Power Transistors Reach New Levels

Sept. 21, 2010
Improved impedance matching and thermal design, combined with enabled RF transistors to reach new levels of output power.

High-frequency solid-state poweramplifier designers have never enjoyed a wider choice of large-signal active devices for both continuous-wave (CW) and pulsed applications. At one time, the selection process amounted to finding a silicon bipolar transistor with adequate gain and output power over a frequency band of interest. With the development of newer epitaxial materials with outstanding thermal characteristics, such as silicon carbide (SiC) and gallium nitride (GaN), amplifier designers now have some excellent high-power RF and microwave transistors at their disposal.

One of the major proponents of power transistors based on SiC material, Microsemi Corp., has managed to exceed the 2-kW mark with pulsed output power in its model SiC transistor (see this month's Defense Electronics for an extended review). It produces 2.2 kW of pulsed output power at ultrahigh-frequency (UHF) signals from 406 to 450 MHz. SiC is a wide-bandgap material that can handle operating temperatures as high as +350C, making it suitable for extremely high power devices. For example, the material's high-temperature capabilities can reduce packaging requirements. By seizing on these capabilities, Microsemi has developed a series of high-power pulsed devices for radar systems, including this latest model 0405SC-2200M UHF device.

The 0405SC-2200M is designed to provide its rated output power at 1-dB compression and with better than 8 dB typical power gain. The commongate, Class AB device is designed for pulsed UHF weather radars and over the horizon radar applications. The model 0405SC-2200M SiC transistor is supplied in a hermetic, single-ended package for common-gate Class AB amplifier designs. It uses high-temperature gold metallization and gold bond wires for high reliability. Four devices can be combined with a suitable low-loss four-way power combiner to achieve about 8 kW output power from 406 to 450 MHz. It features drain efficiency about 55 percent at 450 MHz (minimum of 50 percent) at a supply voltage of +125 VDC.

The 0405SC-2200M device is an evolution of the company's model 0405SC-1500M SiC power transistor, which is capable of 1500 W pulsed output power from 406 to 450 MHz when driven by an input signal at 270 W. The packaged transistor features a simple single-ended design for ease of combining multiple devices for higher output powers. The device, which is geared for medium-duration pulses of about 300 μs at a 6-percent duty cycle achieves 8-dB typical power gain across its bandwidth. Its drain efficiency is 45 percent at 450 MHz. It runs at a supply voltage of +125 VDC and is rated for a maximum junction temperature of +250C.

In the area of GaN transistors, Nitronex offers its model NPT1007 for applications up to 1.2 GHz. The packaged transistor delivers 200 W output power at 900 MHz with 18.3 dB gain. The drain efficiency under those conditions is 63 percent. It consists of two power transistors, each capable of 100 W output power, impedance matched and combined in a four-lead Gemini package.

According to Ray Crampton, Director of Marketing at Nitronex, "The NPT1007 was developed while working with leading power amplifier designers who needed a smaller, more efficient solution than was available on the market to date." Usable with operating voltages from +14 to +28 VDC, the NPT1007 is lead free and RoHS compliant and is available in a thermally enhanced ceramic air-cavity bolt-down package.

Also based on the company's GaNon- silicon technology, the model NPT1012 transistor is designed for applications from DC to 4 GHz. The NPT1012 provides more than 20 W of output power (at 1-dB compression) from 1.0 to 2.5 GHz (and as much as 25 W output power at 3-dB compression) with over 50 percent drain efficiency. According to Gary Blackington, Vice President of Sales and Marketing at Nitronex, "The new NPT1012 25-W GaN power transistor has been designed specifically to improve broadband power performance by addressing thermal management. Designers can use the NPT1012 transistor to develop compact, multi-octave power amplifiers that simultaneously meet RF and thermal requirements."

For higher-power operation, the company's GaN-on-silicon model NPT1007 high electron mobility transistor (HEMT) is designed for narrowband and broadband applications from DC to 1200 MHz. It supplies 200 W CW output power at 900 MHz at 3-dB compression in a quadrature combined or push-pull configuration. It can operate on supplies of +14 to 28 VDC with drain efficiency of typically 63 percent for 3-B compression operations.

Cree has developed its model CGH31240F high electron mobility transistor (HEMT) based on GaN for applications from 3.1 to 3.4 GHz. When operating with 300-microsecond pulses at a 10-percent duty cycle, the device achieves 240 W peak power with 16.6 dB gain and 50-percent efficiency at 2.8 GHz. The firm's model CGH40120F GaN HEMT is an unmatched +28-VDC device rated for 120 W saturated output power. It has been used in a reference amplifier with 1200-to-1400-MHz instantaneous bandwidth, 100 W CW typical output power, 16-dB typical small-signal gain, and 75-percent typical power-added efficiency.

