3.5
3
2.5
2
1.5
1
0.5
0
0
50
100
150
200
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
50Ω as shown in Figure 21.
+100mV
V
CM
= 4.0V
typical
SDO
-100mV
CLI VOLTAGE (V)
GS1504
CABLE LENGTH (m)
Fig. 19 CLI Voltage vs. Belden 1694A Cable Length
3.5
3
CLI VOLTAGE (V)
SDO
2.5
2
1.5
1
0.5
0
0
50
100
150
+100mV
50
50
V
CM
= 4.0V
typical
-100mV
Fig. 21 Typical Output Voltage Levels
CABLE LENGTH INDICATION/CARRIER DETECT/MUTE
CABLE LENGTH (m)
Fig. 20 CLI Voltage vs. Belden 8281 Cable Length
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
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
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