LMH1228: 12G SDI return loss test

Takashi Yamaguchi

Genius 13500 points

Part Number: LMH1228
Other Parts Discussed in Thread: LMH1297

Hi team,

My customer is going to test the 12G SDI return loss. Could you please advise me on the following?

<Premise>
It is a system that outputs single end from SDO_OUT1.

When the LMH1228 is powered on, is SDO_OUT1 adjusted to 75Ω? (Is it possible to measure the return loss just by turning on the power, is there no need to set registers?)

Regards,

Yamaguchi

over 4 years ago

+1 Nasser Mohammadi over 4 years ago

TI__Guru* 93670 points

Greetings Yamaguchi,

Return loss is measured when the device is powered on. Additionally we should turn on 10MHz output clock to keep alive the AC coupling Cap. LMH1228/LMH1297 GUI allows or it can be used to turn on the 10MHz clock. Also, please note LMH1228 programming guide as well - this shows step by step settings for enabling 10MHz output clock.

Regards ,,Nasser

0 Takashi Yamaguchi over 4 years ago in reply to Nasser Mohammadi

TI__Genius 13500 points

Hi Nasser-san,

Thank you for the answer. My customer understood it. I received additional questions from the customer.

It was stated that the 10MHz clock is output from the OUT0 pin. This time, the customer doesn't use the OUT0 pin. In that case, is the 10MHz clock output still necessary?

Where will the 10MHz clock output be used to maintain the AC coupling cap?
(Is it between LMH1228 and host device?)

Regards,

Yamaguchi

+1 Nasser Mohammadi over 4 years ago in reply to Takashi Yamaguchi

TI__Guru* 93670 points

Greetings Yamaguchi-San,

10MHz clock will go out on 75-ohm coax on SDI_OUT1 and SDI_OUT2. This is used to keep alive the AC coupling Cap between 75-ohm coax cable and SDI output of the LMH1228 device.

Regards ,, Nasser

0 Takashi Yamaguchi over 4 years ago in reply to Nasser Mohammadi

TI__Genius 13500 points

Hi Nasser-san,

Thank you for the answer. My customer understood.

Regards,

Yamaguchi

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LMH1228: 12G SDI return loss test