GS1574A Data Sheet
+187.5mV
V
= 2.925V
typical
CM
-187.5mV
SDO
SDO
+187.5mV
50
50
V
= 2.925V
typical
CM
-187.5mV
Figure 4-1: Typical Output Voltage Levels
4.3 Programmable Mute Output
For SMPTE 259M inputs, the GS1574A incorporates a programmable threshold
output mute (MCLADJ).
In applications where there are multiple input channels using the GS1574A, it is
advantageous to have a programmable mute output to avoid signal crosstalk.
The output of the GS1574A can be muted when the input signal decreases below
a certain input level. This threshold is determined using the input voltage applied
to the MCLADJ pin. 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 could be significantly less than the default signal detection level set by
the on chip reference.
NOTE: MCLADJ is only recommended for data rates up to 360Mb/s. For data rates
above this, MCLADJ should be left floating.
4.4 Mute and Carrier Detect
The GS1574A includes a MUTE input pin that allows the application interface to
mute the serial digital output at any time. Set the MUTE pin HIGH to mute SDO and
SDO. In this case, the outputs will mute regardless of the setting of the BYPASS pin.
A Carrier Detect output pin (CD) indicates the presence of a valid signal at the input
of the GS1574A. When CD is LOW, the device has detected a valid input on SDI
and SDI. When CD is HIGH, the device has not detected a valid input.
NOTE: CD will only detect loss of carrier for data rates greater than 19Mb/s. The
CD output pin may be connected directly to the MUTE input pin to enable automatic
muting of the GS1574A when no valid input signal has been detected.
NOTE: If the maximum cable length is exceeded and the device is not in bypass
mode the GS1574A will not assert the CD pin even if a carrier is present.
33416 - 5 March 2006
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GENNUM [ GENNUM CORPORATION ]
