LDMOS FETs Set Benchmark for RF Power Transistors in Commercial Aerospace Systems
By Barry Manz, Contributing Editor

There are an array of applications in the lower microwave frequency ranges such as L-band and S-band that require the same levels of performance from RF power transistors as those employed in base stations for wireless networks. These applications, ranging from commercial aerospace systems to radar systems for airspace surveillance (air traffic control), as well as distance measuring equipment (DME), have often been served by bipolar junction transistors (BJTs), especially in radar systems. However, advances in LDMOS FETs are rapidly changing this paradigm, as their capabilities move upward in both operating frequency and pulsed RF power output. Freescale Semiconductor has been consistently expanding its portfolio of 50 V LDMOS for these applications in order to provide a cost effective alternative that delivers equal or better performance in every key figure of merit.

The company’s latest devices, introduced at the IMS 2009 conference, are excellent examples of how LDMOS technology is setting new benchmarks in what can be achieved in commercial aerospace applications. Perhaps the most noteworthy devices among the five comprising the announcement are the first 1-kW 50 V LDMOS FET designed for operation at L-band (780 MHz to 1215 MHz). This and the other LDMOS FETs deliver the highest RF output power, efficiency, and gain available among devices dedicated to these applications. All are intended to be used with pulsed signals characterized for their intended applications. Freescale also simultaneously launched several products for GSM applications at IMS 2009 that also deliver the highest performance in their class .

50 V L-band Devices
Freescale’s three new 50 V L-band devices are designed for operation with a 128 µs pulse width and 10% duty cycle. The MRF6VP121KH/HS (Figure 1) delivers 1 kW of peak RF output power and 100 W average power with 20 dB of gain and 56% drain efficiency at 1030 MHz. With an RF output power of 500 W and 50 W average output power, the MRF6V12500H/HS provides 19 dB gain with 60% drain efficiency at 1030 MHz. The last L-band device in the lineup is the MRF6V12250H/HS, which delivers 275 W peak and 27.5 W average output, with 20.3 dB of gain, and 65.5% drain efficiency at 1030 MHz, while being able to sustain 10:1 VSWR at rated power.

S-band Devices
Freescale’s RF power transistors designed for operation in the higher S-band frequency range are specified for signals with a 100 µs pulse width and 20% duty cycle. The new devices for this band operate from up to 32 V and can deliver their rated power into a 10:1 VSWR at 3.5 GHz. The MRF7S35120HS (Figure 2) delivers 120 W peak and 24 W average RF output power with 12 dB gain and 40% efficiency at 3.5 GHz. The MRF7S35015H provides 15 W of peak and 3 W of average RF output power with 16 dB of gain and 41% efficiency.

The new devices are RoHS compliant and incorporate electrostatic discharge (ESD) protection, which not only makes them less susceptible to stray transient voltage spikes during assembly, but enables a broad gate voltage swing of -6 V to +10 V that helps improve performance when the devices are operating in higher efficiency modes, such as Class C.

A Growing Portfolio
Freescale has been steadily broadening its family of devices for commercial aerospace applications for more than 2 years, and today offers the broadest range of LDMOS FETs for these applications. The MRF6V4300N, for example, is tailored for operation at HF to UHF communications frequencies. It delivers RF output power of 300 W CW from 10 to 600 MHz, and at 450 MHz produces gain of 22 dB and 60% drain efficiency. The device is housed in Freescale’s RoHS compliant, cost-effective over-molded plastic package, which offers the tight mechanical tolerances and very low thermal resistance of 0.24º/W that makes heat dissipation management considerably easier and helps reduce heat sink size. In addition to the MRF6V4300N, Freescale’s 50 Vdc MRF6V14300H FET produces 330 W of pulsed RF output power from 1.2 to 1.4 GHz with 18 dB of gain and up to 60.5% drain efficiency.

To complement the higher-power L-band devices, the company offers the MRF6V10010N, a driver amplifier that produces up to 10 W from 960 MHz to 1.4 GHz. By employing this device along with the cost-effective MMG3014N pre-driver in a three-stage lineup, the three devices can deliver up to 330 W of peak RF output power at 1.4 GHz (300 µs pulse, 12% duty cycle), with 62 dB of total gain, and an overall efficiency up to 59.5%, including combining losses. Freescale made news in 2007 when it introduced the MRF6VP41KH, which was Freescale’s first LDMOS FET to deliver 1 kW of RF power (100 µs pulse, 20% duty cycle). It has efficiency of up to 64 percent, 20 dB power gain at 450 MHz, and can produce RF output power up to 1 kW at 1 dB compression.

Together, Freescale’s device portfolio now includes models of operation from HF through S-band and will continue to grow in the coming year. The MRF6VP121KH/HS, RF6V12250H/HS, MRF7S35120HS and the MRF7S35015H devices are in full production. The MRF6V12500H/HS is expected to be in production in September. All devices are sampling, and reference test fixtures are available now. Large-signal models for L-band devices are expected in September. The MRF6V4300N, MRF6V14300H, MRF6V10010N, and MRF6VP11KH are currently in full production and supported by test fixtures. For more information about all the devices, visit our website.

FREESCALE
www.freescale.com
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