RF Transistors Add Power, Subtract Heat

High-power RF transistor developers face the constant challenge of dissipating massive amounts of heat from small devices in order to achieve higher output-power levels. Ideally, the energy put into an RF transistor would be converted directly to RF output power, but such 100-percent drain efficiency can only be achieved in an ideal world. In reality, more than one-half of the power supplied to an RF transistor must typically be dissipated as heat, and RF transistor manufacturers have met such challenges through the use of thermally conductive materials in innovative packages. By raising the amount of power that can be delivered from a single device, RF power transistor suppliers have cut down on the number of amplifier stages and devices needed to reach a given output-power level in a high-power amplifier (HPA), whether for commercial, industrial, medical, or military applications. What follows is a sampling of recent highpower device introductions from some leading transistor suppliers.

For simpler installation into highfrequency circuits, many modern highpower RF transistors are internally impedance matched, so that input and output ports are already at 50 ohms. Integra Technologies (www.integratech.com), for example, offers lines of transistors that actually resemble amplifier circuits that have been dubbed the Miniaturized Power Amplifier (MPA) devices. Based on laterally diffused metal-oxide-semiconductor (LDMOS) technology, initial MPA devices have been developed for S-band applications at 2.7 to 3.1 GHz and from 3.0 to 3.5 GHz. The gold-metalized transistors are constructed to handle biasing conditions from Class A through Class B and to run under a wide range of pulsed (different pulse widths and duty cycles) conditions.

Model MPAL3035M15 is rated for 15 W typical output power, but can be used for output levels as low as 5 W while maintaining good output pulse fidelity. Model MPAL3035M30, which is rated for 35 W peak pulsed output power from 3.0 to 3.5 GHz for S-band pulsed radar systems, can be used to supply output-power levels as low as 1 W. It offers 11 dB minimum power gain with 0.3-dB maximum pulse amplitude droop. It can tolerate load mismatches equivalent to a 3.0:1 VSWR at the rated output power without damage.

HVVi Semiconductors, Inc. (www.hvvi.com) has added its patent-pending High Voltage Vertical Field Effect Transistor (HVVFET) technology to the device options for building high-power RF/microwave amplifiers for commercial and military applications. The vertical transistor architecture promises increased frequency bandwidth at higher voltage and higher power levels than traditional silicon transistor architectures for initial applications in radar and avionics systems. The substrate of the HVVFET substrate doubles as the transistor's drain. An HVFET transistor depletes vertically into the substrate as the supply voltage is fed to the drain. The device architecture approaches planar breakdown in the vertical drain region, standing off maximum voltage with minimum on resistance. This architecture offers potential for high device density with low parasitic capacitance (for highervoltage, higher-frequency operation). Performance tends to improve at higher voltages, clearing the way for future, higher-voltage device designs.

HVVi's first three products are designed for pulsed L-band applications, such as IFF, TCAS, TACAN, and Mode-S radar systems. The three transistors are models PVV1011-300, PVV1214-25, and PVV1214-100. All three devices are designed to operate at +48 VDC. The firm's HVVFET wafer process is extremely scalable, allowing the development of higherpower devices with the same layout and design simply by increasing the size of the transistor die.

Model PVV1011-300 delivers 300 W pulsed output power from 1030 to 1090 MHz with 15 dB gain and 48-percent efficiency when evaluated with a 50-microsecond pulse-width signal at a pulse period of 1 ms. The transistor can withstand load conditions equivalent to a VSWR mismatch of 20.0:1 at all phase angles and under the full-rated output power.

Model PVV1214-25 provides 25 W output power from 1200 to 1400 MHz with a 200-microsecond pulse-width signal at a pulse duty cycle of 10 percent. At full rated power, it delivers 17.5 dB typical gain. Model PVV1214-100 provides 100 W output power from 1200 to 1400 MHz with 19.5 dB typical gain. These latter two devices are both designed to withstand an output load mismatch equivalent to a 20.0:1 VSWR at the rated output-power levels and nominal operating voltages. The firm's President and Chief Executive Officer (CEO), Wil Salhuana, volunteers that "while currently used silicon RF transistor technologies such as bipolar and LDMOS have served radar and avionics designers well, they have hit a ceiling in terms of performance. By creating the first high-frequency, high-voltage vertical field-effect transistor, we have redefined the performance capabilities of the discrete silicon power transistor and opened the door to a vast array of new applications." The vertical device technology is legally protected in terms of 10 United States patents and seven foreign patents filed. In addition to initial applications in high-power pulsed L-band radar systems, the transistor technology is expected to power new applications across wireless industries as diverse as cellular infrastructure, broadcast, and Industrial-Scientific- Medical (ISM) band applications.

