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Dual-mode audio CODEC can drive Class AB or D stages

San Diego, Calif.&#8212Wolfson Microelectronics' WM8991 lays claim to the industry's first mobile audio CODEC with a switchable driver stage that can be operated in Class AB or D for an 8-ohm speaker.

Thus the chip allows handset designers to deploy filterless Class D technology, where restrictions such as noise and interference previously demanded a Class AB driver topology. Eight analog inputs and nine “pop-free” analog outputs eliminate the need for external input or output switches. Designers can quickly integrate a second processor, such as the digital TV tuner without need for a tri-state interface to the main processor. Line-in and line-out ports are fully balanced and feature differential signalling.

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The chip also includes general purpose I/Os, which permit designers to implement “button” or “accessory detect” functions with programmable button debounce to support handset features. These I/Os also enable value-added capabilities such as processor wake-up from a low-power sleep mode. A dedicated microphone input pin supports eight programmable current-detect levels for enhanced accessory support.

The WM8991 also includes fully differential headphone drivers (40 mW into 16 ohms at 3.3 volts), which eliminates external capacitors to save space and lower the bill of materials, reduce noise and crosstalk, and improve bass quality. The chip's “phantom ground” design, as well as provision for an AC coupled mode allows the headphone output to drive an ear speaker.

Advanced voice features include digital sidetone, which facilitates digital filtering from the attenuated voice-feedback signal, thus minimizing low-frequency noise (such as due to the wind and mechanical vibration).

The WM8991 is available in sampling now. Click here to access the product datasheet. The WM8991, in a 5-by-5 mm BGA package, is priced at $2.68 each in 10k pieces.

Wolfson Microelectronics, Inc. , 1-858-676-5090, www.wolfsonmicro.com

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