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Codec reduces headphone 'pops and clicks'

Posted: 11 Dec 2009     Print Version  Bookmark and Share

Keywords:codec  line driver  Class W headphone  amplifier 

Low-power codec extends playback time in portable apps

WM8904 codec

Wolfson Microelectronics has released an ultra low-power codec with Class W headphone and line drivers, designed to offer low power consumption and extend playback time in portable applications, such as media players, headsets, voice recorders and multimedia phones.

The WM8904 is part of Wolfson's family of next-generation ultra low-power audio devices and claims to deliver high-performance audio and market-leading power consumption in an ultraslim, low-profile form factor.

Incorporated within the WM8904 is Wolfson's Class W amplifier technology, which intelligently tracks the actual music signal level and uses an adaptive dual drive charge pump to optimise power dissipation. The ground referenced output also eliminates the need for large DC blocking headphone capacitors, resulting in improved bass response, and savings in PCB space and the audio sub-system BOM.

Also featuring in the WM8904 is Wolfson's innovative SmartDAC technology, a low power DAC capacitor switching architecture, which enables DAC to headphone power consumption of 4mW and delivers up to 30mW per channel into a headphone load.

Audio performance is enhanced with the integration of Wolfson's SilentSwitch technology, which extends its 'pop and click' suppression capability by incorporating sophisticated clamp and sequencer circuitry. With this feature, unwanted noise at the headphone and line outputs is reduced during power-up/down and mute/un-mute by clamping the output to ground. Using an integrated control write sequencer with programmable delay times to power-up and power-down parts of the WM8904 further reduces 'pops and clicks', as well as reducing time to market by lowering software driver development time.

In addition, the WM8904 incorporates an advanced Dynamic Range Controller (DRC), which enhances audio performance. When in record mode the DRC can be flexibly configured to optimise recorded sound quality, preventing distortion whilst maximising the recorded signal. Wolfson has also implemented a 'quick release' feature that enhances the intelligibility of recorded sound in the presence of loud impulse noises. This feature ensures that noisy events such as user handling do not mask the recorded signal. In playback mode, the DRC maximises the volume of the output signal, boosting the perceived loudness of the audio data.

Wolfson's ReTune Mobile parametric equaliser is a feature which enables system designers to accurately customise the output signal path to optimise the performance of the speaker or other transducer. Line inputs, along with digital and analogue microphone inputs, are all supported, with bypass paths to the class W headphone and line outputs.

The WM8904 is available in two compact package options including an ultra-small 2.6mm x 2.5mm CSP.

The WM8904 is available for sampling now in a 32-lead 4mm x 4mm QFN, 36-ball CSP package.

WM8904 customer evaluation boards with the Wolfson Interactive Setup and Configuration Environment (WISCE) are available to aid device evaluation and development. WISCE connects to the evaluation board over USB and offers an interactive register map interface.

- Paul Buckley
Analog Designline Europe

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