Data Sheet

AD8128

Rev. A | Page 11 of 12

AD8128

HPF

HPF

LPF

AD8128

HPF

HPF

LPF

+

+

VS+

VS–

1µF

0.01µF

VS+

VS+

1µF

0.01µF

VS+

VS+

1µF

0.01µF

VS–

VS–

1µF

0.01µF

VS–

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 AD8128 devices 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 must 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 pad on the underside of the

body. To achieve the specified thermal resistance, it must have a

good thermal connection to one of the PCB planes. The

exposed pad 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 device.

LAYOUT AND POWER SUPPLY DECOUPLING

CONSIDERATIONS

Standard high speed PCB layout practices must be adhered

to when designing with the AD8128. A solid ground plane is

recommended and good wideband power supply decoupling

networks must 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 device. Additionally,

a KVM application specific evaluation board is available. This

evaluation board consists of six AD8128 devices 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.