GS3441 Datasheet, PDF (15/25 Pages) Semtech Corporation – Extended Reach 3G/HD/SD Adaptive Cable Equalizer with Dual Outputs

4.4 Programmable Squelch Adjust (SQ_ADJ)
The GS3441 features a programmable Squelch Adjust (SQ_ADJ) threshold.
This feature can be useful in applications where there are multiple input channels using
the GS3441 and the maximum gain can be limited to avoid crosstalk.
The SQ_ADJ pin acts to change the threshold of the Carrier Detect (CD) pin, through
voltage level variances. When the input signal drops below a certain threshold set by
SQ_ADJ, the CD pin will be driven HIGH, indicating that there is not a valid input signal.
In applications where programmable squelch adjust is not required, the SQ_ADJ pin can
be left unconnected.
This feature has been designed for use in applications such as routers, where signal
crosstalk and circuit noise cause the equalizer to output erroneous data when no input
signal is present. The use of a Carrier Detect function with a fixed internal reference
does not solve this problem, since the signal-to-noise ratio on the circuit board could be
significantly less than the default signal detection level set by the on-chip reference.
Note: When using SQ_ADJ to limit the maximum gain of the GS3441, CD should not be
connected to SLEEP.
4.5 Carrier Detect, Sleep, and Auto-Sleep
The Carrier Detect output pin (CD) indicates the presence of a valid signal at the input of
the GS3441. When CD is LOW, the device has detected a valid input on SDI and SDI.
When CD is HIGH, the device has not detected a valid input.
The GS3441 includes a SLEEP input pin, which can be used to put the device into a
low-power sleep mode, consuming less than 35mW. In this mode, the outputs are high
impedance and will be pulled high by the on-chip termination. Set the SLEEP pin HIGH
to place the chip in this low-power state. In this mode, the Carrier Detect output will still
function to facilitate the detection of a valid serial input data signal.
Auto-Sleep is enabled by connecting CD to SLEEP. When connected, the GS3441 will
automatically go into low-power sleep mode when there is a loss of Serial Digital Input
signal.
Note 1: CD will only detect loss of carrier for data rates greater than 19Mb/s.
Note 2: If SQ_ADJ is being used to limit the maximum gain of the device, and the
maximum cable length is exceeded when BYPASS pin is set LOW, the CD pin will be set
HIGH even if a carrier is present.
Note 3: If the CD pin is connected to the SLEEP pin, SQ_ADJ must be either left open, or
connected to ground.
Table 4-2: SLEEP Input Table
SLEEP
0
1
Function
The GS3441 operates normally
The GS3441 enters low-power sleep
mode. CD output remains valid
GS3441 Extended Reach 3G/HD/SD Adaptive Cable
Equalizer with Dual Outputs
Final Data Sheet Rev. 1
GENDOC-056647 May 2013
www.semtech.com
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