GS2993 Datasheet, PDF (14/23 Pages) Gennum Corporation – Automatic power-down on loss of signal

Table 4-1: Typical Output Voltage Levels
Supply Voltage -
Output Driver
1.8V
1.2V
400mV_p-p Swing
400mV_p-p Swing
800mV_p-p Swing
800mV_p-p Swing
(DC-coupled Output) (AC-coupled Output) (DC-coupled Output) (AC-coupled Output)
1.7V
1.1V
1.6V
1V
1.6V
1V
1.4V
0.8V
4.4 Programmable Squelch Adjust (SQ_ADJ)
The GS2993 incorporates a programmable Squelch Adjust (SQ_ADJ) threshold.
This feature can be useful in applications where there are multiple input channels using
the GS2993 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, 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 may be left
unconnected. Figure 4-1 shows the relationship between the SQ_ADJ voltage and cable
length at which CD will assert or de-assert.
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: SQ_ADJ is designed to operate when the device is in manual sleep mode. In this
situation, CD should not be connected to SLEEP.
3.2
3.0
2.8
2.6
2.4
2.2
2.0
0
50 100 150 200 250 300 350 400 450
Cable Length (m)
Figure 4-1: SQ_ADJ vs. Cable Length (VCC=3.3V, room temperature, 800mV launch swing)
4.5 Carrier Detect, Sleep, and Auto-Sleep
The GS2993 includes a SLEEP input pin, which allows the application interface to put the
GS2993 into a low-power sleep mode, consuming less than 30mW. Set the SLEEP pin
HIGH to place the chip in its sleep state. In this mode, the Carrier Detect output will still
function in order to detect valid Serial Digital Input.
GS2993 Dual Output Adaptive Cable Equalizer
Data Sheet
53966 - 4
August 2012
14 of 23
Propietary & Confidential