LMH0024 Datasheet, PDF (5/7 Pages) National Semiconductor (TI) – 3.3V SMPTE 259M / 344M Adaptive Cable Equalizer

Block Diagram
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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 dis-
abled.
The signals before and after the DC Restoration / Level
Control block are used to generate the Automatic Equal-
ization 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 Output Driver produces SDO and SDO. SDO and SDO
may be force to mute by activating MUTE.
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.
MUTE
MUTE can be used to manually mute or enable the
LMH0024 outputs. MUTE must be tied to a low-level input or
ground for SDO and SDO to be active. Applying a high input
to MUTE will mute the LMH0024 outputs.
INPUT INTERFACING
The LMH0024 accepts either differential or single-ended
input. The input must be AC coupled. Transformer coupling
is not supported.
The LMH0024 correctly handles equalizer pathological sig-
nals for standard definition serial digital video, as described
in SMPTE RP 178.
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.
Application Information
PCB LAYOUT RECOMMENDATIONS
Please refer to the following Application Note for the CLC034
on National’s website: AN-1372, “CLC034 PCB Layout
Techniques.” The PCB layout techniques in this application
note apply to the LMH0024 as well.
REPLACING THE GENNUM GS9064
The LMH0024 is footprint compatible with the Gennum
GS9064. Pin 16 (MUTE) of the LMH0024 must be connect to
ground for correct operation.
SUPPLY CURRENT VS. CABLE LENGTH
The supply current (I_CC) depends on the amount of cable
being equalized. The current is highest for short cable and
decreases as the cable length is increased. Figure 1 shows
supply current vs. Belden 1694A cable length for 270 Mbps
data.
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