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Electronic Design

Stereo Codec Includes Integrated Headphone Driver

Designed for portable MP3 players and recorders, the WM8731 is Wolfson Microelectronics' new-est low-power stereo codec. It comes with an integrated headphone driver and provides programmable sample rates from a single clock source. Also, it generates all the audio sample-rate clocks from a single 12-MHz source. Master or slave clocking modes are offered as well.

The patent for this novel clock-generation technology is pending. Designers can independently program the 24-bit stereo codec's multibit delta-sigma analog-to-digital and digital-to-analog converters (ADCs and DACs) for sampling rates from 8 to 96 kHz. The selectable ADC high-pass filter is used to remove the residual dc offset. And, the digital audio input word lengths can vary from 16 to 32 bits.

The ADC's signal-to-noise ratio (SNR) is 97 dB at a 48-kHz sampling rate (A-weighted), while the codec's DAC part offers 100-dB SNR at the same sampling frequency (A-weighted). The on-chip 2- or 3-wire serial control interface provides access to volume controls, mutes, de-emphasis, and power-management features. For driving headphones from a programmable volume control, the stereo audio outputs are buffered. Typical output power from the headphone driver is 40 mW into a 16-Ω load. The headphone provides line-level outputs, along with antithump mute and power-up/down circuitry.

Fabricated in a 0.35-µm triple-metal double polysilicon CMOS process, the WM8731 consumes less than 18 mW in the playback mode. It also boasts a power-down mode, wherein the ADCs and DACs are bypassed to keep power consumption below 9 mW. While the digital supply range is 1.42 to 3.6 V, the analog supply range is 2.7 to 3.6 V. Packaged in a 28-pin SSOP, the WM8731 costs $3.16 each in 10,000-unit quantities.

Wolfson Microelectronics Ltd., 11 N. Market St., Ste. 670, San Jose, CA 95113; (408) 279-2882; fax (250) 764-4186.
Lutton Court, Bernard Terrace, Edinburgh EH8 9NX, the U.K.; +44 (0) 131 667 9386; fax +44 (0) 131 667 9386.

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