LMH0044_09 Datasheet, PDF (5/8 Pages) National Semiconductor (TI) – SMPTE 292M / 259M Adaptive Cable Equalizer

Block Diagram
Device Operation
BLOCK DESCRIPTION
The Equalizer Filter block is a multi-stage adaptive filter. If
Bypass is high, the equalizer filter is disabled.
The DC Restoration / Level Control block receives the dif-
ferential signals from the equalizer filter block. This block
incorporates a self-biasing DC restoration circuit to fully DC
restore the signals. If Bypass is high, this function is disabled.
The signals before and after the DC Restoration / Level Con-
trol block are used to generate the Automatic Equalization
Control (AEC) signal. This control signal sets the gain and
bandwidth of the equalizer filter. The loop response in the
AEC block is controlled by an external 1µF capacitor placed
across the AEC+ and AEC- pins.
The Carrier Detect / Mute block generates the carrier detect
signal and controls the mute function of the output. This block
utilizes the CD and MUTE signals along with Mute Reference
(MUTE_REF).
The Output Driver produces SDO and SDO.
MUTE REFERENCE (MUTE_REF)
The mute reference sets the threshold for CD and (with CD
tied to MUTE) determines the amount of cable to equalize
before automatically muting the outputs. This is set by apply-
ing a voltage inversely proportional to the length of cable to
equalize. As the applied MUTE_REF voltage is increased, the
amount of cable that can be equalized before carrier detect is
de-asserted and the outputs are muted is decreased.
MUTE_REF may be left unconnected for maximum equalization
before muting.
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CARRIER DETECT (CD) AND MUTE
Carrier detect CD indicates if a valid signal is present at the
LMH0044 input. If MUTE_REF is used, the carrier detect thresh-
old will be altered accordingly. CD provides a high voltage
when no signal is present at the LMH0044 input. CD is low
when a valid input signal is detected.
MUTE can be used to manually mute or enable SDO and
SDO. Applying a high input to MUTE will mute the LMH0044
outputs. Applying a low input will force the outputs to be ac-
tive.
CD and MUTE may be tied together to automatically mute the
output when no input signal is present.
INPUT INTERFACING
The LMH0044 accepts either differential or single-ended in-
put. The input must be AC coupled. Transformer coupling is
not supported.
The LMH0044 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 SDO and SDO outputs are internally loaded with 50Ω.
They produce a 750 mV_P-P differential output, or a
375 mV_P-P single-ended output.
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