Freescale Semiconductor (www.freescale.com) recently added to its highpower LDMOS portfolio with a pair of N-channel enhancement-mode devices, the model MRF6V10010N for use from 960 to 1400 MHz and the model MRF6V1430H for applications from 1200 to 1400 MHz. The former delivers 10 W peak power with 25 dB gain and impressive 69-percent drain efficiency when powering 100-microsecondpulse- width signals over a 20-percent duty cycle. The higher-power model MRF6V1430H yields 330 W peak output power with 18 dB gain and 60.5-percent drain efficiency when operating with 300-microsecond-pulsewidth signals over a 12-percent duty cycle. Both devices are RoHS compliant and ESD protected; the higher-power transistor is also internally matched to 50 ohms for ease of installation into high-frequency circuits.

In recent years, transistor specifiers have had choices other than highfrequency devices based on silicon and GaAs substrate materials, with the emergence of commercial galliumnitride (GaN) and silicon-carbide (SiC) transistors from several manufacturers. For example, Cree (www.cree.com) recently announced its unmatched model CRF24060 SiC transistor for commercial and military broadband applications to 2.4 GHz. The +48-VDC MESFET device delivers as much as 60 W output power at 1500 MHz with 13-dB gain and 45-percent drain efficiency. To assist amplifier designers, the firm offers typical scattering (S) parameters for the device from 100 to 3000 MHz on its web-page-based data sheets.

Earlier this year, Nitronex (www.nitronex.com) announced its model NPT1004 high-electron-mobilitytransistor (HEMT) device capable of 45 W output power to 4 GHz when operating at +28 VDC with pulsed or high peak-to-average-ratio (PAR) signals. Based on the company's patented GaN-on-silicon device technology, the transistor is housed in a unique thermally enhanced plastic package for effective heat dissipation. Also this year, the firm announced that it had entered into a Memorandum of Understanding with noted microwave component and subassembly supplier Merrimac Industries (www.merrimacind.com) to develop highly integrated GaN-based power amplifiers using Merrimac's proprietary Multi-Mix multilayer circuit technology. The outstanding thermal dissipation of the multilayer circuit designs support the long-term reliability of Nitronex's high-power RF transistors.

For those who may question the reliability of GaN-based RF power transistors, Nitronex now offers a reliability calculator on its web site. Available for free download, the reliability calculator incorporates pre-programmed device parameters that help calculate the performance and mean time to failure (MTTF) for a wide range of the firm's GaN-on-silicon RF power transistors. Users can modify input values for the calculator, such as flange temperature, gain, output power, drain efficiency, and thermal resistance and calculate device performance, including the expected MTTF. For more information on the reliability calculator from Nitronex, refer to the story in the July issue of Penton's Military Electronics, available on the Microwaves & RF web site at www.mwrf.com.

Foundry service provider TriQuint Semiconductor (www.triquint.com) also supplies an extensive line of silicon LDMOS power transistors for wireless base stations. The devices, initially added through the acquisition of transistor house Peak Devices in 2007, are available for power levels from 30 to 180 W at frequencies from 865 MHz to 2.7 GHz.

STMicroelectronics (st.com) offers its SD293X and SD393X RF MOSFETS for Industrial-Scientific-Medical (ISM) band applications. Based on the firm's gold-metalized N-channel RF MOSFET technology, the devices are said to achieve higher RF power gain through the use of a shield structure that reduced feedback capacitance. For example, the model SD294X series of devices, direct descendant of the company's SD293X series, deliver output-power levels from 175 to 350 MHz at ISM frequencies (compared to a top output of 300 W for the older process).

