AM3352: LCD pixel clock question

Mark Pearson

Part Number: AM3352

AM3352 pixel clock question.pptxAttached is a picture (06) of a measurement of the pixel clk coming from the AM3352 on a design I am working on. It is a very sinusoidal signal. I would have expected it to be a square wave. I do have a 33 ohm resistor in series, but I shorted it out in the 07 image. All that did was make it more sinusoidal. I am also concerned that the signal isn’t reaching either 0V or 3.3V.

Do either of you have any thoughts on this topic? Is there any sort of drive strength control on this chip?

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

Hi,

Please describe the measuring equipment - probe, bandwidth, etc.

0 Mark Pearson over 7 years ago in reply to Biser Gatchev-XID

TI__Genius 12705 points

5241.AM3352 pixel clock question.pptxMore feedback & details:

Good question, the new scope shots are on a 300MHz scope full bandwidth. I was using a 100MHz scope not on full bandwidth. The 100MHz scope still can’t get a good read on the signal at full bandwidth though.

Picture 08 has the 33 ohm and 09 is without the 33 ohm. 10 is without the LCD attached and no 33ohm. In 12 I bypassed the PCLK trace with 30 AWG wire, so I don’t think it is the stack up. Single ended 10x passive probe (tek P6139B), DC coupling

Updated PPTX file attached.

0 Biser Gatchev-XID over 7 years ago in reply to Mark Pearson

TI__Guru**** 393215 points

Where are you probing? Near the processor pin or at the far end? Is there a chance that there are any capacitors tied to this line?

0 Mark Pearson over 7 years ago in reply to Biser Gatchev-XID

TI__Genius 12705 points

The measurement is at the LCD end (load). No additional capacitors - only parasitic capacitances from the cabling.
I am not worried about the display working since this is the configuration we are using on other designs. I am more worried about harmonics causing me to fail emissions testing.
I think the poor waveform is due to the passive, DC coupled probe with a long GND lead.

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AM3352: LCD pixel clock question