LMH0384 Datasheet, PDF (7/16 Pages) National Semiconductor (TI) – 3 Gbps HD/SD SDI Extended Reach and Configurable Adaptive Cable Equalizer

Block Diagram (Pin Mode)
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 block generates the carrier detect signal
based on the SDI input and an adjustment from the Mute
Reference block.
The SPI Control block uses the MOSI, MISO, SCK, and SS
signals in SPI mode to control the SPI registers. SPI_EN se-
lects between SPI mode and pin mode. In pin mode, SPI_EN
is driven logic low.
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. The applied voltage must be greater than the
MUTE_REF floating voltage (typically 1.3V) in order to change
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the CD threshold. As the applied MUTE_REF voltage is in-
creased, the amount of cable that can be equalized before
carrier detect is de-asserted and the outputs are muted is de-
creased. MUTE_REF may be left unconnected or connected to
ground for normal CD operation.
CARRIER DETECT (CD) AND MUTE
Carrier detect CD indicates if a valid signal is present at the
LMH0384 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 LMH0384 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 LMH0384
outputs by forcing the output to a logic zero. 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.
AUTO SLEEP
The auto sleep mode allows the LMH0384 to power down
when no input signal is detected. If the AUTO SLEEP pin is
set high, the LMH0384 goes into a deep power save mode
when no signal is detected. The device powers on again once
an input signal is detected. 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
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