Datasheet

AEC+
Equalizer
Filter
AEC-
MUTE
MUTE
REF
DC
Restoration/
Level Control
Automatic
Equalization
Control
SDI
SDI
SDO
SDO
BYPASS
Output
Driver
6
Carrier
Detect/
Mute
Energy
Detect
Energy
Detect
CD
LMH0074
www.ti.com SNLS277D –AUGUST 2007–REVISED APRIL 2013
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 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 LMH0074 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
LMH0074 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
LMH0074 outputs. Applying a low input will force the outputs to be active.
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