Most applications requiring the generation of RF power depend on silicon and GaAs power transistors with typical outputs ranging from milliwatts to tens of watts. However, less visible but equally important are the wide array of industrial, scientific and medical applications that demand extremely high RF power levels to achieve their intended goals. To serve these applications, Freescale Semiconductor has introduced the MRF6VP11KH delivering peak RF output power of 1 kW at 130 MHz. The benefits of achieving this level of peak RF power are considerable from the perspectives of manufacturing, reliability and operating cost.
The MRF6VP11KH operates from 10 to 150 MHz, is fabricated using Freescale’s sixth-generation, very high voltage (VHV6) 50 V LDMOS technology and is the latest transistor in a growing portfolio of devices the company is developing for applications operating up to 450 MHz.
It operates in push-pull configuration and provides higher performance than bipolar and other MOSFET devices that are available for these applications. For signals with a pulse width of 100 µs and a 20 percent duty cycle, the MRF6VP11KH produces more than 1 kW at 1 dB gain compression with 65 percent efficiency and 27 dB power gain at 130 MHz.
It will produce 1.3 kW output power at the 3 dB compression point with 70 percent efficiency (see Figure 1). Additional specifications are contained in Table 1.
Typical applications for the MRF6VP11KH include medical and industrial magnetic resonance imaging (MRI), CO2 laser drivers for marking and cutting, industrial heat sealing, range-finding light detection and ranging (LIDAR), plasma generators for thin-film semiconductor processing, as well as broadcast transmitters and HF/VHF communications systems. Many of these applications require tens of kilowatts of RF output power. MRI systems, for example, employ power amplifiers that deliver 20 kW of peak RF power or more. To achieve these high power levels, the transmitters rely on amplifiers that have multiple stages, each stage employing one or more RF power transistors. With the levels of efficiency, gain and output power provided by the MRF6VP11KH, such a line-up is drastically reduced by up to 70 percent. This part count reduction significantly decreases board space requirements and manufacturing complexity, ultimately resulting in lower amplifier costs.
Amplifier Comparison
The dramatic advantages provided by the MRF6VP11KH can be demonstrated by comparing two amplifiers at the 2 kW level, the first using standard MOSFET or bipolar devices, and the second, the new MRF6VP11KH.
In each case, the amplifiers consist of low power drivers and high power amplifiers in several stages. In the first case, the 2 kW building block would typically require a single 15 W predriver, two 15 W drivers and eight final amplifier transistors for a total of three stages and 11 devices (see Figure 2).
Peak output power of this configuration would typically be 2.4 kW with power gain of 45 dB. Using the MRF6VP11KH, 2 kW of output power and gain of 50 dB can be achieved with only three devices in two stages: a single 10 W LDMOS driver (Freescale’s MRF6V2010N) and two MRF6VP11KH final amplifiers (see Figure 3).
Rugged Design
High power devices such as the MRF6VP11KH require the ability to withstand mismatch conditions well beyond their normal operating range. For example, the MRF6VP11KH can withstand extremely high impedance mismatches, and is rated for VSWRs as high as 10:1 at 50 V and 1 kW output power. It also incorporates electrostatic-discharge (ESD) protection against discharge while handling on the manufacturing floor.
This ESD protection provides ample gate voltage swing capability of –6 and +10 V, a very desirable attribute for higher classes of operation. Effective thermal management is essential when generating such high output-power levels from a single device, and considerable effort was spent to reach 0.13°C/W thermal resistant junction-to-case temperature in the design of the MRF6VP11KH.
In addition to the MRF6VP11KH, the company’s portfolio of 50 V VHV6 devices ranges from 10 to 450 MHz operation and includes the MRF6V2010N (10 W CW, 23.9 dB gain, 62 percent efficiency), the MRF6V2150N (150 W CW, 25 dB gain, 68.3 percent efficiency) and the MRF6V2300N (300 W CW, 25.5 dB gain, 68 percent efficiency). These devices are currently in production. The MRF6VP11KH is sampling now and production is expected in the fourth quarter of 2007.
Freescale Semiconductor,
RF Division,
Tempe, AZ (800) 521-6274,
www.freescale.com/rfpower.
RS No. 301