AD9883/PCB AD [Analog Devices], AD9883/PCB Datasheet - Page 23

• Manufacturer Part Number: AD9883/PCB
• Description: 110 MSPS Analog Interface for Flat Panel Displays
• Manufacturer: AD [Analog Devices]

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 regu-
lating the analog supply, or at least PV
power source (for example, from a 12 V supply).
It is also recommend to use a single ground plane for the entire
board. Experience has repeatedly shown that the noise perfor-
mance is the same or better with a single ground plane. Using
multiple ground planes can be detrimental because each sepa-
rate ground plane is smaller, and long ground loops can result.
In some cases, using separate ground planes is unavoidable. For
those cases, it is recommend to at least place a single ground
plane under the AD9883. 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
will be much longer, (current takes the path of least resistance).
An example of a current loop: power plane v AD9883 v digital
output trace v digital data receiver v digital ground plane v
analog ground plane.
PLL
Place the PLL loop filter components as close to the FILT pin
as possible.
Do not place any digital or other high frequency traces near
these components.
Use the values suggested in the data sheet with 10% tolerances
or less.
D
, from a different, cleaner,
Outputs (Both Data and Clocks)
Try to minimize the trace length that the digital outputs have to
drive. Longer traces have higher capacitance, which require
more current that causes more internal digital noise.
Shorter traces reduce the possibility of reflections.
Adding a series resistor of value 50 Ω–200 Ω can suppress
reflections, reduce EMI, and reduce the current spikes inside of
the AD9883. If series resistors are used, place them as close to
the AD9883 pins as possible, (although try not to add vias or extra
length to the output trace in order to get the resistors closer).
If possible, limit the capacitance that each of the digital outputs
drives to less than 10 pF. This can easily be accomplished by
keeping traces short and by connecting the outputs to only one
device. Loading the outputs with excessive capacitance will
increase the current transients inside of the AD9883 creating
more digital noise on its power supplies.
Digital Inputs
The digital inputs on the AD9883 were designed to work with
3.3 V signals, but are tolerant of 5.0 V signals. So, no extra
components need to be added if using 5.0 V logic.
Any noise that gets onto the Hsync input trace will add jitter to
the system. Therefore, minimize the trace length and do not run
any digital or other high frequency traces near it.
Voltage Reference
Bypass with a 0.1 µF capacitor. Place as close to the AD9883
pin as possible. Make the ground connection as short as possible.
AD9883