Codec integrates Class-D speaker driver

Edinburgh, Scotland — Wolfson Microelectronics plc today rolled out an integrated codec with a filterless Class-D stereo speaker driver that is said to consume 10 milliwatts in playback mode.

The WM8960 codec also integrates stereo analog-to-digital (A/D) converters, digital-to-analog (D/A) converters, a headphone driver and an internal phase-locked loop (PLL).

The codec is intended for use in portable electronic devices such as mobile phones with stereo speakers and personal video players that require high-quality audio performance with high efficiency to extend battery life, said Yan Goh, Wolfson's product marketing manager.

The WM8960's Class-D speaker driver delivers up to 1-W continuously, offering 1 percent total harmonic distortion (THD) into 8 ohms, and features synchronous clocking with the D/A converter for low noise and pop and click suppression. The codec also includes a capless headphone driver mode, removing the need for bulky external components, according to Goh.

The highly flexible input configuration of the WM8960 includes a complete stereo single-ended or pseudo-differential microphone interface and up to three stereo analog sources to eliminate external analog switches, Goh said.

The WM8960 is available now in a 5 x 5-mm QFN package and is priced at $2.98 in 10,000-piece quantities. Click here for the WM8960 data sheet.

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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 WM8985 — a codec that is dynamically switchable between Class AB and Class D.

Today, Wolfson is following up with the WM8960 codec — its first 24-bit codec that integrates a filterless Class-D speaker driver. The company will be showcasing the WM8960 codec this week at the 3GSM Show in Barcelona.

Wolfson offers a variety of audio codecs targeting portable applications like MP3 players and cell phones. 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 x 5-mm 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 vice president of marketing.

The audio codec can digitize and replay audio signals with 97 dB 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 1-W speaker driver. It's unusual to see a 1-W speaker driver integrated into such a high quality audio codec, Hayes said The 1-W speaker driver is very efficient — it 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 synchronising 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 (1/2 watt versus 1 W), Hayes said. “We are now able to offer twice the output — with roughly one third the overall power consumption when playing back music,” he said.

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