GS3440 Datasheet, PDF (14/23 Pages) Semtech Corporation – Extended Reach 3G/HD/SD Adaptive Cable Equalizer

4.4 Programmable Squelch Adjust (SQ_ADJ)
The GS3440 features a programmable Squelch Adjust (SQ_ADJ) threshold.
This feature can be useful in applications where there are multiple input channels using
the GS3440 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. When the
input signal drops below the 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 GS3440, 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 GS3440. 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 GS3440 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 GS3440 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 is set LOW, the CD pin will be set to
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 GS3440 operates normally
The GS3440 enters low-power sleep
mode. CD output remains valid
GS3440 Adaptive Cable Equalizer
Final Data Sheet
Rev. 2
December 2012
14 of 23
Proprietary and Confidential