MAX3802 Datasheet, PDF (9/12 Pages) Maxim Integrated Products – 3.2Gbps Quad Adaptive Cable Equalizer with Cable Driver

3.2Gbps Quad Adaptive Cable Equalizer
with Cable Driver
dynamically adjusts the equalizer to maintain the cor-
rect 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.
_IN_+
_IN_-
V_CC
50Ω
50Ω
MAX3802
ESD
STRUCTURES
Figure 2. CML Input Structure
V_CC
MAX3802
62.5Ω
62.5Ω
ESD
STRUCTURES
_OUT_+
_OUT_-
Figure 3. CML Output Structure
Flat-Response and Skin-Effect
Compensation Amplifiers
The buffered input waveform is fed equally to two
amplifiers—the flat-response amplifier and the skin-
effect compensation amplifier. The flat-response ampli-
fier has a constant gain over the entire frequency range
of the device, and the skin-effect compensation amplifi-
er 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 pro-
portional to the square root of the frequency. The out-
put currents from the amplifiers are supplied to the
current-steering network.
Current-Steering Network
The function of the current-steering network is to com-
bine adjustable quantities of the output currents from
the flat-response and skin-effect compensation ampli-
fiers in order to achieve a desired current ratio. The
ratio adjustment is controlled by the dual power-detec-
tor 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
attenuators are combined at the summing node and
then fed to the output-limiting amplifier and the feed-
back 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 Amplifier
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.maxim-ic.com) for addi-
tional application information.
Selecting R_MOD
The cable driver output amplitude can be adjusted by
connecting 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
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