AD9889 Analog Devices, AD9889 Datasheet - Page 42

• Manufacturer Part Number: AD9889
• Description: High Performance HDMI/DVI Transmitter
• Manufacturer: Analog Devices

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DataSheet
AD9889
PCB LAYOUT RECOMMENDATIONS
The AD9889 is a high precision, high speed analog device. As
such, to get the maximum performance out of the part, it is
important to have a well laid out board. The following is a guide
for designing a board using the AD9889.
POWER SUPPLY BYPASSING
It is recommended to bypass each power supply pin with a
0.1 μF capacitor. The exception is when two or more supply
pins are adjacent to each other. For these groupings of
powers/grounds, it is necessary to have only one bypass
capacitor. The fundamental idea is to have a bypass capacitor
within about 0.5 cm of each power pin. Also, avoid placing the
capacitor on the opposite side of the PC board from the
AD9889, as that interposes resistive vias in the path.
The bypass capacitors should be physically located between the
power plane and the power pin. Current should flow from the
power plane to the capacitor to the power pin. Do not make the
power connection between the capacitor and the power pin.
Placing a via underneath the capacitor pads, down to the power
plane, is generally the best approach.
It is particularly important to maintain low noise and good
stability of PV
PV
phase and frequency. This can be avoided by careful attention to
regulation, filtering, and bypassing. It is highly desirable to
provide separate regulated supplies for each of the analog
circuitry groups (V
Some graphic controllers use substantially different levels of
power when active (during active picture time) and when idle
(during horizontal and vertical sync 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 PV
cleaner power source (for example, from a 12 V supply).
D
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can result in similarly abrupt changes in sampling clock
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D
(the clock generator supply). Abrupt changes in
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Rev. 0 | Page 42 of 48
It is also recommended to use a single ground plane for the
entire board. Experience has shown repeatedly that 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, so it
is recommended to place a single ground plane under the
AD9889. The location of the split should be at the receiver of
the digital outputs. For this case, it is even more important to
place components wisely because the current loops are much
longer (current takes the path of least resistance). Figure 13
shows an example of a current loop.
DIGITAL INPUTS
The digital inputs on the AD9889 were designed to work with
1.8 V signals but are tolerant of 3.3 V signals. Therefore, no
extra components need to be added if using 3.3 V logic.
Any noise that gets onto the HSYNC input trace adds jitter to
the system. Therefore, minimize the trace length and do not run
any digital or other high frequency traces near it.
Figure 13. Current Loop
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