Hdmi Inputs; Digital Outputs (Data And Clocks); Figure 137: Recommended Power Supply Decoupling - Analog Devices Advantiv ADV7604 Hardware Manual

ADV7604

Figure 137: Recommended Power Supply Decoupling

It is particularly important to maintain low noise and good stability of the PVDD (the clock
generator supply). Abrupt changes in the PVDD can result in similarly abrupt changes in sampling
clock phase and frequency. This can be avoided by careful attention to regulation, filtering, and
bypassing. It is highly desirable to provide separate regulated or heavily filtered supplies for each of
the analog circuitry groups (AVDD, CVDD, TVDD, and PVDD).
Some graphic controllers use substantially different levels of power when active (during active
picture time) and when idle (during horizontal and vertical synchronization periods). This can result
in a measurable change in the voltage supplied to the analog supply regulator, which can in turn
produce changes in the regulated analog supply voltage. This can be mitigated by regulating the
analog supply, or at least PVDD, from a different, cleaner, power source, for example, from a +12
V supply.
Repeatedly, experience has shown that the noise performance is the same or better with a single
ground plane. Using multiple ground planes can be detrimental because each separate ground plane
is smaller and long ground loops can result.
In some cases, using separate ground planes is unavoidable. For those cases, it is recommended to
place, at least, a single ground plane under the ADV7604. The location of the split should be under
the ADV7604. In this case, it is even more important to place components wisely because the
current loops are much longer (the current takes the path of least resistance).
Example of a current loop:
Power plane => ADV7604 => digital output trace => digital data receiver => digital ground plane
=> analog ground plane.

HDMI Inputs

The TMDS inputs of an unused HDMI port must be left unconnected.

Digital Outputs (Data and Clocks)

The trace length that the digital outputs have to drive should be minimized. Longer traces have
higher capacitance, which requires more current that can cause more internal digital noise. Shorter
traces reduce the possibility of reflections.
Adding a series resistor of value between 50 to 200 ohms can suppress reflections, reduce EMI, and
reduce the current spikes inside the ADV7604. If series resistors are used, they should be placed as
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Rev. F August 2010