your answer2 says EQ gain is optimized from the value in table3 (selection out of 4 levels).  Which is true ??

 [Your answer 1]
SN75DP130 will choose EQ gain according to pre-emphasis result from link training, as table 3 note (2) states.
"(L0)" / "(L1)" / "(L2)" / "(L3)" are pre-emphasis levels from link training

e.g.
After link training pre-emphasis level is L2, then EQ gain will be 10dB at 2.7GHz

[Your answer 2]
If this application has fixed VOD and no pre-emphasis (Pre-emphasis level 0 and pre-empahsis Post Cursos2 Level 0), AEQ has a maximum gain of 8 dB, AEQ will choose the optimum, which could be any value from 8 dB down to 0 dB.

 

Best Regards,
Kawai

Hello Moises-san,

I greatly appreciate for your continuous support. I have finally understood the operation for the automatic equalization. Regarding your comment, the device equalization level which is selected would follow below condition.

When PE is L0, the best EQ gain is selected from 8.0 / 6.0 / 3.5 / 0 dB.
When PE is L1, the best EQ gain is selected from 6.0 / 3.5 / 0 dB.
When PE is L2, the best EQ gain is selected from 3.5 / 0 dB.
When PE is L3, EQ gain is always 0 dB.

It seems it could be used with automatic equalization function. However, we are asking customer to fix the EQ level to 0dB or low gain as they only have 10-30mm trace between the source device and the DP130. We will ask customer for enough evaluation.

Best Regards,
Kawai