RF energy/heating applications boosted by 300W GaN transistor
The applications that MACOM cites include; a new generation of domestic and commercial microwave ovens in which a GaN-based PA replaces the magnetron; light-emitting-plasma-based lighting; automotive ignition; a range of drying and curing processes in industry and even domestically, with the ubiquitous laundry drying a possible market; medical applications such as tumour ablation (targeted delivery of heat), tissue warming, and sterilisation by heat.
Where RF energy has been generated by solid-state amplifiers, the prior technology has been LDMOS silicon: GaN has been seen, MACOM explains, as too expensive because it has been based on GaN on silicon carbide substrates. (GaN devices are invariably fabricated in an epitaxial layer of GaN grown on a carrier substrate: in earlier generation, SiC was technically easier. Silicon is much cheaper in that role, not least because larger wafer sizes are possible, allowing the normal learning curves of semiconductor production, moving to 150 mm then 200 mm wafers, to be applied.) MACOM has produced its current generation of parts not only using GaN-on-silicon, but moving to a moulded (plastic) package. There are four devices in this release, at 50, 100, 200 and 300W output; each offers gain of 17dB and efficiency of over 70%. The efficiency figure is a ‘true’ measure of DC-in to RF power out.
Using the 300W part, MACOM has also produced a PA module, a fully-assembled substrate of about 50 x 100 mm, for incorporation into a final product. In many cases – for example, manufacture of domestic microwave ovens for example – the appliance designers will have little experience of semiconductor amplifiers, or of routing RF power on PCBs: so a drop-in solution will be required. 300W out of a gain block with 17-dB added still requires significant drive, and MACOM has also produced an integrated module (above) with the complete RF path, and a digital control interface. The company expects to take these products, also, along a familiar electronics integration/shrink/cost reduction path.
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Mark Murphy, Senior Director of Marketing at MACOM explains some of the areas in which he expects RF energy delivery to proliferate. In lighting, an RF amplifier will energise a plasma in a sealed quartz bulb (the bulb sits at the focus of a standing wave in a resonant cavity). These lights are bright, efficient and have very good CRI (colour rendering index): they will appear in retail lighting, high-bay lighting and growing (greenhouse cropping) applications, among others. In automotive ignition, a controlled, plasma discharge as opposed to a discrete spark can improve fuel efficiency. In ovens and other heating applications, multiple RF sources can either be combined into a single higher-power feed, or can be focussed individually on to the target, allowing the use of phased-array, directed-energy designs. In all the potential applications, common factors are the ability to tune frequency and power, and to precisely control power levels, instantaneously, which has not been feasible with magnetron-based sources. Improved control will deliver benefits that include significant total energy savings, especially for high-power processes. As MACOM puts it, “The RF devices that underpin these [new] systems must strike an optimal balance of performance, power efficiency, small size, and reliability, at a price point that promotes mainstream commercial adoption.”
Providing 300W output power and 70% efficiency at 2.45GHz, the MAGe-102425-300 meets the core technical requirements for next generation power amplifiers proposed by the RF Energy Alliance, a non-profit technical association dedicated to unlocking the full potential of RF energy. Meanwhile the cost structure and volume supply chain benefits achieved with MACOM’s Gen4 GaN technology position the MAGe-102425-300 to meet aggressive cost targets on a par with LDMOS.
“Solid-state RF energy technology holds the promise to transform entire market segments, providing wide-ranging benefits from consumer goods to ISM systems and infrastructure,” said Mark Murphy, Senior Director of Marketing, MACOM. “The MAGe-102425-300 … signals a clear inflection point in the evolution toward mainstream RF energy adoption.”
“The RF Energy Alliance recently published the RF Power Amplifier Roadmap, which sets parameters for future PA module generations that are viable alternatives to magnetron-based solutions,” said Klaus Werner, Executive Director of the RF Energy Alliance. “The MAGe-102425-300’s breakthrough in efficiency is in step with our PA Roadmap, enabling new markets for residential solid-state RF energy applications.”
MACOM; www.macom.com/rfenergy
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