Noise in the DVI Output of ADV7511W

Hi,

Thanks for your feedback.

We took out the card from the system and made a test jig as shown in the attached figure.

We had probed and captured the POWER, INPUT DATA LINES, INPUT CLOCK and OUTPUT lines of ADV7511 in Card 14. Everything looks very clean and fine.

Later when we Touch the DVI OUT Data line Tx1+ and Tx1- only on corresponding  pins of connector P2 in card 14 through finger , we observed that all the noise on DVI display were cleared. We observe not a single dot on the display when we touch the Tx1+ and Tx1- pins of DVI OUT interface on P2 connector, if we remove the finger the dots re appear on the screen. Same observation was found if we touch the wires of Tx1+ and Tx1- in the DVI Cable set connected to Rare side of P2 connector in the backplane.

We assumed that the Tx1+ and 1- is picking up the noise at the P2 connector side of card 14, we tried connecting a common mode choke (90 OHM) in series with the Tx1+ and Tx1- (by cutting the traces on backplane card). But no improvement was found.

In card 14, there is an RS422 differential pair routed in between the pins for Tx1+ and Tx1- of P2 . Assuming that these lines causing noise over the DVI signals, we disabled the RS422 IC. We observed improvement in the noise level (the number of dots were reduced).

Finally, we covered the DVI Cables (that is connected to Rare side of P2 as shown in figure) with Copper tapes. All the noisy dots disappeared from the DVI display. This is how the issue is currently solved. We are not sure whether we will be able to reduce the noise in the system by the same procedure (by shielding the cables properly with copper tapes). We will get back to you very soon with the result after checking in the final system.

Regards,

Vijetha

Hi,

Thanks for your feedback.

We took out the card from the system and made a test jig as shown in the attached figure.

We had probed and captured the POWER, INPUT DATA LINES, INPUT CLOCK and OUTPUT lines of ADV7511 in Card 14. Everything looks very clean and fine.

Later when we Touch the DVI OUT Data line Tx1+ and Tx1- only on corresponding  pins of connector P2 in card 14 through finger , we observed that all the noise on DVI display were cleared. We observe not a single dot on the display when we touch the Tx1+ and Tx1- pins of DVI OUT interface on P2 connector, if we remove the finger the dots re appear on the screen. Same observation was found if we touch the wires of Tx1+ and Tx1- in the DVI Cable set connected to Rare side of P2 connector in the backplane.

We assumed that the Tx1+ and 1- is picking up the noise at the P2 connector side of card 14, we tried connecting a common mode choke (90 OHM) in series with the Tx1+ and Tx1- (by cutting the traces on backplane card). But no improvement was found.

In card 14, there is an RS422 differential pair routed in between the pins for Tx1+ and Tx1- of P2 . Assuming that these lines causing noise over the DVI signals, we disabled the RS422 IC. We observed improvement in the noise level (the number of dots were reduced).

Finally, we covered the DVI Cables (that is connected to Rare side of P2 as shown in figure) with Copper tapes. All the noisy dots disappeared from the DVI display. This is how the issue is currently solved. We are not sure whether we will be able to reduce the noise in the system by the same procedure (by shielding the cables properly with copper tapes). We will get back to you very soon with the result after checking in the final system.

Regards,

Vijetha