TriQuint’s New PowerBand™ Technology Sets an Aggressive New Standard for Wideband, High Power Efficiency
By Mike Lincoln, Product Marketing Manager, and Mark Andrews, Marketing Communications Manager, TriQuint Semiconductor, Inc.

New technological and cost reduction mandates in military and public safety communication systems, as well as laboratory and production test amplifiers, specific radar systems and signal jamming equipment, require greater performance, better cost structures, and smaller, lighter form factors for wideband RF amplifiers.

RF circuit designers have struggled to develop multi-octave amplifiers that are efficient and conform to size and weight constraints while meeting cost targets. There are many technical hurdles affecting and often limiting broadband amplifier progression; the RF power transistor is a major factor that can limit performance - until now. TriQuint’s new PowerBand™ family of RF transistors offers high-efficiency operation across exceptional bandwidth – from 500 MHz to as much as 3 GHz. This advancement represents a leap in performance and size advantages, offering solutions to challenges that typically vex today’s broadband circuit designer.

Coping with Device Options in Broadband Design
Today’s typical RF power transistors are internally matched. This internal matching improves performance at a specific and narrow frequency band by moving the matching network closer to the active semiconductor die. This is an excellent solution for the narrowband RF amplifier designer. However, internally matched transistors are not an ideal solution for broadband amplifier designs because the performance of the device degrades rapidly as bandwidth expands.

Some wideband designs rely on high power discrete transistors with no internal matching. These devices are regularly used for broadband amplifiers. They often perform very well when a matching circuit is used to present a favorable impedance to the device at a specific frequency. However, over wide frequency ranges, the impedances of unmatched transistors are often quite difficult or even impossible to match, forcing the designer to either accept poor performance over the entire range, or resort to “channelizing” – breaking their overall band into smaller bands, designing individual amplifier chains for those sub-bands and then combining them into a single system.

Maintaining efficiency is absolutely critical in RF systems for several reasons. In hand-held applications, efficiency directly impacts battery life – an obvious key factor affecting a product’s overall performance. In addition, efficiency impacts cost in several ways. Increased efficiency delivers more RF output power per square millimeter of semiconductor material. In other words, there is a direct relationship between efficiency and RF semiconductor cost; improved efficiency can translate into smaller or fewer amplifier line-ups, and therefore a smaller bill of materials (BOM). If multiple amplifier chains are combined, there are significant savings in space and component costs of both the amplifier line-ups and a portion of the combining components. Finally, improved efficiency results in less waste heat, which can translate into reduced thermal management costs.

Compound Semiconductors
Advanced compound semiconductor technologies, with no internal matching, have enabled significantly increased amplifier bandwidth. These technologies have also markedly reduced capacitance for a given RF output power. Broadband matching networks therefore are able to provide an adequate match to the transistor over a greater bandwidth than is possible with traditional technologies such as LDMOS.

Designers are able to take advantage of the increased compound semiconductor device impedance in two ways. Greater bandwidths can be achieved for a given output power relative to that obtained using technologies such as LDMOS, or, the bandwidth can be left unchanged and the output power of the amplifier stage can be increased by selecting a larger device. While the advent of compound semiconductors has significantly improved wideband RF amplifier performance, efficiency is still quite poor relative to a narrowband design.

Changing the Equation with PowerBand™
TriQuint Semiconductor, Inc., has approached the challenge of wideband amplifier design from an entirely new direction through the development of its PowerBand™ RF discrete power transistors. PowerBand™ devices employ proprietary technology and are designed specifically to have broadband impedances that are constrained to domains to which a wideband circuit can readily match. The result is a massive improvement in wideband performance. Greater output power is obtained with PowerBand™ over a broader bandwidth, all the while offering break-through efficiency performance.

Because the PowerBand™ solution focuses on the union of impedances required by the device for optimal performance and uniting impedances obtainable by real world matching networks, performance trade-offs are similar to those in narrowband designs with regards to magnitude. For example, should the system require greater linearity, the designer can trade-off efficiency performance for the target linearity in roughly the same proportion as in a narrowband design because the PowerBand™ device is well matched over the entire band. When wideband amplifier systems are designed around traditional devices, the matching network struggles to keep the device matched at frequency range extremes. With non-PowerBand™ devices, performance trade-offs become less and less forgiving while overall sensitivity to normal variations in impedances grows more severe.

TriQuint announced the availability of product samples and wide-band RF demo board fixtures in November, 2008. The portfolio currently consists of two devices based on pHEMT technology (please see Figure 1), which operate from a 12v supply and generate 10 watts and 20 watts of P1dB RF power (respectively). Both devices are able to maintain greater than 50% efficiency across the band of 500MHz to 3GHz (please see Figure 2). This represents a vast improvement in efficiency and bandwidth compared to conventional RF discrete transistors. The devices are designed and characterized for CW operation; customers can order wideband RF fixtures for rapid evaluation.

TriQuint presently offers a single, versatile PowerBand™ LDMOS-based device. It generates 30 watts of P1dB CW output power with a 28v supply. An evaluation fixture designed to operate from 500MHz to 3GHz is available and demonstrates device efficiency of 45% across the entire band.

There are three PowerBand™ devices based on high-voltage pHEMT technology designed to operate with a 28v supply. These devices generate 20, 30 and 50 watts of P1dB power (respectively) and are specifically designed and characterized for pulsed applications.
TriQuint plans to expand its PowerBand™ portfolio with the introduction of 100 watt (P1dB) CW devices that will operate from a 28V supply. The new devices will utilize a larger version of the PowerBand™ package (please see Figure 3), which is designed with a flange for bolt-in installation. Both gallium nitride (GaN) and high voltage HBT-based technologies are being developed for release as 100 watt PowerBand™ devices in the summer of 2009.

Summary and Conclusion
Designing highly efficient, broadband amplifier systems has challenged RF engineers, often leading to a reliance on multiple amplifier line-ups in order to achieve high performance, high power broadband coverage. These approaches frequently resulted in larger BOMs or costly performance trade-offs. The advent of compound semiconductor technology and its evolution in broadband applications somewhat reduced the inherent trade-offs common to early broadband designs; however, these technologies were still limited in their ability to enable efficiencies greater than 30 percent when applied across a bandwidth of two octaves or more. The advent of PowerBand™ technology by TriQuint Semiconductor enables new cost-effective, high-efficiency broadband designs for signal jammers, specific radars and other common defense and wireless network applications. Offering power added efficiencies (PAE) of 45%-50% or more, TriQuint’s new PowerBand™ family also provides output power (P1dB) up to 50 watts across an unprecedented bandwidth: 500 MHz to 3 GHz. New HV-HBT and gallium nitride PowerBand™ products now in development will provide 100 watts of RF output power.

PowerBand™ offers an unparalleled combination of system advantages including greater efficiency, BOM reductions and wideband frequency coverage that free the designer from choosing between costly or inefficient trade-offs common to older broadband applications. PowerBand™ changes the equation, acting as the catalyst for next-generation designs that yield longer battery life in mobile devices and less DC power consumption / fewer thermal management requirements in network radio systems, all the while enabling simplified RF design and a wide range of other application specific savings.

Fore more information please e-mail inquiries or demo board requests below:

TriQuint Semiconductor, Inc.
www.triquint.com
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