LMH0394_15 Datasheet, PDF (12/35 Pages) Texas Instruments – 3G HD/SD SDI Low Power Extended Reach Adaptive Cable Equalizer

LMH0394
SNLS312M – AUGUST 2010 – REVISED JULY 2015
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Feature Description (continued)
In pin mode, CD and MUTE may be tied together to automatically mute the output when no input signal is
present.
7.3.4 Input Interfacing
The LMH0394 accepts single-ended input. The input must be AC coupled. The Functional Block Diagram shows
the typical configuration for a single-ended input. The unused input must be properly terminated as shown in
Figure 8 or Figure 9.
The LMH0394 can be optimized for different launch amplitudes through the SPI (see Launch Amplitude
Optimization in the SPI Register Access section).
The LMH0394 correctly handles equalizer pathological signals for standard definition and high definition serial
digital video, as described in ST RP 178 and RP 198, respectively.
7.3.5 Output Interfacing
SDO and SDO together are internally terminated 100-Ω LVDS outputs. These outputs can be DC coupled to
most common differential receivers.
The default output common-mode voltage (V_OS) is 1.2 V. The output common-mode voltage may be adjusted
through the SPI in 200 mV increments, from 0.8 V to 1.2 V (see Output Driver Adjustments and De-emphasis
Setting in the SPI Register Access section). When the output common mode is supply referenced, the common-
mode voltage is about 1.35 V (for 700 mV_P-P differential swing). This adjustable output common-mode voltage
offers flexibility for interfacing to many types of receivers.
The default differential output swing (V_SSP-P) is 700 mV_P-P. The differential output swing may be adjusted through
the SPI. Valid options are 400, 600, 700, or 800 mV_P-P (see Output Driver Adjustments and De-emphasis Setting
in the SPI Register Access section).
The LMH0394 output must be DC coupled to the input of the receiving device where possible. 100-Ω differential
transmission lines must be used to connect between the LMH0394 outputs and the input of the receiving device.
The LMH0394 output must not be DC coupled to CML inputs. If there are strong pullup resistors (that is, 50 Ω) at
the receiving device, AC coupling must be used. The value of these AC-coupling capacitors must be large
enough (typically 4.7 µF) to accommodate for the SD pathological video pattern.
Figure 8 shows an example of a DC-coupled interface between the LMH0394 and LMH0346 SDI reclocker. The
differential transmission line must be terminated with a 100-Ω resistor at the receiving device 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 single 100-Ω resistor.
Figure 9 shows an example of a DC-coupled interface between the LMH0394 and LMH0356 SDI reclocker. The
LMH0356 inputs have internal 50-Ω terminations (100-Ω differential) to terminate the transmission line, so no
additional components are required.
The LMH0394 output driver is equipped with programmable output de-emphasis to minimize inter-symbol
interference caused by the loss dispersion from driving signals across PCB traces (see Output Driver
Adjustments and De-emphasis Setting in the SPI Register Access section). De-emphasis works with all
combinations of output common-mode voltage and output voltage swing settings to support DC coupling to the
receiving device.
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