AD8128

Rev. 0 | 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 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.