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SLES100 − DECEMBER 2003
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 PCM1796.
The PCM1796 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 39. The word clock (WDCK) signal must be operated at 8× or 4× the desired sampling frequency, f .
S
Pin Assignment When Using the External Digital Filter Interface
D LRCK (pin 4): WDCK as word clock input
D BCK (pin 6):
Bit clock for audio data
D DATA (pin 5): Monaural audio data input when the DFMS bit is not set to 1
D ZEROL (pin 1): DATAL as L-channel audio data input when the DFMS bit is set to 1
D ZEROR (pin 2): DATAR as R-channel audio data input when the DFMS bit is set to 1
38
BB [ BURR-BROWN CORPORATION ]
