User's Guide ADI-648 © RME
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12.3 SteadyClock
The SteadyClock technology of the ADI-648 guarantees an excellent performance in all clock
modes. Its highly efficient jitter suppression refreshes and cleans up any clock signal, and pro-
vides it as reference clock at the word clock output.
Usually a clock section consists of an analog PLL for external synchronization and several
quartz oscillators for internal synchronisation. SteadyClock requires only one quartz, using a
frequency not equalling digital audio. Latest circuit designs like hi-speed digital synthesizer,
digital PLL, 200 MHz sample rate and analog filtering allow RME to realize a completely newly
developed clock technology, right within the FPGA at lowest costs. The clock's performance
exceeds even professional expectations. Despite its remarkable features, SteadyClock reacts
quite fast compared to other techniques. It locks in fractions of a second to the input signal,
follows even extreme varipitch changes with phase accuracy, and locks directly within a range
of 25 kHz up to 100 kHz.
SteadyClock has originally been de-
veloped to gain a stable and clean
clock from the heavily jittery MADI
data signal. The embedded MADI
clock suffers from about 80 ns jitter,
caused by the time resolution of 125
MHz within the format. Common jitter
values for other devices are 5 ns,
while a very good clock will have less
than 2 ns.
The picture to the right shows the
MADI input signal with 80 ns of jitter
(top graph, yellow). Thanks to
SteadyClock this signal turns into a
clock with less than 2 ns jitter (lower
graph, blue).
Using the other inputs sources of the
ADI-648, word clock and ADAT, you'll
most probably never experience such
high jitter values. But SteadyClock is
not only ready for them, it would han-
dle them just on the fly.
The screnshot to the right shows an
extremely jittery word clock signal of
about 50 ns jitter (top graph, yellow).
Again SteadyClock provides an ex-
treme clean-up. The filtered clock
shows less than 2 ns jitter (lower
graph, blue).
The cleaned and jitter-freed signal can be used as reference clock for any application, without
any problem. The signal processed by SteadyClock is of course not only used internally, but
also available at the ADI-648's word clock output. It is also used to clock the digital outputs.
