Wolfson Microelectronics has announced the WM8991 audio CODEC featuring a dual mode, 1W speaker driver with the flexibility to switch between Class AB and Class D operation. The WM8991 is based on Wolfson’s ‘Audio Hub’ concept which is enabling multi-media handsets which can mix and select from multiple audio sources including voice, radio, music, mobile TV and Wi-Fi. Offered in 5mm x 5mm BGA packaging and with 98dB SNR performance, the WM8991 supports the signal switching, audio conversion and voice mixing requirements for mobile phones, allowing designers to add new features and enabling flexible new end-user modes such as viewing TV during a voice call. The digital core can be as low as 5mW during a voice call. The ability to select Class AB or Class D operation allows handset designers to deploy filterless Class D technology into a wider range of increasingly diverse handheld form factors where restrictions such as noise and interference previously demanded a Class AB driver topology. System designers may select the most appropriate mode of operation for the anticipated usage scenario, allowing battery life for the end user to be maximised.

Eight analogue inputs and nine pop-free analogue outputs eliminate the need for external input or output switches. This means that designers can integrate a second processor, such as the digital TV tuner, without tri-stating the main processor interface. All line-in and line-out ports are fully balanced and feature differential signalling, allowing high-speed cellular handsets to deliver high performance, noise-free audio. General Purpose IOs permit designers to implement button or accessory detect with programmable button debounce to support handset differentiating features, as well as added-value capabilities such as processor wake-up from low-power sleep mode. There is also a dedicated MIC BIAS input pin supporting eight programmable current detect levels for enhanced accessory support.

The WM8991 features a fully differential headphone output, which eliminates external capacitors to save more space and minimise the bill of materials, reduce noise and crosstalk and improve bass quality. Phantom ground design, as well as the provision of an AC coupled mode, allows the headphone output to drive an additional ear speaker. Advanced voice features include digital sidetone, allowing low frequency noise, such as wind noise and mechanical vibration, to be digitally filtered from the attenuated voice feedback signal.