AD8123ACPZ Analog Devices Inc, AD8123ACPZ Datasheet - Page 10

• Manufacturer Part Number: AD8123ACPZ
• Description: Triple Equalizer
• Manufacturer: Analog Devices Inc

AD8123
THEORY OF OPERATION
The AD8123 is a unity-gain, triple, wideband, low noise analog
line equalizer that compensates for losses in UTP and coaxial
cables up to 300 meters in length. The 3-channel architecture is
targeted at high resolution RGB applications but can be used in
HD YPbPr applications as well.
Three continuously adjustable control voltages, common
to the RGB channels, are available to the designer to provide
compensation for various cable lengths as well as for variations
in the cable itself. The V
of high frequency peaking. V
used to compensate for frequency and cable-length dependent,
high frequency losses that are present due to the skin effect of
the cable. A second control pin, V
gain to compensate for low frequency flat losses present in the
cable. A third control, V
equalizer poles and can be linearly derived from V
in the Typical Performance Characteristics and Applications
Information sections, for UTP and coaxial cables. Finally, an
output offset adjust control, V
the output dc level.
The AD8123 has a high impedance differential input that makes
termination simple and allows dc-coupled signals to be received
directly from the cable. The AD8123 input can also be used in a
single-ended fashion in coaxial cable applications. For differential
systems that require very high CMRR, a triple differential
receiver, such as the
front of the AD8123.
The AD8123 has a low impedance output that is capable of
driving a 150 Ω load. For systems where the AD8123 has to
drive a high impedance capacitive load, it is recommended that
a small series resistor be placed between the output and load to
buffer the capacitance. The resistor should not be so large as to
reduce the overall bandwidth to an unacceptable level.
AD8143
PEAK
POLE
, is used to move the positions of the
input is used to control the amount
PEAK
or AD8145, can be placed in
OFFSET
GAIN
is the primary control that is
, allows the designer to shift
, is used to adjust broadband
PEAK
, as illustrated
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The AD8123 is designed such that systems that use short-to-
medium-length cables do not pay a noise penalty for excess gain
that they do not require. The high gain is only available for
longer length systems where it is required. This feature is built
into the V
Two comparators are provided on-chip that can be used for
sync pulse extraction in systems that use sync-on-common
mode encoding. Each comparator has very low output impedance
and can therefore be used in a source-only cable termination
scheme by placing a series resistor equal to the cable characteristic
impedance directly on the comparator output. Additional
details are provided in the Applications Information section.
INPUT COMMON-MODE VOLTAGE RANGE
CONSIDERATIONS
When using the AD8123 as a receiver, it is important to ensure
that its input common-mode voltage stays within the specified
range. The received common-mode level is calculated by adding
the common-mode level of the driver, the single-ended peak
amplitude of the received signal, the amplitude of any sync
pulses, and the other induced common-mode signals, such as
ground shifts between the driver and the AD8123 and pickup
from external sources, such as power lines and fluorescent
lights. See the Applications Information section for more details.
PEAK
control and is transparent to the user.