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Concern on EMI issues if the pin-2 (TMDS DATA2 SHIELD) of HDMI/MHL (Dual Mode) connector used for CD_SENSE (Cable Detection for MHL)

Question asked by padmanathanj on Jan 20, 2014
Latest reply on Jan 20, 2014 by padmanathanj

Hi,

 

     In our design, we are using a Dual-Mode MHL/HDMI Receiver (ADV7XXX proprietary part from ADI).

As it is recommended to use the Pin-2 (TMDS DATA2 SHIELD) of the HDMI connecter as CD_SENSE, please confirm if it can cause any EMI issues.

 

Since TMDS is not a truly differential signal; in HDMI Mode, the expected Return path for TMDS DATA2 + and TMDS DATA2- are through the TMDS DATA2 SHIELD pin (which is used as a immediate shield in the HDMI cables for DATA2+ and - pair only).

However, since this DATA2 Shield pin is used as a signal CD_SENSE (for cable detection of MHL in Dual mode connectors) and not connected directly to the GND, the Return path for DATA2/- will be closed through the other DATAx Shield connection between HDMI Source and Sink.

Is there any EMI issues to be expected due to this long Return path in the products designed with  Dual mode Input ports (single connector for both HDMI/MHL)?.

 

To avoid this, is there any AC (Capacitive) path included internal to the receiver device or required externally to provide the proper return path for the DATA2+/-.

 

Thanks & Regards,

Padmanathan J

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