GENNUM CORPORATION

521 - 70 - 06

6

Fig. 9 Output Data Waveform at 270Mb/s, 300m

Fig. 10 Output Data Waveform at 540Mb/s, 200m

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.

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.

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 11. 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.

When the signal strength decreases to the level set at the

"Carrier Detect Threshold Adjust" pin, the SSI/CD voltage

goes to a logic "0" state (0.8V) and can be used to drive

other TTL/CMOS compatible logic inputs. In addition, when

loss of carrier is detected the SDO/SDO outputs are muted

(set to a known static state).