ADV8005 TTL Output Jitter

I'm using the TTL outputs on the ADV8005 to drive an SDI transmitter at 1080p and I'm seeing a lot of jitter on the PCLK output.  I've been using my computer background as a test image and I've been measuring almost 3ns of jitter using this background.  Interestingly, if I use an all white test image, or even better let the HDMI receiver free run, the jitter decreases significantly to around 500ps.  In both cases, the test image is also routed to the DVI and is stable with no issues.

I've checked my 1.8V power supply for switching noise and it doesn't appear to be the culprit to me.  I've attached a document with screenshots of both the PCLK jitter and the 1.8V ripple and switching noise.

Besides the 1.8V power supply, what could cause sever jitter on the TTL outputs while leaving the DVI output acceptable?

Thanks.

PCLK_Jitter.docx
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  • Hi Anthony,

    The power supplies should be more than sufficient for powering the board, the 1.8V is ADP2165 and is rated for 5A and the 3.3V is LTM4625 also rated for 5A.  Total combined current draw from the board with everything running is approximately 1.5 Amps, so there should be plenty of headroom in the supplies.

    The droop was caused by a current sense resistor in-line with the 1.8V supply.  Once that was removed the power was in spec at all times.  Both 3.3V and 1.8V have their own separate power plane layer which supplies power to all of the chips.  The ADV8005 draws directly from the power planes and then has individual filtering following the design of the EVAL board.

    I have the ADV8005 eval board, is there any way to use the TTL out on that board in a manner that will let me probe the PCLK?

    -Kevin

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  • Hi Anthony,

    The power supplies should be more than sufficient for powering the board, the 1.8V is ADP2165 and is rated for 5A and the 3.3V is LTM4625 also rated for 5A.  Total combined current draw from the board with everything running is approximately 1.5 Amps, so there should be plenty of headroom in the supplies.

    The droop was caused by a current sense resistor in-line with the 1.8V supply.  Once that was removed the power was in spec at all times.  Both 3.3V and 1.8V have their own separate power plane layer which supplies power to all of the chips.  The ADV8005 draws directly from the power planes and then has individual filtering following the design of the EVAL board.

    I have the ADV8005 eval board, is there any way to use the TTL out on that board in a manner that will let me probe the PCLK?

    -Kevin

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