GS2993 Dual Output Adaptive Cable Equalizer

Data Sheet

53966 - 4

August 2012

14 of 23

Propietary & Confidential

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.

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.

1.8V

1.7V

1.6V

1.6V

1.4V

1.2V

1.1V

1V

1V

0.8V

Table 4-1: Typical Output Voltage Levels

Supply Voltage -

Output Driver

(DC-coupled Output)

(AC-coupled Output)

(DC-coupled Output)

(AC-coupled Output)

3.2

3.0

2.8

2.6

2.4

2.2

2.0

Cable Length (m)

0

50 100 150 200 250 300 350 400 450