LMH0387 EYE issue

Prescott Siao

Intellectual 2220 points

Other Parts Discussed in Thread: LMH0387

Hi team,

We did the test on the LMH0387 EVM.

Please refer the picture.

Could you please provide some comments on why the crossing is not in the middle?

Thanks.

Prescott

over 9 years ago

0 Nasser Mohammadi over 9 years ago

TI__Guru* 93670 points

Hi Prescott,

I was expecting 50% duty cycle vs what you are showing in this eye diagram. As you noted crossing should be in the middle.

Do you see this issue on all devices or just one part? How about if you use a video analyzer? Is the eye diagram not centered? Can you please send us customer schematic as well.

Below i have enclosed a copy of LMH0387EVM eye diagram at 270MBps(close to your measurements). As you can see the eye crossing is well centered.

Regards,,nasser

0 Prescott Siao over 9 years ago in reply to Nasser Mohammadi

TI__Intellectual 2220 points

Hi Nasser,

Thanks for your help.

Attached filed is customer's schematic.

If there is any comment, please let me know.

Thanks.

LMH0387_2.pdf

Prescott

0 Nasser Mohammadi over 9 years ago in reply to Prescott Siao

TI__Guru* 93670 points

Hi Prescott,

I checked the schematic:

Pin 36 we use 750 Ohm but in this schematic 716 ohm Resistor is used. Can customer change this to 750 ohm to see if crossing improves?

Also, do we see this issue on every board or some boards?

Regards,,nasser

0 Prescott Siao over 9 years ago in reply to Nasser Mohammadi

TI__Intellectual 2220 points

Hi Nasser,

The root cause is FPGA. Not our device. Many thanks.

Regards,
Prescott

0 Nasser Mohammadi over 9 years ago in reply to Prescott Siao

TI__Guru* 93670 points

Hi Prescott,

Thanks very much for the update.

Regards,,nasser

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LMH0387 EYE issue