Datasheet

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1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
CLI (V)
BELDEN 1694A CABLE LENGTH (m)
LMH0034
www.ti.com SNLS213H –JANUARY 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. Cable Length Indicator (CLI) is derived from this block.
The Carrier Detect / Mute block generates the carrier detect signal and controls the mute function of the output.
This block utilizes the bi-directional CD/MUTE signal along with Mute Reference (MUTE
REF
).
The Output Driver produces SDO and SDO.
CABLE LENGTH INDICATOR (CLI)
The cable length indicator provides a voltage to indicate the length of cable being equalized. The CLI voltage
decreases as the cable length increases. Figure 2 shows the typical CLI voltage vs. Belden 1694A cable length.
Note: CLI is only valid when an input signal is present.
Figure 2. CLI vs. Belden 1694A Cable Length
MUTE REFERENCE (MUTE
REF
)
The mute reference 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 / MUTE (CD/MUTE)
Carrier Detect / Mute is bi-directional, serving as both a carrier detect (output function) and mute (input function).
When used as an output, CD/MUTE determines if a valid signal is present at the LMH0034 input. If MUTE
REF
is
used, the carrier detect threshold will be altered accordingly. CD/MUTE provides a high voltage when no signal is
present at the LMH0034 input, and the outputs are automatically muted. CD/MUTE is low when a valid input
signal has been detected, and the outputs are automatically enabled.
As an input, CD/MUTE can be used to override the carrier detect and manually mute or enable the LMH0034
outputs. Applying a high input to CD/MUTE will mute the LMH0034 outputs. Applying a low input will force the
outputs to be active regardless of the length of cable or the state of MUTE
REF
.
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