GS3440 Adaptive Cable Equalizer

Final Data Sheet

Rev. 2

December 2012

13 of 23

Proprietary and Confidential

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

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)

(DC-coupled Output)

(AC-coupled Output)

(DC-coupled Output)

(AC-coupled Output)

3.3V

3.2V

3.1V

3.1V

2.9V

2.5V

2.4V

2.3V

2.3V

2.1V

1.8V

1.7V

1.6V1.6V1.4V

1.2V

1.1V

1.0V

1.0V

0.8V