GS9024 Data Sheet
5. Detailed Description
The GS9024 Automatic Cable Equalizer is a bipolar integrated circuit designed to
equalize serial digital data signals between 30Mbps and 622Mbps. Powered from
a single +5V or -5V supply, the device consumes approximately 240mW of power.
The serial data signal is connected to the input pins (SDI/SDI) either differentially
or single ended. The input signal passes through a variable gain equalizing stage
whose frequency response closely matches the inverse 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 gain stage
provides up to 40dB of gain at 200MHz which will typically result in equalization of
greater than 350m at 270Mb/s of Belden 8281 cable.
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 an external
differential AGC filter capacitor (AGC+/AGC-) 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 DC restored, thereby restoring its logic threshold to its
corrective level regardless of shifts due to AC coupling. The digital output signals
have PECL voltage levels (800mV) and are available at pins SDO and SDO.
5.1 Output HIGH Z
A HIGH Z pin allows the data outputs to be put into a high impedance state which
disconnects them from the output traces. This feature is ideal for input expansion
in router applications as it eliminates the need for input muxes or crosspoints.
NOTE: The high impedance feature will only take effect if the device outputs are
not muted.
5.2 Signal Strength Indication/Carrier Detect
The GS9024 incorporates an analog signal strength indicator/carrier detect output
(SSI/CD) which indicates both the presence of a carrier and the amount of
equalization applied to the signal. The voltage output of this pin versus cable length
(signal strength) is shown in Figure . With 0m of cable (800mV input signal levels),
the SSI/CD output voltage is approximately 4.5V.
As the cable length increases, the SSI/CD voltage decreases linearly providing
accurate correlation between the SSI/CD voltage and cable length.
521-70-10 February 2005
11 of 16
GENNUM [ GENNUM CORPORATION ]
