LMH0384 Datasheet, PDF (12/29 Pages) National Semiconductor (TI) – 3 Gbps HD/SD SDI Extended Reach and Configurable Adaptive Cable Equalizer

LMH0384
SNLS308G – APRIL 2009 – REVISED JUNE 2015
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Feature Description (continued)
The LMH0384 output should be DC coupled to the input of the receiving device as long as the common-mode
ranges of both devices are compatible. 100-Ω differential transmission lines should be used to connect between
the LMH0384 outputs and the input of the receiving device where possible. Figure 7 shows an example of a DC-
coupled interface between the LMH0384 and LMH0346 SDI reclocker. All that is required is the 100-Ω differential
termination as shown. The resistor should be placed as close as possible to the LMH0346 input. If desired, this
network may be terminated with two 50-Ω resistors and a center tap capacitor to ground in place of the signal
100-Ω resistor.
Figure 8 shows an example of a DC-coupled interface between the LMH0384 and LMH0356 SDI reclocker. The
LMH0356 inputs have 50-Ω internal terminations (100-Ω differential) to terminate the transmission line, so no
additional components are required.
The LMH0384 allows flexibility when interfacing to low voltage crosspoint switches (that is, 1.8 V) and other
devices with limited input ranges. The LMH0384 outputs can be DC coupled to these devices in most cases,
avoiding the need to AC couple.
The LMH0384 may be AC-coupled to the receiving device when necessary. For example, the LMH0384 outputs
are not strictly compatible with 3.3 V CML and thus should not be connected through 50-Ω resistors to 3.3 V. If
the input common-mode range of the receiving device is not compatible with the output common-mode range of
the LMH0384, then AC coupling is required. Following the AC-coupling capacitors, the signal may have to be
biased at the input of the receiving device.
Coaxial Cable
75:
5.6 nH
1.0 PF
SDI
SDO
1.0 PF ^LMH0384
SDI
SDO
75:
37.4:
100: Differential T-Line
SDI
LMH0346
100:
3G/HD/SD
SDI Reclocker
SDI
Figure 7. DC Output Interface to LMH0346 Reclocker
Coaxial Cable
75:
5.6 nH
1.0 PF
SDI
SDO
LMH0384
1.0 PF
SDI
SDO
75:
37.4:
100: Differential T-Line
SDI0
LMH0356
3G/HD/SD
SDI Reclocker
SDI0
Figure 8. DC Output Interface to LMH0356 Reclocker
7.4 Device Functional Modes
The LMH0384 supports two modes of operation: Pin and SPI Mode. In pin mode the LMH0384 is footprint
compatible with the LMH0344 and legacy SDI equalizers. In the optional SPI mode, the LMH0384 provides
register access to all of its features along with a cable length indicator, programmable output common-mode
voltage and swing, and launch amplitude optimization.
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