AD9887KS-140 Analog Devices Inc, AD9887KS-140 Datasheet - Page 38

• Manufacturer Part Number: AD9887KS-140
• Description: IC INTRFACE ANALOG/DVI 160-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD9887KS-140

• Rohs Status: RoHS non-compliant
• Applications: Graphic Cards, VGA Interfaces
• Interface: Analog and Digital
• Voltage - Supply: 3.15 V ~ 3.45 V
• Package / Case: 160-MQFP, 160-PQFP
• Mounting Type: Surface Mount

AD9887
PCB LAYOUT RECOMMENDATIONS
The AD9887 is a high-performance, 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 AD9887.
Analog Interface Inputs
Using the following layout techniques on the graphics inputs is
extremely important:
Minimize the trace length running into the graphics inputs. This
is accomplished by placing the AD9887 as close as possible to
the graphics VGA connector. Long input trace lengths are unde-
sirable because they will pick up more noise from the board and
other external sources.
Place the 75 Ω termination resistors as close to the AD9887
chip as possible. Any additional trace length between the termi-
nation resistors and the input of the AD9887 increases the
magnitude of reflections, which will corrupt the graphics signal.
Use 75 Ω matched impedance traces. Trace impedances other
than 75 Ω will also increase the chance of reflections.
The AD9887 has very high input bandwidth, (330 MHz). While
this is desirable for acquiring a high resolution PC graphics
signal with fast edges, it means that it will also capture any high
frequency noise present. Therefore, it is important to reduce the
amount of noise that gets coupled to the inputs. Avoid running
any digital traces near the analog inputs.
Due to the high bandwidth of the AD9887, sometimes low-pass
filtering the analog inputs can help to reduce noise. (For many
applications, filtering is unnecessary.) Experiments have shown
HSYNC IN
VSYNC IN
COAST
SOG
ACTIVITY
DETECT
SYNC STRIPPER
ACTIVITY
DETECT
NEGATIVE PEAK
CLAMP
POLARITY
DETECT
COMP
PLL
SYNC
MUX 2
MUX 3
MUX 4
ACTIVITY
DETECT
HSYNC
COAST
POLARITY
POLARITY
DETECT
DETECT
that placing a series ferrite bead prior to the 75 Ω termination
resistor is helpful in filtering out excess noise. Specifically, the
part used was the # 2508051217Z0 from Fair-Rite, but each
application may work best with a different bead value. Alternately,
placing a 100 Ω to 120 Ω resistor between the 75 Ω termination
resistor and the input coupling capacitor can also be beneficial.
Digital Interface Inputs
Each differential input pair (R
should be routed together using 50 Ω strip line routing tech-
niques and should be kept as short as possible. No other
components should be placed on these inputs; for example, no
clamping diodes. Every effort should also be made to route
these signals on a single layer (component layer) with no vias.
Power Supply Bypassing
It is recommended to bypass each power supply pin with a
0.1 µF capacitor. The exception is in the case where two or
more supply pins are adjacent to each other. For these group-
ings 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 AD9887,
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.
MUX 1
GENERATOR
CLOCK
SYNC SEPARATOR
INTEGRATOR
1/S
PIXEL CLOCK
HSYNC OUT
XO
AD9887
VSYNC
+, R
XO
–, R
XC
+, R
SOG OUT
HSYNC OUT
VSYNC OUT
XC
–, etc.)