LMH0395 Datasheet, PDF (9/21 Pages) Texas Instruments – 3G HD/SD SDI Dual Output Low Power Extended Reach Adaptive Cable Equalizer

CARRIER DETECT (CD) AND MUTE
Carrier detect CD indicates if a valid signal is present at the
LMH0395 input. This signal is logical OR operation of internal
energy detector and MUTE_REF setting (if used). Internal en-
ergy detector detects energy across different data rates. If
MUTE_REF is used, the carrier detect threshold will be altered
accordingly. CD provides a high voltage when no signal is
present at the LMH0395 input. CD is low when a valid input
signal is detected.
MUTE can be used to manually mute or enable the output
drivers. Applying a high input to MUTE will mute the LMH0395
outputs by forcing the output to a logic 1. Applying a low input
will force the outputs to be active.
In pin mode, CD and MUTE may be tied together to automat-
ically mute the output when no input signal is present.
AUTO SLEEP
The auto sleep mode allows the LMH0395 to power down
when no input signal is detected. If the AUTO SLEEP pin is
set high, the LMH0395 goes into a deep power save mode
when no signal is detected. The device powers on again once
an input signal is detected. If the AUTO SLEEP pin is set low,
the LMH0395 will always be on and will not enter power save
mode. The auto sleep functionality can be turned off by setting
AUTO SLEEP low or tying this pin to ground. An additional
auto sleep setting available in SPI mode can be used to force
the equalizer to power down regardless of whether there is
an input signal or not. Auto sleep has precedence over mute
and bypass modes.
In auto sleep mode, the time to power down the equalizer
when the input signal is removed is less than 200 µs and
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 5 ms). The
overall system will be limited only by the settling time constant
of the equalizer adaptation loop.
INPUT INTERFACING
The LMH0395 accepts either differential or single-ended in-
put. The input must be AC coupled. The Typical Application
(Pin Mode) diagram shows the typical configuration for a sin-
gle-ended input. The unused input must be properly termi-
nated as shown.
The LMH0395 can be optimized for different launch ampli-
tudes via the SPI (see LAUNCH AMPLITUDE OPTIMIZA-
TION in the SPI Register Access section).
The LMH0395 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
The LMH0395 dual output differential pairs, SDO0, SDO0,
SDO1, and SDO1 are internally terminated 100Ω LVDS out-
puts. These outputs can be DC coupled to most common
differential receivers.
The default output common mode voltage (V_OS) is 1.2V. The
output common mode voltage may be adjusted via the SPI in
200 mV increments, from 0.8V to 1.2V (see OUTPUT DRIV-
ER ADJUSTMENTS AND DE-EMPHASIS SETTING in the
SPI Register Access section). When the output common
mode is supply referenced, the common mode voltage is
about 1.35V (for 700 mV_P-P differential swing). 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.
Valid options are 400, 600, 700, or 800 mV_P-P (see OUTPUT
DRIVER ADJUSTMENTS AND DE-EMPHASIS SETTING in
the SPI Register Access section).
The LMH0395 output should be DC coupled to the input of
the receiving device where possible. 100Ω differential trans-
mission lines should be used to connect between the
LMH0395 outputs and the input of the receiving device.
The LMH0395 output should not be DC coupled to CML in-
puts. If there are strong pullup resistors (i.e. 50Ω) at the
receiving device, AC coupling should be used. The value of
these AC-coupling capacitors should be large enough (typi-
cally 4.7 µF) to accommodate for the SD pathological video
pattern.
Figure 5 shows an example of a DC-coupled interface be-
tween the LMH0395 and LMH0346 SDI reclocker. The differ-
ential transmission line should be terminated with a 100Ω
resistor at the receiving device as shown. The resistor should
be placed as close as possible to the LMH0346 input. If de-
sired, this network may be terminated with two 50Ω resistors
and a center-tap capacitor to ground in place of the single
100Ω resistor.
Figure 6 shows an example of a DC-coupled interface be-
tween the LMH0395 and LMH0356 SDI reclocker. The
LMH0356 inputs have internal 50Ω terminations (100Ω dif-
ferential) to terminate the transmission line, so no additional
components are required.
The LMH0395 output drivers are equipped with pro-
grammable output de-emphasis to minimize inter-symbol in-
terference caused by the loss dispersion from driving signals
across PCB traces (see OUTPUT DRIVER ADJUSTMENTS
AND DE-EMPHASIS SETTING in the SPI Register Access
section). De-emphasis works with all combinations of output
common mode voltage and output voltage swing settings to
support DC coupling to the receiving device.
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