AD8128
Rev. 0 | Page 11 of 12
VOFFSET
VGAIN
VPEAK
VOFFSET VGAIN VPEAK
VOUT
VIN+
VIN–
AD8128
HPF
LPF
VOFFSET
VGAIN
VPEAK
VOUT
VIN+
VIN–
AD8128
HPF
LPF
05
69
9-
0
19
+
VS+
VS–
1F
0.01F
VS+
1F
0.01F
VS+
1F
0.01F
VS–
1F
0.01F
VS–
Figure 21. Cascaded AD8128 Configuration
CASCADED APPLICATIONS
To equalize distances longer than the specified 100 meters, the
AD8128 can be cascaded to provide equalization for longer
distances. When combining two AD8128s in series, it is possible to
link the control pins together and use them like a single control
pin for up to 200 meters of equalization.
In this configuration, it is important to note that some key
video specifications can be slightly degraded. By combining two
equalizers in series, specifications such as rise time and settling
time both increase while 3 dB bandwidth decreases slightly.
Also, integrated noise is increased because the second equalizer
adds gain. Subjective testing should be done to determine the
appropriate setting for the three control pins for optimum
equalization.
EXPOSED PAD (EP)
The 8-lead LFCSP has an exposed paddle on the underside of
its body. To achieve the specified thermal resistance, it must
have a good thermal connection to one of the PCB planes. The
exposed paddle must be soldered to a pad on top of the board
connected to an inner plane with several thermal vias. For the
AD8128, this pad must also be electrically connected to ground
to provide a ground reference to the part.
LAYOUT AND POWER SUPPLY DECOUPLING
CONSIDERATIONS
Standard high speed PCB layout practices should be adhered to
when designing with the AD8128. A solid ground plane is
recommended and good wideband power supply decoupling
networks should be placed as close as possible to the supply
pins and control pins. Small surface-mount ceramic capacitors
are recommended for these networks, and tantalum capacitors
are recommended for bulk supply decoupling.
EVALUATION BOARDS
There are two evaluation boards available for easy characterization
of the AD8128. A general-purpose evaluation board consisting
of a single AD8128, with an option of also using a dedicated
receiver, is available for simple characterization of the part.
Additionally, a KVM application specific evaluation board is
available. This evaluation board consists of six AD8128s to
equalize each of the RGB channels up to 200 meters, a 16-pin
26C32 comparator for sync-on-common-mode extract and a
triple op amp to provide additional gain if necessary.