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[SOLVED] Big EMI issue on LCD screen

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flote21

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Hello guys,

I have designed a display board to interface LVDS signal coming from a camera to parallel RGB interface LCD screen input.

The displayboard does not have any EMI problem. However when i connect it to the LCD screen thought a flat cable, a big EMI interference is coming out of the flat cable. The frequency of this EMI is at 25MHz and it has harmonics every 25MHz up to 700MHz. The 25 MHz is the pixel clock of the RGB data

I tried to reduce the EMI changing the values of the series termination resistors, i added more bypass capacitors, i place finger contacts to have more direct gnd contacts between the LCD screen and the display board....and i got some improvements but still the EMI levels are high.

Any idea to improve the current EMI results?

Thanks in advance.

Greetings
 

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No. The point is you add some jitter to the clock, but not enough to affect the relative timing between the clock edges and the data. You don’t need to demodulate anything.
 

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You don't nee "to recover the original DCLK" signal. The LCD must be able read the data with varying DCLK. RGB data and sync signals must be generated in phase with DCLK. You have a FIFO where the data is written with LVDS interface clock and read out with spread spectrum clock.

I don't know if the LCD may have problems if the interface is operated with spread spectrum clock. If you consider this option, you need to evaluate it.
 

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Hello everybody!!! Finally i got to reduce the EMI levels. The best solution was to place finger contacts like the following ones alon the bottom layer of the PCB. Those finger contacts are touching the metal housing of the TFT screen and I was able to reduce a lot the EMI issues.



Thanks for your advices.

Greetings
 

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Hi,

this is why I asked for metal frame, shielding, mechanical construction in post#7.
Never got a photo or a clear answer.

Klaus
 

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