Carrier Detect function with a fixed internal reference
because the signal to noise ratio on the circuit board may
be significantly less than the default signal detection level
set by the on- chip reference. To solve this problem, the
GS9024C provides a user adjustable threshold to meet the
unique conditions that exist in each user's application.
Override and internal default settings are provided to give
the user total flexibility.
4. OUTPUT EYE MONITOR
5.2. High Speed Outputs (SDO/SDO)
SDO/SDO are current mode outputs that require external
pullups (see Figure 12). The output signal swings are
800mV when 75Ω resistors are used. A diode can be
placed between V
CC
and the pullups to shift the signal
levels down by approximately 0.7 volts. When the output
traces are longer than 1 inch, controlled impedance traces
should be used. The pullup resistors should be placed at
the end of the output traces as they terminate the trace in
its characteristic impedance (75Ω).
GS9024C
The GS9024C provides an 'Output Eye Monitor' (OEM)
which allows the verification of signal integrity after
equalization, prior to reslicing. The OEM pin is an open
collector current output that requires an external 50Ω pullup
resistor. When the pullup resistor is not used, the OEM
block is disabled and the internal OEM circuit is powered
down. The OEM provides a 0.25V
p-p
signal when driving a
50Ω oscilloscope input.
5. I/O DESCRIPTION
5.1. High Speed Analog Inputs (SDI/SDI)
GS9024C
SDO
SDO
V
CC
75Ω
75Ω
Fig. 12
SDI/SDI are high impedance inputs
differential or single-ended input drive.
which
accept
Figure 11 shows the recommended interface when a single-
ended serial digital signal is used.
10nF
75Ω
75Ω
10nF
SDI
37.5Ω 75Ω
SDI
GS9024C
APPLICATIONS INFORMATION
The Typical Application Circuit shown on page 8 is useful
for both SMPTE and DVB-ASI signals. The two AGC
capacitors shown however increase the AGC time constant
from the original times shown in earlier SMPTE-only
application circuits. In this case a minimum off-time of 50ms
is needed when break-before-make switching is used at the
input in order for the AGC voltage to recover.
Fig. 11
7
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