GS3140 Datasheet, PDF (13/40 Pages) Semtech Corporation – Multi-Rate Adaptive 3G SDI Equalizer

4.3 Cable Length Indication
The GS3140 reports the input signal strength through the CABLE_LENGTH_INDICATOR
bits in the STATUS_REG_0 register, accessible through the device's host interface. The
Cable Length Indication (CLI) is a simple, numeric value in the range from 0_h to EF_h. This
number can be approximated as a cable length in meters by applying one of the cable
scaling factors shown in Table 4-1 below for some commonly used coaxial cables.
Table 4-1: Cable Length Scaling Factors
Cable Type
Belden 1694A
Belden 8281
CLI Scaling Factor
2.5
1.77
The CLI readout value has a multiplication resolution of 1 between 0_h and 7F_h. In the
range from 80_h to EF_h the measurement resolution of CLI is reduced, and CLI value
increments by a multiple of 3.
Note: Any additional loss due to other transmission line elements (such as patch panels,
barrels, extra connectors, etc.), also translates to an equivalent cable length based on
the cable scaling factor.
4.4 Programmable Squelch Threshold
The GS3140 features a programmable squelch threshold, set through the device's host
interface. It impacts Loss of Signal (LOS) status. As shown in Figure 4-1, squelch only
affects the LOS status when bits AUTO_BYPASS, BYPASS, and SLEEP[1:0] in
EQ_CONF_REG_0 are all 0.
The device continually compares the strength of the input signal as set in the
CABLE_LENGTH_INDICATOR bits in the STATUS_REG_0 register to the squelch
threshold set by the SQUELCH_THRESHOLD bits in the EQ_CONF_REG_1 register.
When the value reported by the CABLE_LENGTH_INDICATOR bits exceeds the value
programmed by the SQUELCH_THRESHOLD bits by 3 or more, the Loss of Signal (LOS)
status bit in the STATUS_REG_0 register is set to 1.
When the value reported by the CABLE_LENGTH_INDICATOR bits falls below the value
programmed by the SQUELCH_THRESHOLD bits by 3 or more, the Loss of Signal (LOS)
status bit in the STATUS_REG_0 register is set to 0.
This ±2 hysteresis around the SQUELCH_THRESHOLD setting avoids chattering of the
LOS bit status for input signal strengths right around the threshold setting.
By default, the squelch threshold is set to the maximum possible level, and therefore
squelch is disabled.
GS3140
Final Data Sheet
PDS-060939
Rev.1
May 2015
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