The model SD2941-10 operates at +50 VDC and supplies 175 W output power at 175 MHz with 21.5-dB typical gain. It features thermal junction resistance of 0.45C/W in a single-ended package. For more power at the same frequency, the firm's model SD2942 operates at +50 VDC and provides 350 W output power at 175 MHz with 17.5-dB typical gain with 55-percent minimum drain efficiency and thermal junction resistance of 0.35C/W in a push-pull package. Model SD2943 also operates at +50 VDC and yields 350 W output power at 30 MHz with 25-dB typical gain in a single-ended package. These transistors are suitable for amplifiers for applications in NMR, FM/VHF broadcast, industrial lasers, RF heating, plasma generators, and single-sideband (SSB) communications systems.

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Tyco Electronics, M/A-COM (www.macom.com) offers a variety of different RF/microwave power transistors, including silicon bipolars, silicon MOSFETs, GaAs MESFETs, and silicon LDMOS devices. For example, the firm's model MAPRST1030-1KS is an NPN silicon power transistor for pulsed avionics systems. Supplied in a RoHS-compliant package, the goldmetalized, Class C device delivers 1000 W output power at 1030 MHz when operating at +50 VDC with 10-microsecond pulses at 1-percent duty cycle. It achieves 8.74-dB gain with better than 50-percent drain efficiency. The firm's model MAPR-000912-500S00 is also a pulsed avionics transistor, for applications from 960 to 1215 MHz. The Class C device provide 598 W output power with 50.9-percent drain efficiency and 9.77-dB gain at 960 MHz and +50 VDC, and 54 W output power with 56.1-percent drain efficiency and 9.44-dB gain at 1215 MHz and +50 VDC with short-duty-cycle pulsed signals. Model MAPLST2122-090CF is an LDMOS device capable of 90 W output power from 2100 to 2200 MHz operating from +28 VDC.

IXYS RF (www.ixysrf.com) offers a wide range of 150-V linear Z-MOS devices for FM and UHF use, including the model IXZ210N50L singleended device with 300 W output power and 14-dB gain and the model IXZ2210N50L push-pull device with 550 W output power and 14-dB gain. The firm's model IXZ215N12L is a single-ended device with 150 W output power and 13-dB gain at 175 MHz.

Advanced Semiconductor, Inc. (www.advancedsemiconductor.com) replacement parts for transistors from Motorola, Philips Semiconductors, and SGS Thomson. For military communications, for example, the company offers the +28-VDC model UML125B with 125 W output power and 7-dB gain at 400 MHz and 100 W output power and 5.5-dB gain at 500 MHz. The transistor has 55-percent drain efficiency at 500 MHz.

Infineon Corp. (www.infineon.com) also offers a wide range of power devices, including the model PTFA092201E/F with 220 W output power from 920 to 960 MHz. Intended for EDGE and WCDMA amplifier applications, the device is supplied in single-ended screw-down flange/ single-ended earless-flange housings. The internally matched GOLDMOS RF LDMOS FET provides typical two-carrier WCDMA performance at 960 MHz and +30 VDC of 55 W average output power, 18.5-dB linear gain, 30-percent drain efficiency, and intermodulation-distortion (IMD) performance of -37 dBm. The firm's model PTFA082201E/F LDMOS FET also operates at +30 VDC, delivering 220 W output power from 869 to 894 MHz with 18.5-dB gain. It features 30-percent drain efficiency and -37 dBm IMD performance. Under CW conditions, it provides 250 W output power at 1-dB compression and +30 VDC at 894 MHz.

Additional high-power RF transistor suppliers include Ericsson (www. ericsson.com), Microsemi (www.microsemi.com), NXP Semiconductors (www.nxp.com, the former Philips Semiconductors), ON Semiconductor (www.onsemi.com), P1db (www.p1db.com), and Renesas (www.america.renasas.com). For example, NXP recently introduced the +32-VDC model BLF6G27-135 LDMOS power transistor with typical 20 W single-carrier average output power from 2500 to 2700 MHz. It delivers 16 dB power gain over that range, with drain efficiency of 22.5 percent and ACPR of -52 dBc. The device features integrated ESD protection. The firm also recently announced the BLF369 LDMOS +32-VDC transistor for VHF applications, with 500 W pulsed output power at 225 MHz with 18 dB gain and 60-percent drain efficiency operating under Class AB conditions.

P1db offers extensive lines of silicon bipolar power transistors for applications from 1 through 4200 MHz with as much as 450 W output power at 450 MHz for UHF pulsed radars.

For a complete listing of suppliers, refer to the print or online versions of the Microwaves & RF Product Data Directory at www.mwrf.com.