Wolfson Microelectronics has introduced a stereo audio Codec for multimedia mobile phones and similar applications. The WM8983 enables flexible usage modes for mobile phones. These include initiating normal mobile phone functions while continuing to listen to MP3 or FM radio, as well as audio playback during calls. Other modes include karaoke during voice calls, with full mixing capability for headphone playback as well as recording in I2S format.
The device includes a dedicated input and output audio mixer with audio loopback for hi-fi recording, 2 microphone amplifiers, and output drivers for speaker, headphones and differential or stereo line outputs. This eliminates separate speaker and headphone amplifiers, enabling a lower component count and a reduced footprint implementation. The high-output BTL speaker driver is capable of driving 1 Watt into 8 ohm BTL speaker, while the headphone driver supports “capless” operation enabling further space and cost savings.
Wolfson’s mixed-signal technology also enables digital signal processing on-chip, enabling new mobile devices to add innovative features exploiting hi-fi quality audio. By integrating a 5-band equalizer, 3D audio enhancement, automatic level control and record limiter, the on-chip DSP is able to reduce the MIPS demand on the device’s main multimedia processor, for enhanced performance and lower overall power consumption. These DSP features enable a mobile phone to play MP3 music or MPEG4 movies with only the multimedia processor and audio Codec turned on, achieving power savings which can lead to longer battery life. The WM8983 digital audio interface can operate in master or slave mode, while an integrated PLL supports flexible clocking schemes. A-law and µ-law companding are fully supported.
A digital wind noise filter is also implemented, as well as an IIR filter that is programmable as a notch filter. This enables fixed frequency noise reduction for improved voice and audio performance. There is also additional power-up and power circuitry to reduce audible pops and clicks. Digital to analog converter (DAC) performance is 98 dB SNR and –84 dB THD, while performance of the analogue to digital converter (ADC) is 95 dB SNR and –84 dB THD. The WM8983 operates at analog supply voltages from 2.5V to 3.3V, although the digital core can operate at voltages down to 1.71V to save power. Speaker supplies can operate up to 5V for increased speaker output power. Additional power management control enables individual sections of the chip to be powered down under software control.
