AD9983A/PCBZ Analog Devices Inc, AD9983A/PCBZ Datasheet - Page 39

• Manufacturer Part Number: AD9983A/PCBZ
• Description: Pb-free EVALUATION Kit AD9983A
• Manufacturer: Analog Devices Inc
• Series: Advantiv®r

Specifications of AD9983A/PCBZ

• Main Purpose: Video, Video Processing
• Embedded: No
• Utilized Ic / Part: AD9983A
• Primary Attributes: 3 x 8-Bit 140 MSPS ADC's
• Secondary Attributes: Integrated PLL & VCO
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PCB LAYOUT RECOMMENDATIONS
The AD9983A is a high precision, high speed analog device.
To achieve the maximum performance from the part, it is
important to have a well laid-out board. The Analog Interface
Inputs section provides a guide for designing a board using
the AD9983A.
ANALOG INTERFACE INPUTS
Using the following layout techniques on the graphics inputs is
extremely important:
•
•
•
•
•
Power Supply Bypassing
It is recommended to bypass each power supply pin with a
0.1 μF capacitor. The exception is where two or more supply
pins are adjacent to each other. For these groupings of
powers/grounds, it is only necessary to have 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
AD9983A, since that interposes resistive vias in the path.
Minimize the trace length running into the graphics
inputs. This is accomplished by placing the AD9983A as
close as possible to the graphics VGA connector. Long
input trace lengths are undesirable because they pick up
noise from the board and other external sources.
Place the 75 Ω termination resistors (see Figure 3) as close
as possible to the AD9983A chip. Any additional trace
length between the termination resistors and the input of
the AD9983A increases the magnitude of reflections,
which corrupts the graphics signal.
Use 75 Ω matched impedance traces. Trace impedances
other than 75 Ω also increase the chance of reflections.
The AD9983A has a very high input bandwidth, (200 MHz).
While this is desirable for acquiring a high resolution PC
graphics signal with fast edges, it also means that it captures
any high frequency noise present. Therefore, it is important
to reduce the amount of noise coupled to the inputs. Avoid
running any digital traces near the analog inputs.
Due to the high bandwidth of the AD9983A, sometimes
low-pass filtering the analog inputs can help to reduce
noise. (For many applications, filtering is unnecessary.)
Experiments have shown that placing a ferrite bead in
series prior to the 75 Ω termination resistor is helpful in
filtering excess noise. Specifically, the Fair-Rite
#2508051217Z0 was used, but an application could work
best with a different bead value. Alternatively, placing a
100 Ω to 120 Ω resistor between the 75 Ω termination
resistor and the input coupling capacitor is beneficial.
Rev. 0 | Page 39 of 44
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 the PV
changes in PV
sampling clock phase and frequency. This can be avoided with
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).
It is also recommended to use a single ground plane for the
entire board. Experience has repeatedly 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 at least place a single ground
plane under the AD9983A. The location of the split should be at
the receiver of the digital outputs. In 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 is power plane to
AD9983A to digital output trace to digital data receiver to
digital ground plane to 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
can result in similarly abrupt changes in
D
(the clock generator supply). Abrupt
D
and PV
D
D
).
, from a different,
AD9983A