Datasheet

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SLES105B − FEBRUARY 2004 − REVISED NOVEMBER 2006
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39
Application for Interfacing With an External Digital Filter
For some applications, it may be desirable to use an external digital filter to perform the interpolation function,
as it can provide improved stop-band attenuation when compared to the internal digital filter of the PCM1792A.
The PCM1792A supports several external digital filters, including:
D Texas Instruments DF1704 and DF1706
D Pacific Microsonics PMD200 HDCD filter/decoder IC
D Programmable digital signal processors
The external digital filter application mode is accessed by programming the following bits in the corresponding
control register:
D DFTH = 1 (register 20)
The pins used to provide the serial interface for the external digital filter are shown in the connection diagram
of Figure 40. The word (WDCK) signal must be operated at 8× or 4× the desired sampling frequency, f
S
.
System Clock (SCK) and Interface Timing
The PCM1792A in an application using an external digital filter requires the synchronization of WDCK and the
system clock. The system clock is phase-free with respect to WDCK. Interface timing among WDCK, BCK,
DATAL, and DATAR is shown in Figure 42.
Audio Format
The PCM1792A in the external digital filter interface mode supports right-justified audio formats including 16-bit,
20-bit, and 24-bit audio data, as shown in Figure 41. The audio format is selected by the FMT[2:0] bits of control
register 18.
MSB LSB
16
BCK
DATA
1/4 f
S
or 1/8 f
S
DATA
DATA
WDCK
Audio Data Word = 16-Bit
Audio Data Word = 20-Bit
Audio Data Word = 24-Bit
1 2 3 4 5 6 7 8 9 10 11 12 13 14 151615
MSB LSB
161 2 3 4 5 6 7 8 9 10 11 12 13 14 152019 2017 18 19
MSB LSB
161 2 3 4 5 6 7 8 9 10 11 12 13 14 152423 2017 18 19 2421 22 23
Figure 41. Audio Data Input Format for External Digital Filter (Internal DF Bypass Mode) Application