DS90UH940-Q1EVM: MIPI CSI Output clk is not differential

Amelie Zheng

Part Number: DS90UH940-Q1EVM

Hi Team,

My customer has ordered a 940 EVM to test and debug for new project. And found a very strange thing.

When they enable 940's internal Pattern Generation, the set up is following:

ADD	Register Name	Function	Bit	SET
0x64	PGCTL	PATGEN_SEL	7:4	0101
		PATGEN_UNH	3	0
		PATGEN_COLOR	2	1
		PATGEN_VCOM_REV	1	0
		PATGEN_EN	0	1

MODE_SEL0 is mode 4

MODE_SEL1 is mode 3

But when testing the MIPI CSI CLK signal, CLK+ and CLK- are as following:

And the CLK+ and CLK- waveforms are as following, nearly the same, not differential. But the D0-D4 are differential.

Could you please give some advice why the clk is not differential? Thanks!

over 5 years ago

0 Casey McCrea over 5 years ago

TI__Guru** 103215 points

Hello Amelie,

These waveforms are correct. CSI-2 clock and data lines transition back and forth between single ended and differential throughout each video line. You are too zoomed out on the scope to see the differential HS mode. Please see page 23 of the 940 datasheet for example pictures of CSI-2 P and N lanes zoomed in.

Best Regards,

Casey

0 Amelie Zheng over 5 years ago in reply to Casey McCrea

TI__Genius 10865 points

Hi Casey,

Thanks for your reply. Not sure whether I got your point, customer need to zoom ns not us to see differential siagnal.

0 Casey McCrea over 5 years ago in reply to Amelie Zheng

TI__Guru** 103215 points

Hello Amelie,

Yes, if you take CH1-CH2, then zoom in on the math waveform in the area shown by the red box, then you will see a differential signal with around 200mV swing. The area circled in the red box is the DPHY HS mode signaling which is differential between P/N.

Best Regards,

Casey

0 Amelie Zheng over 5 years ago in reply to Casey McCrea

TI__Genius 10865 points

thanks for so professional answer!

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DS90UH940-Q1EVM: MIPI CSI Output clk is not differential