LMH0384 Datasheet, PDF (14/29 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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Programming (continued)
7.5.5 Cable Length Indicator (CLI)
The Cable Length Indicator (CLI) provides an indication of the length of cable attached to the input. CLI is
accessible through bits [7:3] of SPI register 03h. The 5-bit CLI ranges in decimal value from 0 to 25 (“00000” to
“11001” binary) and increases as the cable length is increased. Figure 9 shows typical CLI values vs. Belden
1694A cable length. CLI is valid for Belden 1694A cable lengths of up to 140 m at 2.97 Gbps, 200 m at 1.485
Gbps, and 400 m at 270 Mbps.
30
25
20
15
10
5
0
0 50 100 150 200 250 300 350 400
BELDEN 1694A CABLE LENGTH (m)
Figure 9. CLI vs. Belden 1694A Cable Length
7.5.6 Application of CLI: Extending 3G Reach
An application of CLI is to extend the 3G reach in systems which have margin in the jitter budget. This allows for
additional cable reach at 2.97 Gbps at the expense of slightly higher output jitter. The extended 3G reach mode
provides 15m of additional Belden 1694A cable reach, with an increase of output jitter at this longer cable length
of 0.05 to 0.1 UI.
The extended 3G reach mode is accessible through bit 2 of SPI register 00h. In order to achieve longer 3G cable
reach while still maintaining the performance at HD and SD data rates, a state machine can be implemented as
shown in Figure 10. (Note: If this procedure is not followed, the maximum equalizable cable lengths for HD and
SD data rates will be limited to less than what can be achieved in normal mode).
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