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Codec integrates Class-D speaker driver

Posted: 15 Feb 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Bettyann Liotta? Wolfson? WM8985? codec? WM8960?

Expect to see an avalanche of new devices coming out of Wolfson over the next few months. The company kicked off the latest product wave at the Consumer Electronics Show in January with the WM8985a codec that is dynamically switchable between Class AB and Class D.

Today, Wolfson is following up with the WM8960 codecits first 24bit codec that integrates a filterless Class-D speaker driver.

Wolfson offers a variety of audio codecs targeting portable applications like MP3 players and cellphones. Two key performance specs for codec customers are size and power consumption.

Simultaneously, consumers are demanding more features (like MP3 players that play both audio and video, phones with cameras, devices that support ringtones, etc.), which typically requires more power.

However, Wolfson's latest codec offers more features and lower power consumption. "This product, which is offered in the same size package (5-by-5mm QFN package) as Wolfson's older WM8750 codec, provides additional features but at the same time dramatically reduces power consumption," said Julian Hayes, Wolfson's VP of marketing.

The audio codec can digitize and replay audio signals with 97dB signal-to-noise ratio (SNR). In addition to expecting more features in portable applications, consumers want the same audio quality in their cell phone with a form factor not much larger than their standalone MP3 player, which this codec can accommodate, according to Hayes.

Another important aspect of this codec is its integrated, highly flexible input configuration. This codec has the ability to switch to three different audio signals/sources, Hayes said.

The most significant characteristic of the WM8960 codec, however, is the fact that it integrates a stereo 1W speaker driver. It's unusual to see a 1W speaker driver integrated into such a high quality audio codec, Hayes said The 1W speaker driver is very efficientit reduces the power it consumes when it's driving the speaker differentially, he said.

Maintaining high audio quality using a Class-D driver is no doubt a challenge, but that's how Wolfson is able to deliver low power consumption. Class AB devices typically consume more power than they deliver to the load, while Class-D consumes far less power, but produces more noise when switching. Wolfson takes care of this by carefully synchronizing the signal chain to the switching frequency of the Class D buffer.

Previously, Wolfson's older WM8750 codec utilized a mono Class AB speaker driver. The WM8750 and WM8960 are close in terms of performance, but the WM8750 only provided half the peak speaker output (0.5W versus 1 W), Hayes said. "We are now able to offer twice the outputwith roughly one third the overall power consumption when playing back music," he said.

- Bettyann Liotta

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