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GaN Systems: All Eyes On Audio Amplifiers

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With the Class D audio amplifier market poised for massive growth, GaN Systems has set its sights on snaring a big chunk of the sector, reports Rebecca Pool.

When it comes to the wonderful world of audio, not all solid-state amplifiers are created equal. For decades, the analog-based linear amplification Class A audio system has reigned supreme, with audiophiles tolerating its very low efficiency.

Not anymore. Today, a growing number of power semiconductor suppliers are delivering a new breed of GaN-based Class D audio amplifier that promises far higher power efficiencies than your archetypical Class A amplifier.

For example, Infineon Technologies has developed its 'MERUS' class D audio amplifier ICs that are said to maximize power efficiency and dynamic range while providing stunning audio performance in small product form factors. And GaN Systems has recently released a Class D amplifier evaluation kit that also promises to deliver unprecedented efficiency and sound quality.

“When some of my very discerning customers from Japan first listened to our GaN amplifier, they told me that it was like arrows of sounds coming from the speaker,” says Rick Reigel, Vice President of Sales at GaN Systems. “On closing their eyes they said they could feel the music and it felt as if it were live, rather than an artificially reproduced sound - this is the kind of reaction that we get.”

Gathering momentum

Operating as electronic switches rather than linear gain devices, Class D amplifiers were initially developed in the 1950s. However, these systems didn't truly reach the market until the 1990s, with the advent of adequate-performing silicon MOSFETs.

Historically, these systems have been relegated to lower-quality audio systems as the use of silicon can lead to audio distortion arising from imperfect switching and high on-state resistance.

However, Reigel is confident that the new wave of GaN MOSFET-based amplifier systems will change this, offering sound quality as well as higher efficiencies.

“GaN is going to continue the curve of improvement and can deliver a smaller, lighter, more efficient amplifier,” he says. “The GaN MOSFET ensures much cleaner switching, enabling better linearity in the amplifier as well as less intermodulation distortion, which means [suppliers] can continue to shrink amplifier size without sacrificing sound quality, which is a trend we're seeing across the industry.”

“We can get a high-fidelity sound using GaN in this Class D topology, as well as this great blend of size, weight, efficiency and cost,” he adds. “This is the real value proposition of GaN in this application, and you just can't achieve it in any other way.”

GaN Systems evaluation kit

GaN Systems' recent evaluation kit includes a 2 channel, 200 W per channel class D audio amplifier and companion 400W continuous power audio-grade switched-mode power supply (SMPS) without heatsinks. A single GaN FET design is used for front-end power factor correction with a dual GaN FET half-bridge used for the back-end LLC SMPS.

Crucially, the set-up allows for a low-cost three FET design that doesn't demand a massive external heat-sink for full-power operation. And GaN Systems has also developed a low inductance GaN transistor package.

“In the pre-amplifier part of the design, we have a lot of silicon and this links to the audio source, say, a CD player or music files,” highlights Reigel. “If you want to drive a stereo application with the full bridge, then there's actually eight GaN transistors in the output stage, just prior to the speaker.”