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6.5 Word Clock Input and Output
Input
The ADI-8 PRO's word clock input is active, when EXT is chosen in the clock section (see
chapter 7, Clock Section). As soon as a valid signal is detected, the EXT LED is constantly lit,
otherwise it is flashing slowly.
Thanks to RME's Signal Adaptation Circuit, the word clock input still works correctly even with
heavily mis-shaped, dc-prone, too small or overshoot-prone signals. Thanks to automatic signal
centering, 300 mV (0.3V) input level are sufficient in principle. An additional hysteresis reduces
sensitivity to 1.0 V, so that over- and undershoots and high frequency disturbances don't cause
a wrong trigger.
The ADI-8 PRO's word clock input is shipped as
high impedance type (not terminated). A push switch
allows to activate internal termination (75 Ohms).
The switch is found on the back next to the BNC jack.
Use a small pencil or similar and carefully push the
blue switch so that it snaps into its lock position.
Another push will release it again and de-activate the
termination.
Output
The word clock output is constantly active and basically delivers the sample rate of the AD-
converter. As long as it is working with internal clock, the output word clock is extremely stable
and jitter-free (< 1 ns). The device can even be used as a central word clock generator (except
for the limitation of having only one output). In slave mode (EXT/INPUT), the amount of jitter is
depending on the input signal.
A word clock signal fed to the ADI-8 PRO can even be passed through via the word clock
output, because the output signal is phase locked to the input signal (0°). Thus the usual T-
adaptor at the input is not needed, and the ADI-8 PRO can be used as a signal refresher.
This application is even more interesting, because the exceptional input of the ADI-8 PRO
(1 Vss sensitivity instead of the usual 2.5 Vss, dc cut, Signal Adaptation Circuit) guarantees a
secure function also with critical word clock signals.
Thanks to a low impedance, but short circuit proof output, the ADI-8 PRO delivers 4 Vss to
75 Ohms. For wrong termination with 2 x 75 Ohms (37.5 Ohms), there are still 3.3 Vss at the
output.
User's Guide ADI-8 PRO © RME
11
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