LMH1297: sdi_io_drv_pre_val

K.Yaita

Part Number: LMH1297

Hi Team,

Is there any information about sdi_io_drv_pre_val of ConfigIO Register 0x62 [6:5]?
I couldn't catch if pre-emphasis is increased or decreased when the value is incremented.
I would also like to know the gain value for our reference.

Best Regards,
Yaita

over 5 years ago

+1 Nasser Mohammadi over 5 years ago

TI__Guru* 93570 points

Hi Yaita-San,

Pre-emphasis is directly proportional. However, this has not been characterized.

Regards,, Nasser

0 K.Yaita over 5 years ago in reply to Nasser Mohammadi

Guru 29720 points

Hi Nasser-san,

Thank you always for your support.
If we change sdi_io_drv_pre_val "10 (default)" to "00", does pre-emphasis weaken?
I would like to know what case we should adjust the parameters.
Is it recommended to adjust the parameter to meet long cable?

Best Regards,
Yaita

+1 Nasser Mohammadi over 5 years ago in reply to K.Yaita

TI__Guru* 93570 points

Hi Yaita-San,

If you change this parameter to oo it weakens the pre-emphasis.

Also, please do not recommend to change this parameter to meet long cable reach. This parameter affects over/under shoot of the waveform. Changing this parameter may cause violation of the SMPTE +/-10% over/under shoot requirement.

Regards,, Nasser

0 K.Yaita over 5 years ago in reply to Nasser Mohammadi

Guru 29720 points

Hi Nasser-san,

Thank you for your answer.
Is it not recommended even weakens the pre-emphasis from default?
The background of the question is I heard my customer saw CRC error when sdi_io_drv_pre_val =10 (default) with CANARE L-5.5CUHD 70m cable.
He set sdi_io_drv_pre_val =00 then he saw no CRC error.

Best Regards,
Yaita

+1 Nasser Mohammadi over 5 years ago in reply to K.Yaita

TI__Guru* 93570 points

Hi Yaita-San,

With present settings we meet SMPTE requirements. Perhaps customer layout could be different. You can use LMH1297EVM to re-produce the error condition noted by the customer. This is the first time we hear pre-emphasis setting causing error under certain condition. Please note after 70m cable attenuation the high frequency content of the pre-emphasis is gone.

Regards,, Nasser

0 K.Yaita over 5 years ago in reply to Nasser Mohammadi

Guru 29720 points

Hi Nasser-san,

Thank you always for your support.
I would like to ask the following for my reference.

I believe the only requirement for SDI cable driver is to meet SMPTE specification.
On the other hand, how long can we extend cable length depends on SDI equalizer.
Is my understanding correct?

Best Regards,
Yaita

+1 Nasser Mohammadi over 5 years ago in reply to K.Yaita

TI__Guru* 93570 points

Hi Yaita-San,Your understanding is correct. The only requirement for SDI cable driver is meeting SMPTE output electrical parameter using a short cable -1m. There is nothing related to the cable reach. As you noted cable length is solely depends on the equalizer.

Regards,, Nasser

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LMH1297: sdi_io_drv_pre_val