DS90UH948-Q1: LCD display flickering issue when connecting to the DSI MIPI serializer DS90UB941AS-Q1

SIVAKUMAR KARAYIL ARAVINDAKSHAN

Part Number: DS90UH948-Q1
Other Parts Discussed in Thread: DS90UB941AS-Q1

We are analyzing a display flickering issue, observed with the DS90UH948-Q1 de-serializer when we are connecting it to the LVDS LCD display.

Our configuration is SD845 Processor MIPI DSI serial link => DS90UB941AS-Q1 serializer => Single ended FPD link cable => DS90UH948-Q1 de-serializer => 4 Lane LVDS LCD display - 60fps @ 71.9Mhz Pclk.

We have tried using the MIPI DSI clock reference for the DS90UB941AS-Q1 serializer, (MIPI clock with external timing ;Register 0x56 to 0x00 and 0x65 to 0x00)

o The display is stable but when we operate the touch screen display is flickering

o Probed the LOCK signal of de-serializer during the touch event, and the LOCK signal is going LOW on touch.

What could be the reason for the PLL losing the synch (LOCK signal toggling) during the touch event? Could you please provide your expert advise on this?

We have also tried using a 72Mhz external clock as reference for the DS90UB941AS-Q1 serializer. The setting used is external clock with external timing; Register 0x56 to 0x01 and 0x65 to 0x00 )

o The display is flickering continuously

o Probed the LOCK signal of the de-serializer, and this signal is always HIGH.

over 4 years ago

0 Charley Cai over 4 years ago

TI__Genius 12866 points

Hi Sivakumar,

Could you provide a register dump of the 941AS and 948 devices?

For the external clock case, if you start a touch event, does the lock drop?

Could you share some info on the display timing just to ensure the flicking is not due to timing mismatch?

Best Regards,

Charley Cai

0 SIVAKUMAR KARAYIL ARAVINDAKSHAN over 4 years ago in reply to Charley Cai

Prodigy 65 points

Hi Charley Cai,

Please find the document attached here for the I2C register dump data of the serializer (941AS) and the de-serializer(948) with external 72Mhz clock reference to the serializer and DSI internal clock reference.

The document also contains the scope capture of the LOCK signal status of the de-serializer in above cases.

Regards,

Sivaser_des_i2cdump.pdf

0 SIVAKUMAR KARAYIL ARAVINDAKSHAN over 4 years ago in reply to Charley Cai

Prodigy 65 points

Hi Charley Cai,

The document also contains the scope capture of the LOCK signal status of the de-serializer in above cases.

Regards,

Siva1016.ser_des_i2cdump.pdf

0 Charley Cai over 4 years ago in reply to SIVAKUMAR KARAYIL ARAVINDAKSHAN

TI__Genius 12866 points

Hi Siva,

Could we zoom in on the lock drop event and look at the time period where the lock is low?

If the lock drop like shown in the PDF, the display should have flickered.

Touch event should have not affected the display from my understanding. I will look into the reg dump and get back to you within two days.

Best Regards,

Charley Cai

0 Charley Cai over 4 years ago in reply to Charley Cai

TI__Genius 12866 points

Hi Siva,

Could you help probing the touch control I2C traffic at the I2C Master and I2C slave side?

Would you be able to provide an example of the touch control I2C transactions?

Could you also help providing the schematic for the devices?

Best Regards,

Charley Cai

0 SIVAKUMAR KARAYIL ARAVINDAKSHAN over 4 years ago in reply to Charley Cai

Prodigy 65 points

Hi Charley Cai,

Please find the attached pdf document for the I2C waveform capture on the serializer side and de-serializer side. Could you please share your mail id, so that I can share the schematic with you in mail.

Warm Regards,

Siva

i2CWaveform capture for the touch event.pdf

0 Charley Cai over 4 years ago in reply to SIVAKUMAR KARAYIL ARAVINDAKSHAN

TI__Genius 12866 points

Hi Siva,

I have sent you my email over private message.

Best Regards,

Charley Cai

0 SIVAKUMAR KARAYIL ARAVINDAKSHAN over 4 years ago in reply to Charley Cai

Prodigy 65 points

Hi Charley Cai,

Please find the attached pdf document for the I2C register dump comparison with LOCK signal = HIGH state , and LOCK signal = LOW state for both the serialiser and de-serialiser.

From this it looks like we are loosing the DSI input data. May be it is going out of lower threshold clock frequency range of the serialiser input range). Could you please check this and let us know your comments on this?

Warm Regards,

SivaSerializer_Deserializer_register_dump_report_V0.1.pdf

0 Charley Cai over 4 years ago in reply to SIVAKUMAR KARAYIL ARAVINDAKSHAN

TI__Genius 12866 points

Hi Siva,

Do you have the capability to monitor DSI clock with scope?

It is strange that touch control affects the DSI clock.

Best Regards,

Charley Cai

0 SIVAKUMAR KARAYIL ARAVINDAKSHAN over 4 years ago in reply to Charley Cai

Prodigy 65 points

Hi Charley Cai,

No. We don't have a scope capable of capturing the DSI input clock jitter. Did you get a chance to look in to the register changes we have captured during the issue (lock signal low).

Could you please provide your feedback on this ?

Regards,
Siva

0 Charley Cai over 4 years ago in reply to SIVAKUMAR KARAYIL ARAVINDAKSHAN

TI__Genius 12866 points

Hi Siva,

Yes, from the register read, it looks like the DSI clock is not supplied when the lock dropped.

You could follow this guide to debug DSI related issues.

Best Regards,

Charley Cai

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DS90UH948-Q1: LCD display flickering issue when connecting to the DSI MIPI serializer DS90UB941AS-Q1