WM8742GEDSSLASHRV datasheet(27/66 Pages) CIRRUS

27 / 66 page

WM8742

Rev 4.4

The following diagram illustrates timing for a daisy chain with 2 WM8742 devices.

Figure 21 Audio Interface Daisy Chaining Timing

DSD MODE

The WM8742 supports DSD input bitstreams at 64x the oversampling rate. The data is supplied at a

rate of 64 bits per normal word clock. In DSD, no word clock is provided.

The WM8742 supports two channels of bitstream or DSD audio. Data bitstreams and the 64fs clock

are supplied to pins 1, 22 and 3 respectively. The MODESEL[1:0] register bits control whether the

device operates in DSD direct, DSD plus or PCM modes.

DSD DIRECT

In DSD Direct mode the internal digital filters are bypassed, the input bitstream data is subjected to

the minimal possible processing and is applied directly to the switched capacitor stage of the DAC

system. Using this mode provides the purest possible representation of a DSD stream.

It is normally desirable to use an external analogue post-DAC analogue filter to combine the

differential outputs of the DAC and remove high frequency energy from the output. This is particularly

important in the case of DSD operation due to the presence of high frequency energy which is a result

of the aggressive high order noise shaping used in the creation of the modulated DSD datastream.

DSD PLUS MODE

In DSD Plus mode the DSD data can be filtered in a similar manner to the data in the PCM path. The

DSD Plus filters are selected using register bits DSDFILT[1:0]. DSD Plus mode is not available under

hardware control.

Although DSD Plus mode requires that the bitstream is more heavily processed than DSD Direct, the

advantage is that DSD Plus mode reduces the high frequency energy which is a result of the

aggressive high order noise shaping used in the creation of the modulated DSD datastream. This

means that a less aggressive, lower order, analogue filter can be used at the output. Furthermore the

slew-rate requirements of the op-amps can be relaxed compared to DSD direct mode, due to the

reduction in high frequency energy.

WM8742GEDS/RV 数据表(PDF) 27 Page - Cirrus Logic