GS1574A Data Sheet

33416 - 5

March 2006

11 of 16

4. Detailed Description

The GS1574A is a high speed BiCMOS IC designed to equalize serial digital

signals.

The GS1574A can equalize both HD and SD serial digital signals, and will typically

equalize greater than 140m of Belden 1694A cable at 1.485Gb/s and 350m at

270Mb/s.

The GS1574A is powered from a single +3.3V power supply and consumes

approximately 215mW of power.

4.1 Serial Digital Inputs

The serial data signal may be connected to the input pins (SDI/SDI) in either a

differential or single ended configuration. AC coupling of the inputs is

recommended, as the SDI and SDI inputs are internally biased at approximately

1.8V.

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