Datasheet

LMH0044
www.ti.com SNLS216E –APRIL 2006–REVISED APRIL 2013
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 differential 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 Control 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 applying 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.
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 threshold 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 active.
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 input. The input must be AC coupled. Transformer
coupling is not supported.
The LMH0044 correctly handles equalizer pathological signals for standard definition and high definition serial
digital video, as described in SMPTE RP 178 and RP 198, respectively.
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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