AK4679: 24-bit Stereo CODEC Embeds Open-Core DSP for Audio and Voice Processing

AKM Semiconductor today introduced the AK4679, a highly integrated stereo CODEC and DSP featuring a dual PCM interface for mobile device applications, including smart phones and tablet computers. The AK4679 is the newest member in the Audio2go™ product family. It includes a stereo cap-less Class-G headphone amplifier, a class-D speaker amplifier, and a dual PCM interface that connects the stereo CODEC to a base band IC or Bluetooth IC for sound recording and playback. The PCM interface block includes an integrated sample rate converter that enables asynchronous mixing of audio and PCM data, making the AK4679 ideal for applications with a Bluetooth headset.

The AK4679 integrates a very low-power DSP that is effective for sound quality improvement of voice communications, music playback and audio recording functions. AKM’s proprietary royalty-free algorithms for voice communications, including a two-microphone noise suppressor and echo canceller, enable highly audible phone calls while minimizing noise. Clarity enhancement and bandwidth extension algorithms that improve both voice transmission and reception are available for porting to the AK4679. Supporting wideband signals, the AK4679 can be used for VoIP applications. In addition to voice functions, the DSP is highly effective for full-bandwidth music playback (audio processing), as well as a microphone zoom feature that synchronizes camera zoom to sound direction for video recordings.

The microphone input circuit includes a digital microphone interface for converting one-bit data (PDM) into 24-bit linear PCM data. The AK4679 has an integrated charge pump that generates an internal negative rail, enabling ground-referenced outputs for the cap-less headphone amplifier. This headphone amplifier eliminates large ac-coupling capacitors, achieving stable signal characteristics in low frequency bands, reducing cost and meeting space saving demands for portable devices. The ADC output and digital microphone input are automatically adjusted by an ALC circuit, and high quality audio recording can be realized using an internal five-band equalizer and a three-band dynamic range control circuit. The AK4679 is optimized for extremely low power operation: 5mW for recording (stereo) and 3.7mW for playback (headphone).

The AK4679 integrates a low noise analog stereo microphone preamplifier that supports either single-ended or differential input, a power supply circuit for an external microphone that supports two line output switching, an ALC circuit for either recording or playback, a 45mW stereo class-G headphone amplifier and a 1.57W mono class-D speaker amplifier. An integrated PLL generates all required audio clocks internally, ensuring simple interface to external processors. The PLL includes an internal loop filter, eliminating the traditional external filter circuit. Functions are controlled through a serial control I2C bus interface. The AK4679 supports sampling rates from 8kHz to 48kHz, and the operating voltage ranges from 1.1V to 1.3V for the DSP block, from 1.7V to 2.0V for the analog block, from 1.7V to 2.0V for the digital block, from 3.0V to 5.5V for the speaker amplifier, and from 1.6V to 3.6V for the digital interface block. It is housed in a space saving 78-pin FBGA package (4.5mm x 4.5mm).

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