WM8904: Ultra low power CODEC for portable audio applications


The WM8904 is a high performance ultra-low power stereo CODEC optimised for portable audio applications.

The device features stereo ground-referenced headphone amplifiers using the Wolfson ‘Class-W’ amplifier techniques - incorporating an innovative dual-mode charge pump architecture - to optimise efficiency and power consumption during playback. The ground-referenced headphone and line outputs eliminate AC coupling capacitors, and both outputs include common mode feedback paths to reject ground noise.

Control sequences for audio path setup can be pre-loaded and executed by an integrated control write sequencer to reduce software driver development and minimise pops and clicks via Wolfson’s SilentSwitch™ technology.

The analogue input stage can be configured for single ended, or differential  inputs. Up to 3 stereo microphone or line inputs may be connected. The input impedance is constant with PGA gain setting.

A stereo digital microphone interface is provided, with a choice of two inputs.

A dynamic range controller provides compression and level control to support a wide range of portable recording applications. Anti-clip and quick release features offer excellent performance in the presence of loud impulsive noises.

ReTune™ Mobile 5-band parametric equaliser with fully programmable coefficients is integrated for optimization of speaker characteristics. Programmable dynamic range control is also available for maximizing loudness, protecting speakers from clipping and preventing premature shutdown due to battery droop.

Common audio sampling frequencies are supported from a wide range of external clocks, either directly or generated via the FLL.

The WM8904 can operate directly from a single 1.8V switched supply. For optimal power consumption, the digital core can be operated from a 1.0V supply.


  • 3.0mW quiescent power consumption for DAC to headphone playback
  • 2.4mW quiescent power consumption for analogue bypass playback
  • DAC SNR 96dB typical, THD -86dB typical
  • ADC SNR 91dB typical, THD -80dB typical
  • Control write sequencer for pop minimised start-up and shutdown
  •  Single register write for default start-up sequence
  • Integrated FLL provides all necessary clocks
    - Self-clocking modes allow processor to sleep
    - All standard sample rates from 8kHz to 96kHz
  • Stereo digital microphone input
  •  3 single ended inputs per stereo channel
  • 1 fully differential mic / line input per stereo channel
  • Digital Dynamic Range Controller (compressor / limiter)
  • Digital sidetone mixing
  • Ground-referenced headphone driver
  • Ground-referenced line outputs
  • 32-pin QFN package (4x4mm, 0.4mm pitch)
  • 36-ball W-CSP package (6×6 ball grid, 0.4mm pitch)