GS2984 Adaptive Cable Equalizer

Data Sheet

50985 - 3

March 2010

11 of 20

4.2 Cable Equalization

The input signal passes through a variable gain equalizing stage, whose frequency

response closely matches the inverse of the cable 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.

The edge energy of the equalized signal is monitored by a detector circuit which

produces an error signal corresponding to the difference between the desired edge

energy and the actual edge energy. This error signal is integrated by both an internal and

an external AGC filter capacitor providing a steady control voltage for the gain stage. As

the frequency response of the gain stage is automatically varied by the application of

negative feedback, the edge energy of the equalized signal is kept at a constant level

which is representative of the original edge energy at the transmitter. The equalized

signal is also DC restored, effectively restoring the logic threshold of the equalized signal

to its correct level independent of shifts due to AC coupling.

4.3 Serial Digital Outputs

single-ended when terminated with 50Ω as shown in Figure 4-1.

Figure 4-1: Typical Output Voltage Levels (for 3.3V Common Mode)

50

50

SDO

SDO

+200mV

-200mV

typical

+200mV

-200mV

typical