GS9024 Data Sheet

521-70-10

February 2005

11 of 16

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.