LMH0397: Termination resistor

mehmet ergani

Part Number: LMH0397

Hi All,

We design carrier board for a AMD (Xilinx) ultrascale+ SOM board. This carrier board grabs 3G-SDI data and transmits to GTH banks. We use LMH0397 3G-SDI Bidirectional I/O IC as SDI cable EQ and UHD-SDI GT IP in digital design.

As shown in picture (taken from PG380 UHD-SDI GT product Guide) GTH banks have 100ohm termination resistor. LMH0397 has on-chip 100ohm termination resistor too.

Do having termination resistor on both sides (receiver and transmitter) affect quality of video? Should we disable on-chip resistor of LMH0397?

Thanks.

over 1 year ago

+1 Nasser Mohammadi over 1 year ago

TI__Guru* 93670 points

Hi Mehmet,

Having termination on both sides should not be an issue - actually this is recommended. Please note data sheet diagram shown below. FPGA receiver is expected to have 100-ohm termination.

Regards, Nasser

0 mehmet ergani over 1 year ago in reply to Nasser Mohammadi

Prodigy 10 points

Hi Nasser again,

While the TI cable equalizer is 100ohm terminated and therefore suggests 100 ohm routing, the Xilinx SOM suggests using 90ohm impedance even though it’s internally terminated through 2x 50ohm resistors, to avoid reflection at the SOM connectors. What is the better routing option in this case? 90, 95, 100 ohm?

thanks

LMH

GTH

0 Nasser Mohammadi over 1 year ago in reply to mehmet ergani

TI__Guru* 93670 points

Greetings,

Please use 90-ohm instead to provide a better impedance match with the SOM connector.

Regards, Nasser

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LMH0397: Termination resistor