AD8114AST Analog Devices Inc, AD8114AST Datasheet - Page 25

• Manufacturer Part Number: AD8114AST
• Description: IC VIDEO CROSSPOINT SWIT 100LQFP
• Manufacturer: Analog Devices Inc

Specifications of AD8114AST

• Rohs Status: RoHS non-compliant
• Function: Video Crosspoint Switch
• Circuit: 1 x 16:16
• Voltage Supply Source: Dual Supply
• Voltage - Supply, Single/dual (±): ±4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 100-LQFP
• Array Configuration: 16x16
• Number Of Arrays: 1
• Screening Level: Industrial
• Pin Count: 100
• Package Type: LQFP
• Power Supply Requirement: Dual
• Lead Free Status / RoHS Status: Not Compliant

PCB LAYOUT
Extreme care must be exercised to minimize additional
crosstalk generated by the system circuit board(s). The areas
that must be carefully detailed are grounding, shielding, signal
routing, and supply bypassing.
The packaging of the AD8114/AD8115 is designed to help keep
the crosstalk to a minimum. Each input is separated from each
other input by an analog ground pin. All of these AGNDs
should be directly connected to the ground plane of the circuit
board. These ground pins provide shielding, low impedance
return paths, and physical separation for the inputs. All of these
help to reduce crosstalk.
Each output is separated from its two neighboring outputs by an
analog supply pin of one polarity or the other. Each of these
analog supply pins provides power to the output stages of only
the two nearest outputs. These supply pins provide shielding,
physical separation, and a low impedance supply for the
outputs. Individual bypassing of each of these supply pins with a
0.01 µF chip capacitor directly to the ground plane minimizes
high frequency output crosstalk via the mechanism of sharing
common impedances.
Each output also has an on-chip compensation capacitor that is
individually tied to the nearby analog ground pins AGND00
through AGND07. This technique reduces crosstalk by
preventing the currents that flow in these paths from sharing a
common impedance on the IC and in the package pins. These
AGNDxx signals should all be connected directly to the ground
plane.
The input and output signals will have minimum crosstalk if
they are located between ground planes on layers above and
below, and separated by ground in between. Vias should be
located as close to the IC as possible to carry the inputs and
outputs to the inner layer. The only place the input and output
signals surface is at the input termination resistors and the
output series back-termination resistors. These signals should
also be separated, to the extent possible, as soon as they emerge
from the IC package.
Rev. B | Page 25 of 32
Optimized for video applications, all signal inputs and outputs
are terminated with 75 Ω resistors. Stripline techniques are used
to achieve a characteristic impedance of 75 Ω on the signal
input and output lines. Figure 50 shows a cross section of one of
the input or output tracks along with the arrangement of the
PCB layers. It should be noted that unused regions of the four
layers are filled up with ground planes. As a result, the input
and output traces, in addition to having controlled impedances,
are well shielded.
The board has 32 BNC type connectors: 16 inputs and 16 outputs.
The connectors are arranged in a crescent around the device. As
can be seen from Figure 53, this results in all 16 input signal
traces and all 16 signal output traces having the same length.
This is useful in tests such as all-hostile crosstalk where the
phase relationship and delay between signals needs to be
maintained from input to output.
The three power supply pins AVCC, DVCC and AVEE should
be connected to good quality, low noise, ±5 V supplies. Where
the same ±5 V power supplies are used for analog and digital,
separate cables should be run for the power supply to the
evaluation board’s analog and digital power supply pins.
As a general rule, each power supply pin (or group of adjacent
power supply pins) should be locally decoupled with a 0.01 µF
capacitor. If there is a space constraint, it is more important to
decouple analog power supply pins before digital power supply
pins. A 0.1 µF capacitor, located reasonably close to the pins,
can be used to decouple a number of power supply pins. Finally
a 10 µF capacitor should be used to decouple power supplies as
they come onto the board.
b = 0.0514"
(1.3mm)
Figure 50. Cross Section of Input and Output Traces
a = 0.008"
(0.2mm)
w = 0.008"
(0.2mm)
h = 0.025"
(0.63mm)
t = 0.00135" (0.0343mm)
AD8114/AD8115
TOP LAYER
SIGNAL LAYER
POWER LAYER
BOTTOM LAYER