LDMOS FETS Serve 330 W For L-Band Radar Systems

Solid-state power for commercial wireless base-station transceivers has been dominated by the laterally diffused metal-oxide-semiconductor (LDMOS) field-effect transistor (FET) since the device first became available in the 1980s. In spite of its ruggedness and attractive characteristics such as high linearity, gain, and efficiency, the siliconbased device has not had the same impact on L-band radar and avionics applications. Still, the MRF6V14300H 50-V LDMOS FET from Freescale Semiconductor (www.freescale.com/rfpower) may change all that. With 330 W of pulsed output power from 1200 to 1400 MHz, 18-dB gain, and 60.5-percent drain efficiency, the MRF6V14300H outshines competing devices and technologies currently available for pulsed operation at L-band frequencies.

The MRF6V14300H is the company's first 50-V LDMOS FET designed for avionics and radar applications and will be joined later by other devices. It is part of Freescale's expanding portfolio of 50-V LDMOS devices, which continues to grow in performance and targeted applications since the first 50-V transistors were introduced in 2006. Devices are now available from HF through L-band and are tailored for communications systems, industrial, scientific, and medical (ISM) products, analog and digital VHF and UHF broadcast transmitters, and now L-band radars and avionics equipment.

The MRF6V14300H (Fig. 1) and its siblings benefit from the company's long experience in refining earlier 28-V LDMOS FET designs, millions of which are used in cellular base stations worldwide. The 50-V Very High Voltage Sixth Generation (VHV-6) process in which the MRF6V14300H is fabricated extends these fundamental strengths to highervoltage operation, which provides inherent benefits. For example, the ability to operate at a higher operating voltage enables increased power densities to be achieved along with higher gain and efficiency, and better thermal characteristics.

While these characteristics are advantageous in general, they are especially appealing in radar system applications, which typically have RF output levels of several kilowatts or more and employ many gain stages, each consisting of driver and output stage RF power transistors. Increases in gain, efficiency, and output power have a significant positive impact on the design of such a system because fewer devices and gain stages are required to produce a specific output. This translates into lower costs, reduced design complexity, a smaller footprint, and lower system power consumption, which for a radar transmitter can be thousands of dollars per year. Lower junction-to-case thermal resistance (R_?JC), which in the case of the MRF6V14300H is 0.13oC/W (the lowest thermal resistance of any competitive device), reduces the requirements for heat sinking and cooling overhead needed by the system, which can also play a role in reducing complexity, cost, size, and power consumption.

To complement the MRF6V14300H in avionics and radar applications, Freescale has introduced a new LDMOS FET driver (the MRF6V10010N) that delivers 10 W output power from 960 to 1400 MHz. When used along with a Freescale MMG3014N predriver, the MRF6V10010N and MRF6V14300H can be configured in a three-stage lineup to produce peak RF output power of 330 W at 1400 MHz with a 300 s pulsed signal and 12-percent duty cycle. The lineup produces 62 dB total gain and draws 11.1 A current. The overall efficiency is 59.5 percent including all three stages and associated combining losses (Fig. 2).

The MRF6V14300H and MRF6V10010N employ electrostatic discharge (ESD) protection, a characteristic of all the company's 50-V LDMOS devices. This feature makes them less susceptible to damage from handling on assembly lines. It has the additional benefit of producing a very wide gate voltage swing (-6 to +10 V), which is useful when the devices are used in higher-efficiency modes such as Class C operation. The MRF6V14300H is housed in an NI-780 air-cavity ceramic package and is internally matched. It can withstand a maximum VSWR mismatch of 3.0:1 at 1400 MHz when operating at 50 V and producing 330 W. Detailed specifications are shown in the table.

The MRF6V10010N is housed in an over-molded plastic PLD-1.5 package and can withstand a maximum VSWR mismatch of 10.0:1 at 1400 MHz when operating at 50 V and producing 10 W. Both devices are RoHS compliant. The MRF6V10010N is currently in production and samples of the MRF6V14300H are available, with production expected in the fourth quarter of 2008. For engineers working with computer-aided-engineering (CAE) software, large-signal models will be available later in the year for both devices, and a broadband reference test fixture is currently available for the MRF6V14300H. Freescale Semiconductor, RF, Analog, and Sensors Group, 2100 E. Elliot Rd., Tempe, AZ 85284; (800) 521-6274; Internet: www.freescale.com/rfpower.