GS1574 Data Sheet
28854 - 5 May 2007 11 of 18
4. Detailed Description
The GS1574 is a high speed bipolar IC designed to equalize serial digital signals.
The GS1574 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 GS1574 is powered from a single +3.3V power supply and consumes
approximately 270mW 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.
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. The digital output signals have a nominal voltage of 750mV
pp
differential,
or 375mV
pp
single ended when terminated with 50Ω as shown in Figure 4-1.
