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WM8742 Stereo D/A Converter with Advanced Digital Filters

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WM8742 Stereo D/A Converter with Advanced Digital Filters

Cirrus Logic's WM8742's selectable roll-off and performance characteristics provide benefits like reduced pre-ringing and minimal group delay

Cirrus Logic's WM8742 is a stereo digital/analog converter (DAC) that provides fine resolution volume, soft mute control, digital de-emphasis, and a range of advanced digital filter responses, followed by a digital interpolation filter, multi-bit delta-sigma modulator, and stereo DAC. The device optimizes the DAC linearity and provides maximum insensitivity to clock jitter. The digital filters include several selectable roll-off and performance characteristics. This flexibility provides a range of benefits, such as significantly reduced pre-ringing and minimal group delay. The WM8742 supports PCM data input from 16-bits to 32-bits and sampling rates up to 192 kHz, as well as DSD bit-stream data format in both direct DSD and PCM-converted DSD modes.

Block Diagram

Features
  • Excellent measured performance and advanced digital filters to optimize listener's desired audio profile
  • Several selectable roll-off responses (standard sharp or slow roll-off) and performance characteristics (non-half band filters and minimum phase filters)
  • User-selectable digital filters (5 for each PCM sampling rate, 4 for DSD Plus):
    • Ripple: measure of how much the filter will affect signals in the passband
    • Cut-off: frequency above/below (depending on filter type) which signal components will be significantly attenuated
    • Time smear: frequency signals pass through the filter at slightly different rates from one another
    • Phase response: linear phase filter may shift the phase of a signal by a large amount but will exhibit the same amount of phase shift for both high- and low-frequency signals
  • Filter characteristics continued
    • Latency: the delay as the signal passes through a filter; low latency filter might be necessary for time or synchronization-sensitive applications such as studio applications
    • Pre-ringing: output signal reproduced by the digital filter starts to change before it is intended to due to the feedback characteristics of the filter
    • Group delay distortion: changes per the input frequency of the signal
    • Apodizing effect: smooths discontinuities that can be introduced by sharp filter cut-offs and provides the ability to remove distortion introduced during the recording process
  • Flexibility provides a range of benefits, such as significantly reduced pre-ringing and minimal group delay; internal digital filters can be by-passed and the WM8742 can be used with an external digital filter
Direct and Plus DSD Support
  • Mono and stereo configurations
  • DSD Direct
    • True DSD mode
    • All internal filtering bypassed
    • Requires an external analog filter to remove high-frequency energy present in a DSD signal
  • DSD Plus
    • DSD input can be manipulated internally as if it were PCM
    • Advanced digital filters can be selected by the user to match requirements
    • Analog filter on output can be less aggressive, and lower order, than DSD Direct
  • Operates from 64 fs DSD clock – no MCLK input required

Applications

  • Professional recording systems
  • A/V receivers
  • High specification CD, DVD, and home theater systems