HVVI Semiconductors uses silicon MOSFET technology for its model HVV0912-150 L-band avionics transistor. Suitable for use from 960 to 1215 MHz in L-band avionics applications such as TCAS, IFF, and DME systems, it delivers 150 W output power with 20-dB gain when driving 10-μs pulses at a 10-percent duty cycle. It can operate on supplies from +24 to +50 VDC and delivers 43-percent efficiency. Its unique vertical device structure allows it to operate into mismatches as severe as a 20.0:1 VSWR without damage.

Integra Technologies also provides transistors for solid-state radar systems, including silicon bipolar transistors, such as the model IB1011S1500. When fed with a 150-W pulsed (10-μs, 1-percent duty cycle) input signal at 1030 MHz, it yields 1432 W peak output power with 48.8 percent efficiency. It is suitable for L-band radar systems from 1030 to 1090 MHz. The company also supplies its model IB0912M600 bipolar transistor for L-band TACAN from 960 to 1215 MHz. It offers 845 W peak output power and better than 56-percent efficiency at 960 MHz when driving a 90-W pulsed input signal. Both transistors are housed in beryllium-oxide (BeO) packages for good thermal dissipation.

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Long-time supplier of high-power RF transistors, Freescale Semiconductor has several series of transistors based on silicon laterally diffused metal-oxide-semiconductor (LDMOS) device technology, using either +28- or +50-VDC supply voltages. Model MRF6S18100N, for example, is a +28-VDC LDMOS device designed for GSM cellular base station applications from 1805 to 1990 MHz. Supplied in a TO-270 package, it delivers 100 W output power at 1990 MHz with typical gain of 14.5 dB and drain efficiency of 49 percent. It delivers typically 110 W output power at 1-dB gain compression.

Operating at the higher +50-VDC supply, the model MRF6V12500H LDMOS transistor is designed for pulsed applications from 965 to 1215 MHz. It draws 200 mA quiescent current from a +50-VDC supply, delivering 500 W peak output power (50 W average output power) at 1030 MHz, when working with a 128-μs pulse width signal at 10-percent duty cycle. The power gain under those conditions is 19.7 dB with drain efficiency of 62 percent. It can handle a load mismatch equivalent to a 10.0:1 VSWR without damage, when delivering 500 W peak power at 1090 MHz. Another +50-VDC LDMOS device, model MRF6V1430H, delivers 330 W peak output power with pulsed (300-μs, 12-percent duty cycle) signals from 1.2 to 1.4 GHz. It features power gain of typically 18 dB with drain efficiency of 60.5 percent.

The firm offers an excellent, free 12-page white paper on its silicon LDMOS device technology, "50-V RF LDMOS: An ideal RF power technology for ISM, broadcast, and commercial aerospace applications," which provides an introduction to the use of these high-power, high-voltage transistors. Its 50-V LDMOS devices feature enhanced electrostatic-discharge (ESD) protection that can tolerate moderate reverse bias without damage and a robust Class C design that works with high RF input power levels.

IXYS RF, with 150-V MOSFETs capable of as much as 550 W CW output power at 175 MHz, and P1dB (www.P1db.com), with silicon bipolars offering as much as 200 W output power in DME and TACAN applications from 960 to 1215 MHz. TriQuint Semiconductor offers its Powerband GaAs PHEMT devices capable of 50-W pulsed output power from 0.5 to 2.0 GHz.

The STAP1011-180 N-channel enhancement-mode lateral silicon MOSFET from ST Microelectronics is designed for avionics applications from 1030 to 1090 MHz. It provides 180 W pulsed output power (and typically 195 W power) with 100- μs pulses at a 10-percent duty cycle. The plastic-packaged device, which can dissipate as much as 500 W power, delivers 10-dB gain over its operating frequency range.

The PTFB213004F LDMOS fieldeffect transistor (FET) from Infineon Technologies is designed for use in cellular communications amplifiers operating from 2110 to 2170 MHz. It is characterized by means of two-tone testing and is ideal for complex modulated signal formats, including wideband code division multiple access (WCDMA). The transistor can generate as much as 300 W peak output power and provides 250 W peak envelope power (PEP) when driven with two tones as 2140 and 2141 MHz and operating from +30 VDC and quiescent current of 2.4 A. Under those conditions, the typical gain is 18 dB, with typical drain efficiency of 37 percent and typical intermodulation distortion (IMD) of -30 dBc.

These high-power devices have generally been designed for frequencies of 2 GHz or less, using silicon-based semiconductor technologies. At higher frequencies, solid-state output power becomes more scarce and devices depend more on epitaxial materials such as gallium arsenide or GaN. For example, Toshiba America Electronic Components has developed a 50-W GaN HEMT with operation from 7.7 to 8.5 GHz. Designed for satcom applications, it delivers typical output power of +47 dBm with 11-d linear gain. The device draws 5 A current at +24 VDC. And TriQuint achieves 100 W output power and 8.5-dB gain from DC to 18 GHz with its GaN-on-SiC technology embodied in its model TGF2023-20 discrete HEMT. The transistor has 55 percent power-added efficiency.

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