GS6152 Datasheet, PDF (19/80 Pages) Semtech Corporation – Multi-Rate 6G UHD-SDI

4.3.1 Loss of Signal Detection
LOS (Loss of Signal) detection is an active HIGH output available to the application on
any of the GPIO[3:0] multi-function status and control pins. It is selected for output using
the GPIO[3:0]_IO_SELECT and GPIO[3:0]_SELECT bits accessible in the
GPIO_CONTROL_REG_0 and GPIO_CONTROL_REG_1 registers. It is the default output of
the GPIO0 pin.
LOS indicates when the serial digital signal selected by the input selector is invalid. This
function is always active.
Two methods can be used to detect loss of signal: strength (default) and edge. Either
method can be selected with LOS_DETECTION_METHOD bits of register PLL_CONTROL.
When strength detection is used as the method of LOS detection the corresponding
GPIO pin will be HIGH (signal lost) when the input signal amplitude within a predefined
window falls below the threshold set by the bits DDI[0:3]_LOS_THRESHOLD_CONTROL
in the LOS_CONTROL_REG_1 and LOS_CONTROL_REG_2 registers. The LOS threshold
hysteresis can be set by the LOS_HYSTERESIS bits in the LOS_CONTROL_REG_0 register
at address F_h.
The corresponding GPIO pin will be LOW (signal present) when the input signal
amplitude within a predefined window is above the defined threshold.
The method of strength detection is measurement of the average rectified differential
voltage on the input pins. The strength detection method is therefore inherently
dependent on the input signal's eye shape, particularly the rise/fall times of the input
signal relative to the data rate. Additionally, the circuit has a lower bandwidth limit of
operation (20Mb/s) below which it is recommended that the edge detection method is
used. The absolute value of the threshold can be determined for any input swings
according to Equation 4-1 below:
Threshold = ^{1---.--9---m-----V--}₍--D--^×---E--⁽-V-^D----I^D--C--^I--E^[--⁰-_--^.-^.-S³---P^]--^_-E--^L--C-^O---I-^S-F--^_-I--^T_C---^H-_---^R_L---^E-O--^S--S-^H---_-^O--T--^L-H--^D---R-^_---E^C---S^O----H^N----O^T---^R-L---^O-D---^L--₎-⁾----^×-----5---3--
where DEVICE_SPECIFIC_LOS_THRESHOLD specifies the LOS threshold value for a
100mV input swing at SD-rate specific to each device. The other rates scale according to
the fractional relationship given in Figure 4-1 and Figure 4-2 below.
Equation 4-1
GS6152
Final Data Sheet
PDS-060984
Rev.2
July 2015
www.semtech.com
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