LMH0384 Datasheet, PDF (8/16 Pages) National Semiconductor (TI) – 3 Gbps HD/SD SDI Extended Reach and Configurable Adaptive Cable Equalizer

should not have any impact on the system timing require-
ments. The device will wake up automatically once an input
signal is detected, and the delay between signal detection and
full functionality of the equalizer is negligible (about 1 µs). The
overall system will be limited only by the settling time constant
of the equalizer adaptation loop.
INPUT INTERFACING
The LMH0384 accepts either differential or single-ended in-
put. The input must be AC coupled. The Typical Application
(Pin Mode) diagram on the front page shows the typical con-
figuration for a single-ended input. The unused input must be
properly terminated as shown.
The LMH0384 can be optimized for different launch ampli-
tudes via the SPI (see LAUNCH AMPLITUDE OPTIMIZA-
TION in the SPI Register Access section).
The LMH0384 correctly handles equalizer pathological sig-
nals for standard definition and high definition serial digital
video, as described in SMPTE RP 178 and RP 198, respec-
tively.
OUTPUT INTERFACING
SDO and SDO together are internally terminated 100Ω LVDS
outputs. These outputs can be DC coupled to most common
differential receivers.
The default output common mode voltage (V_OS) is 1.25V. The
output common mode voltage may be adjusted via the SPI in
200 mV increments, from 1.05V to 1.85V (see OUTPUT
DRIVER ADJUSTMENTS in the SPI Register Access sec-
tion). This adjustable output common mode voltage offers
flexibility for interfacing to many types of receivers.
The default differential output swing (V_SSP-P) is 700 mV_P-P.
The differential output swing may be adjusted via the SPI in
100 mV increments from 400 mV_P-P to 800 mV_P-P (see OUT-
PUT DRIVER ADJUSTMENTS in the SPI Register Access
section).
The LMH0384 output should be DC coupled to the input of
the receiving device as long as the common mode ranges of
both devices are compatible. 100Ω differential transmission
lines should be used to connect between the LMH0384 out-
puts and the input of the receiving device where possible.
Figure 4 shows an example of a DC-coupled interface be-
tween the LMH0384 and LMH0346 SDI reclocker. All that is
required is the 100Ω differential termination as shown. The
resistor should be placed as close as possible to the
LMH0346 input. If desired, this network may be terminated
with two 50Ω resistors and a center tap capacitor to ground
in place of the signal 100Ω resistor.
Figure 5 shows an example of a DC-coupled interface be-
tween the LMH0384 and LMH0356 SDI reclocker. The
LMH0356 inputs have 50Ω internal terminations (100Ω dif-
ferential) to terminate the transmission line, so no additional
components are required.
The LMH0384 allows flexibility when interfacing to low voltage
crosspoint switches (i.e. 1.8V) and other devices with limited
input ranges. The LMH0384 outputs can be DC coupled to
these devices in most cases, avoiding the need to AC couple.
The LMH0384 may be AC coupled to the receiving device
when necessary. For example, the LMH0384 outputs are not
strictly compatible with 3.3V CML and thus should not be
connected via 50Ω resistors to 3.3V. If the input common
mode range of the receiving device is not compatible with the
output common mode range of the LMH0384, then AC cou-
pling is required. Following the AC coupling capacitors, the
signal may have to be biased at the input of the receiving de-
vice.
FIGURE 4. DC Output Interface to LMH0346 Reclocker
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FIGURE 5. DC Output Interface to LMH0356 Reclocker
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