PCM1808
www.ti.com
SLES177A–APRIL 2006–REVISED AUGUST 2006
SYNCHRONIZATION WITH DIGITAL AUDIO SYSTEM
In slave mode, the PCM1808 operates under LRCK (pin 7), synchronized with system clock SCKI (pin 6). The
PCM1808 does not require a specific phase relationship between LRCK and SCKI, but does require the
synchronization of LRCK and SCKI.
If the relationship between LRCK and SCKI changes more than ±6 BCKs for 64 BCK/frame (±5 BCKs for 48
BCK/frame) during one sample period due to LRCK or SCKI jitter, internal operation of the ADC halts within 1/fS
and digital output is forced to zero data (BPZ code) until resynchronization between LRCK and SCKI is
established.
In the case of changes less than ±5 BCKs for 64 BCK/frame (±4 BCKs for 48 BCK/frame), resynchronization
does not occur and the previously described digital output control and discontinuity do not occur.
Figure 25 illustrates the digital output response for loss of synchronization and resynchronization. During
undefined data, the PCM1808 can generate some noise in the audio signal. Also, the transition of normal data to
undefined data creates a discontinuity in the digital output data, which can generate some noise in the audio
signal. The digital output is valid after resynchronization completes and the time of 32/fS has elapsed. Because
the fade-in operation is performed, it takes additional time of 48/fin or 48/fS until the level corresponding to the
analog input signal is obtained. If synchronization is lost during the fade-in or fade-out operation, the operation
stops and DOUT (pin 9) is forced to zero data immediately. The fade-in operation resumes from mute after the
time of 32/fS following resynchronization.
Resynchronization
Resynchronization
Synchronization Lost
Synchronization Lost
State of
Synchronization
Synchronous
Asynchronous
Synchronous
32/f
S
Asynchronous
Synchronous
1/f
S
Undefined
Data
DOUT
Normal Data
Zero Data
Normal Data
Zero Data
Normal Data
Fade-In Complete
Fade-In Start
Fade-In Restart
Normal Data
DOUT
BPZ
(Contents)
32/f
S
48/f or 48/f
48/f or 48/f
in S
in
S
T0082-01
Figure 25. ADC Digital Output for Loss of Synchronization and Resynchronization
18
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