GS3440 Datasheet, PDF (13/23 Pages) Semtech Corporation – Extended Reach 3G/HD/SD Adaptive Cable Equalizer

4. Detailed Description
The GS3440 is a high-speed BiCMOS IC designed to equalize serial digital signals.
The GS3440 can equalize 3Gb/s, HD and SD serial digital signals, and will typically
equalize up to 210m of Belden 1694A cable at 2.97Gb/s, 300m at 1.485Gb/s, and 550m at
270Mb/s. The GS3440 can be powered from a single +3.3V DC power supply, and is
footprint-compatible with Semtech’s GS2974A, GS2974B, GS2984, and GS2994
equalizers. When DC coupling the output of a device to a 1.2V CML load, the GS3440
typically consumes 180mW of power.
4.1 Serial Digital Inputs
The received serial data signal is connected to the input pins (SDI/SDI) in either a
differential or single-ended configuration. AC-coupling of the inputs is recommended,
because the SDI and SDI inputs are internally biased to approximately 1.71V.
4.2 Automatic (Adaptive) Cable Equalization
The input signal passes through a variable gain equalizing stage, whose frequency
response closely matches the inverse of the cable (Belden 1694A) loss characteristic. In
addition, the variation of the frequency response with control voltage imitates the
variation of the inverse cable loss characteristic with cable length ensuring that the
correct amount of gain is automatically applied to the input signal for any cable length
within the supported ranges.
The equalized signal is DC-restored, effectively restoring the logic threshold of the
equalized signal to its correct level independent of shifts due to AC-coupling.
4.3 Differential Digital Data Output
The digital data output signals (DDO/DDO) have a nominal output voltage swing of
either 850mV_ppd or 425mV_ppd, as set by the OP_CTL pin. Table 4-1 shows the typical
output common mode voltage levels related to the two output swing options and the
chosen coupling (DC vs. AC).
Table 4-1: Typical Common Mode Output Voltage Levels
Supply Voltage
(VCC_O)
3.3V
2.5V
1.8V
1.2V
425mV_ppd Swing
425mV_ppd Swing
850mV_ppd Swing
850mV_ppd Swing
(DC-coupled Output) (AC-coupled Output) (DC-coupled Output) (AC-coupled Output)
3.2V
2.4V
1.7V
1.1V
3.1V
2.3V
1.6V
1.0V
3.1V
2.3V
1.6V
1.0V
2.9V
2.1V
1.4V
0.8V
GS3440 Adaptive Cable Equalizer
Final Data Sheet
Rev. 2
December 2012
13 of 23
Proprietary and Confidential