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PWM controller provides digital integration for consumer audio designs

San Diego, US and Edinburgh, UK — January 12, 2004 — Wolfson Microelectronics plc today introduced the WM8608, the first of a family of feature-rich class D devices. The WM8608 is capable of providing up to 7.1 channels of pulse-width modulation (PWM) output from four stereo PCM inputs. This product marks a new entry for Wolfson in the Class D technology field and is the result of a significant development project.

The WM8608 comprises a high-performance multi-channel PWM digital power amplifier controller. Six identical full audio bandwidth channels, plus a reduced bandwidth sub channel are provided as PWM outputs. PWM outputs are selectable as either CMOS or LVDS, the latter being advantageous in helping reduce EMI and potential radio interference and allow greater flexibility in PCB layout, as tracking can be longer. By simply adding appropriate power output stages a multi-channel power amplifier may be built.

Class D, or switch-mode amplifiers, are rapidly replacing linear amplifiers in audio systems, especially in portable, power-sensitive CD and DVD players, providing an acceptable balance between power usage and distortion. Class D devices replace multiple digital to audio converters, increase power efficiency in battery-powered devices and offer reduced costs to final products.

Supporting up to 7.1 audio input channels in PCM format, these may be mixed down to 6.1 or 5.1 outputs, by mixing rear channel data into centre rear or surround speakers if required. If 5.1 channel data is input, the surround data may be processed internally to create a pseudo 6.1 signal with rear channel output. In the digital domain a 4-band Graphic Equaliser function is provided, selectable high frequency equalisation to suit different speaker types and independent volume control for each channel (+24dB to -103.5dB in 0.5dB steps).

The DSP architecture utilises a dynamic peak compressor for each channel which prevents digital clipping when gains of greater than 0db are applied and to ensure adequate signal amplitude to allow headroom for graphic equalisation. System clocking in simplified by utilising the onboard PLL which not only enables the device to run off MPEG and audio clocks but enhances performance within the system.

The WM8608 may be used with integrated power stages from vendors such as TI or ST or with a suitable pre driver and discrete FETs (e.g. Zetex, Vishay, Fairchild). Typical performance using an integrated power stage has given 96dB SNR, 0.1% THD at 30W.

The WM8608 is available in a TQFP-48 operating on 2.7V to 3.6V supplies. It is available now along with evaluation platforms for a 6.1 channel system and is currently priced at $4.17 (U.S.) in quantities of 10,000.

For more information contact Wolfson Microelectronics plc, Bernard Terrace, Edinburgh, EH8 9NX, United Kingdom, Tel: +44 (0) 131 272 7000, Fax: +44 (0) 131 272 7001

Wolfson Microelectronics

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