LDMOS FETs Reach 1-kW Peak Output Power

This robust RF power transistor combines high efficiency and gain to reduce the manufacturing cost of MRI and other industrial and medical systems.

Solid-state RF power for industrial-scientific-medical (ISM) applications usually requires multiple transistors to reach levels of 1 kW and more. Magnetic-resonance-imaging (MRI) systems, for example, employ power amplifiers that can deliver in excess of 20 kW of peak RF power. To serve these applications, Freescale Semiconductor (Tempe, AZ) has introduced the MRF6VP11KH, which delivers RF output power of 1 kW at 130 MHz—currently the highest-power commercially available RF power LDMOS transistor.

The MRF6VP11KH transistor (see figure) employs Freescale's sixth-generation, very high-voltage (VHV6) 50V LDMOS technology and joins a family of VHV6 LDMOS devices the company introduced in 2006 for applications to 450 MHz. It operates in push-pull configuration from 10 to 150 MHz and is designed to provide higher performance than bipolar and other MOSFET devices typically employed in these applications. For signals with pulse width of 100 µs and 20-percent duty cycle, the MRF6VP11KH delivers more than 1 kW at the 1-dB gain compression point with 65-percent efficiency and 27-dB power gain. It achieves 1.3 kW output power at 3-dB compression with 70-percent efficiency.

Typical applications for the MRF6VP11KH range from CO2 laser power amplifiers employed in industrial marking and cutting, and range-finding light detection and ranging (LIDAR), to plasma generators for thin-film semiconductor processing, and medical and industrial uses of MRI. Achieving these extremely high RF power levels requires a combination of low-power drivers and high-power amplifier devices in several stages. The high power level delivered by this device, with unprecedented levels of gain, allows power-amplifier designers to considerably simplify the line-ups.

For example, a 2 kW building block typically uses one 15-W pre-driver, two 15-W drivers, and eight final transistors for a total of three stages and 11 devices. Peak output power is 2.4 kW and power gain is 45 dB. Using the MRF6VP11KH, 2 kW output power and gain of 50 dB can be achieved with a single 10-W LDMOS driver (the MRF6V2010N from Freescale) and two MRF6VP11KH final amplifiers. Since only one 2:1 power combiner is required, combining losses are much lower, costs are lower, and reliability is higher.

The MRF6VP11KH is designed to withstand extremely high impedance mismatch levels. It is rated for VSWRs as high as 10.0:1 at 50 V and 1 kW output power. It also incorporates electrostatic-discharge (ESD) protection against damage while handling on the manufacturing floor. This ESD protection still provides ample gate voltage swing capability of –6 V and +10 V, a very desirable attribute for higher classes of operation.

Effective thermal management is a key to generating such high output-power levels from a single device. Considerable effort was spent to reach 0.13 degree CW thermal resistant junction to case temperature. This, along with best-in-class efficiency, combine to produce longer operating life and reduced heat sink and cooling requirements.

Freescale Semiconductor, RF Division, 2100 E. Elliot Rd., Tempe, AZ 85284; (800) 521-6274, Internet: www.freescale.com/power

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