Datasheet

frequency bands and dynamically adjusts the equalizer to
maintain the correct power ratio.
CML Input and Output Buffers
The input and output buffers are implemented using CML.
Equivalent circuits are shown in Figures 2 and 3. For details
on interfacing with CML, refer to Maxim Application Note
HFAN-01.0, Interfacing Between CML, PECL, and LVDS.
Flat-Response and Skin-Effect
Compensation Ampliers
The buffered input waveform is fed equally to two
amplifiers—the flat-response amplifier and the skineffect
compensation amplifier. The flat-response amplifier has
a constant gain over the entire frequency range of the
device, and the skin-effect compensation amplifier has a
gain characteristic that approximates the inverse of the
skin-effect attenuation in copper cable. The skin-effect
attenuation, in dB per unit length, is proportional to the
square root of the frequency. The output currents from the
amplifiers are supplied to the current-steering network.
Current-Steering Network
The function of the current-steering network is to combine
adjustable quantities of the output currents from the flat-
response and skin-effect compensation amplifiers in order
to achieve a desired current ratio. The ratio adjustment is
controlled by the dual power-detector feedback loop.
The current-steering network is implemented with a pair
of variable attenuators that feed into a current-summing
node. The variable attenuators are used to attenuate
the output currents of the flat-response and skin-effect
compensation amplifiers under control of the dual power-
detector feedback loop. The outputs of the two attenua-
tors are combined at the summing node and then fed to
the output-limiting amplifier and the feedback loop.
Dual Power-Detector Feedback Loop
The outputs of the current-steering network are applied
to the inputs of 200MHz and 600MHz power detectors.
The outputs of the power detectors are applied to the
loop-filter amplifier. This amplifier controls the variable
attenuators in the current-steering network.
Output Limiting Amplier
The output limiting amplifier amplifies the signal from the
current-steering network to achieve the specified output
voltage swing.
Applications Information
Refer to Maxim Application Note HFDN-10.0, Equalizing
Gigabit Copper Cable Links with the MAX3800 (available
at www.maximintegrated.com) for additional application
information.
Selecting R
MOD
The cable driver output amplitude can be adjusted by con-
necting a resistor (R
MOD
) with a value from 10kΩ to 20kΩ
between the RMOD_ pin and ground. The exact output
amplitude of the driver is dependent on several factors.
Figure 2. CML Input Structure
Figure 3. CML Output Structure
_IN_-
_IN_+
ESD
STRUCTURES
V
CC
50Ω
50Ω
MAX3802
ESD
STRUCTURES
62.5Ω 62.5Ω
_OUT_-
_OUT_+
V
CC
MAX3802
MAX3802 3.2Gbps Quad Adaptive Cable Equalizer
with Cable Driver
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