LMH0074_1 NSC [National Semiconductor], LMH0074_1 Datasheet - Page 3

• Manufacturer Part Number: LMH0074_1
• Description: Replacing the CLC012 Adaptive Cable Equalizer with the LMH0074
• Manufacturer: NSC [National Semiconductor]

OUTPUT INTERFACE
The CLC014 outputs are open collector and require 75Ω
pullups to 5V to generate an output voltage. This structure has
some limitations when interfacing to non-5V systems. The
CLC014 outputs are essentially cut off if the DO output volt-
age drops below V
DC-coupling to other 3.3V devices.
The LMH0074 provides much more flexibility. The LMH0074
outputs are CML with internal 50Ω pullups to 3.3V. They may
be DC coupled to many more types of inputs, including the
LMH0026 or LMH0036 reclocker and the LMH0001 cable
driver. Typically only a far-end differential termination (a sim-
ple resistor) is required. If the LMH0074 output common mode
voltage is not compatible with the input common mode volt-
age of the receiving device, the outputs may be AC coupled
as shown in
V
AEC CAPACITOR VALUE
The CLC014 AEC capacitor is typically 100 pF and may be
changed to change the adaptive loop time constant. For the
LMH0074, the AEC capacitor should be 1.0 µF only. The
LMH0074 was designed and optimized for a 1.0 µF AEC ca-
pacitor and it should not be changed.
CARRIER DETECT AND MUTE
In CLC014 applications, the carrier detect pin (CD) is typically
tied to the MUTE pin to inhibit the output when there is no
LMH0074 Enhancements over the
CLC014
The LMH0074 is a solid upgrade and good replacement for
the CLC014. It is designed in a newer, more advanced pro-
cess. The LMH0074 offers lower power, better ESD protec-
tion, a more flexible output interface, and new features such
CC
.
Figure
CC
2. The outputs do not require pullups to
-1.6V (typically 3.4V), so this prevents
FIGURE 4. LMH0074 Differential Twisted Pair Input Interface
FIGURE 3. CLC014 Differential Twisted Pair Input Interface
3
input signal. For the LMH0074 this can be done as well. The
only difference is that the polarity of the carrier detect and
mute is reversed for the LMH0074; the carrier detect pin,
CD , is active low, and the mute pin, MUTE, is active high.
OTHER FEATURES
The CLC014 has an Output Eye Monitor which shows the
equalized eye pattern prior to the output comparator. This
feature is not included in the LMH0074; however, the
LMH0074 includes features in addition to those in CLC014,
such as the MUTE
the threshold for CD and (with CD tied to MUTE) determines
the amount of cable to equalize before muting the outputs.
This may be useful to limit the maximum cable length that can
be equalized, or for very noisy environments where CD would
need to be less sensitive. BYPASS passes the input signal
through to the output with no equalization. This may be useful
for very low data rate applications.
100Ω DIFFERENTIAL TWISTED PAIR CABLE
APPLICATIONS
The equalizers can both be used for differential twisted pair
cable applications.
input interface for the CLC014 and
ential twisted pair input interface for the LMH0074.
as the ability to bypass equalization. The LMH0074’s smaller,
space-saving package allows for more compact designs. The
PCB layout is simpler as the LMH0074 requires less PCB
components overall than the CLC014. In addition, the
LMH0074’s pin compatibility with HD-SDI and 3G-SDI equal-
izers offers an easy upgrade path and allows future-proof
designs.
REF
Figure 3
and BYPASS functions. MUTE
30105903
30105904
shows the differential twisted pair
Figure 4
shows the differ-
www.national.com
REF
sets