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Fig. 19 CLI Voltage vs. Belden 1694A Cable Length

Fig. 20 CLI Voltage vs. Belden 8281 Cable Length

DETAILED DESCRIPTION

The GS1504 is a high speed bipolar IC designed to

equalize HD serial digital data at a rate of 1.485Gb/s. The

device can typically equalize greater than 100 meters of

Belden 8281 cable or 150 meters of Belden 1694 cable.

Powered from a single +5V or -5V power supply, the device

consumes approximately 250mW of power

The HD 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 2.7 volts. 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 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 internal 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 400mVpp

differential, or 200mVpp single ended when terminated with

50

Ω as shown in Figure 21.

Fig. 21 Typical Output Voltage Levels

CABLE LENGTH INDICATION/CARRIER DETECT/MUTE

The GS1504 incorporates a versatile analog cable length

indicator (CLI) output and a programmable threshold output

mute (MCLADJ). In addition, a multi-function CD/MUTE pin

allows control of the GS1504 MUTE functionality.

The voltage output of CLI pin is an approximation of the

amount of cable present at the GS1504 input. The CLI

voltage versus cable length (signal strength) is shown in

Figures 19 and 20. With 0m of cable (800mV input signal

levels), the CLI output voltage is approximately 3.3V. As the

cable

length

increases,

the

CLI

voltage

decreases

providing an approximate correlation between the CLI

voltage and cable length.

In applications where there are multiple input channels

using

the

GS1504,

it

is

advantageous

to

have

a

programmable mute output.

The output of the GS1504 can be muted when the input

signal decreases below a preselected input level. The

voltage applied to the MCLADJ pin vs input cable length is

shown in Figure 12. The MCLADJ pin may be left

unconnected for applications where output muting is not

required. This feature has been designed for use in

applications such as routers where signal crosstalk and

circuit noise cause the equalizer to output erroneous data

when no input signal is present. The use of a Carrier Detect

function with a fixed internal reference does not solve this

problem since the signal to noise ratio on the circuit board

3.5

3

2.5

2

1.5

1

0.5

0

0

50

100

150

200

CABLE LENGTH (m)

3.5

3

2.5

2

1.5

1

0.5

0

0

50

100

150

CABLE LENGTH (m)

50

50

SDO

SDO

+100mV

-100mV

typical

+100mV

-100mV

typical