Cirrus Logic AN306 - Manual (Page 3)

AN306REV1 3
AN306
5. LOCALIZED MASTER CLOCK RECOVERY AND DISTRIBUTION
The Recovered Master Clock (RMCK) output is a unique feature of the CS4350. The RMCK output allows the
CS4350’s high-speed recovered clock Master Clock signal to be used as the Master Clock for other more typical
audio converters that do not have built-in PLLs. This feature is useful for localizing the high-speed clock to a portion
of the circuit board separate from the rest of the system, or when the integrity of a long Master Clock run could affect
the converter performance.
Figure 3 shows the CS4350 receiving only the necessary PCM clocks from a distant source while generating a re-
covered Master Clock to be used locally to the CS4350. This allows the RMCK signal recovered and provided by
the CS4350 to be used in a small area, thereby easing the system design and the routing of clocks.
Some audio converters require specific MCLK to LRCK ratios that vary according to the sample rate. The CS4350’s
RMCK output can provide this ratio variance independently from its internal Master Clock signal. This allows flexi-
bility in the local audio converters that are using the CS4350’s RMCK output by providing a wider range of
MCLK/LRCK ratios for use.
For converters that have an automatic speed mode detection feature, no register writes are necessary to change
from 44.1 kHz to 96 kHz sample rates as the CS4350’s RMCK can be set to automatically adjust the MCLK to LRCK
ratio accordingly. See Section 4.2.1 of the CS4350 data sheet for more details on this feature.
PCM
Serial
Interface
Serial Data Input 1
Phase Locked
Loop
Left-Right Clock
Lo
ca
l Re
co
ve
re
d
M
C
L
K
Serial Clock
PCM
Serial
Interface
Serial Data Input 2
PCM
Serial
Interface
Serial Data Output
CS4350
PLL DAC
DAC
ADC
SDIN1
SCLK
RMCK
LRCK
SDIN2
SCLK
LRCK
MCLK
SDOUT
SCLK
LRCK
MCLK
Long Board Traces
DSP/SOC
Figure 3. Localized MCLK using CS4350 RMCK Output