Power transistors have typically traded performance for instantaneous bandwidth. Most devices show a huge drop in output power, gain, and efficiency when switching from relatively narrowband applications to circuits with wide instantaneous bandwidth, such as with pulsed RF signals. The new series of PowerBand discrete power transistors from TriQuint Semiconductor have been designed to be the exception to this rule, with excellent performance whether used in narrowband or wideband applications. These robust transistors are well suited for systems using either continuous-wave (CW) or pulsed and modulated signals, including radar, electronic-warfare (EW), and wireless communications systems.
The new line of PowerBand discrete power transistors currently includes six power transistors. As evidence of the flexibility of the PowerBand approach, the new transistors are based on two different device processes: silicon lateral diffused metal oxide semiconductor (LDMOS) and gallium arsenide (GaAs) pseudomorphic high-electron-mobility-transistor (pHEMT) technologies. The transistor covers a total frequency range of 500 MHz to 3 GHz with as much as 50 W output power at 1-dB compression at 2 GHz.
According to TriQuint President and Chief Executive Officer (CEO) Ralph Quinsey, "PowerBand changes the wireless equation, creating an opportunity to save a tremendous amount of space, cost, and energy. Because PowerBand efficiently delivers high power across unprecedented bandwidth, an RF design may require only one transistor line-up instead of several. This fact directly impacts the bill of materials and size of end user products by substantially reducing space dedicated to RF."
Bill McCalpin, PowerBand Co-Inventor and General Manager, TriQuint Colorado Design Center, adds that "the incredible performance of PowerBand is the first thing that evaluating engineers recognize as truly outstanding. A traditional high-power RF transistor is designed to operate across a narrow frequency range, such as 2.53 to 2.65 GHz. Within that range it delivers power relatively efficiently. But as bandwidth increases, performance falls. PowerBand is totally different in its ability to deliver high power and high efficiency performance across a much wider frequency range, from 500 MHz to 3 GHz."
High efficiency results in less heat generated by high-power RF/microwave transmitters, and less complexity and cost in controlling and dissipating the heat that is generated. In mobile devices, higher efficiency results in longer operating time on a battery and less heat generated in portable systems. Although the PowerBand technology has been applied to silicon LDMOS and GaAs pHEMT processes for the first set of power transistors, it is also applicable to other high-power device technologies, such as processes based on silicon carbide (SiC) and gallium nitride (GaN) wafers.
The first series of PowerBand devices include one silicon LDMOS power transistor, model T12003028-SP. The discrete device is designed for use with +28-VDC power sullies and at frequencies from 500 MHz to 2 GHz. When tested for wideband, instantaneous use of its operating bandwidth, such as with high-rise-time pulsed signals, it delivers 30 W output power at 1-dB compression with 10-dB typical gain and 45-percent power-added efficiency. For more traditional narrowband use, it can generate 45 W output power at 2 GHz with 14 dB gain and 59-percent drain efficiency, for a +28 VDC supply with 450 mA quiescent current. The LDMOS transistor exhibits typical input capacitance of 73 pF and typical output capacitance of 23 pF. It has junction-to-case thermal resistance of 1.3C/W and minimum drain-to-source breakdown voltage of 65 V. It shows third-order intermodulation distortion of typically -31 dBc when measured with tone spacing of 100 kHz, quiescent current of 450 mA at +28 VDC, and 45 W peak envelope power (PEP). The high-power LDMOS transistor, which is supplied in a flange-mount transistor package (see figure), exhibits input return loss of typically 10 dB. It operates into a 10.0:1 VSWR mismatch load with no degradation in output power.
The remaining currently available PowerBand power transistors are discrete GaAs pHEMT devices, all usable for either wideband or narrowband applications with little trade off in performance. Model TIP3002012-SP provides 20 W output power at 1-dB compression across its full instantaneous bandwidth of 500 MHz to 3 GHz with 10 dB gain and 50-percent power-added efficiency; it is designed to run on a +12-VDC supply. For pulsed applications, model T1P3002028-SP provides 20 W output power at 1-dB compression across its instantaneous bandwidth of 500 MHz to 2 GHz with 10-dB gain and 50-percent power-added efficiency. For narrowband applications, when tested with a 2-GHz, 100-s pulsed signal at a 10-percent duty cycle +28 VDC with 240 mA quiescent current), it delivers 26 W output power at 1-dB compression with 12 dB gain and 58 percent typical power-added efficiency. The device is rated for minimum gate-to-source breakdown voltage of -40 VDC; the thermal resistance from the device channel to the backside of the carrier is 8.3C/W.
Additional devices include models T13005028-SWP, T1P2701012-SP, and T1P3003028-SP. Model T13005028-SWP is a pulsed depletion-mode pHEMT discrete transistor rated for 50 W output power at 1-dB compression from a +28-VDC supply over its instantaneous bandwidth of 500 MHz to 2 GHz. It achieves linear gain of 10 dB at that output-power level, with 45-percent power-added efficiency. Under narrow band conditions, with a 2-GHz, 100-s pulse at 10-percent duty cycle, and 640 mA quiescent current at +28 VDC, the output power at 1-dB compression increases to 65 W with 12 dB gain and 54 percent power-added efficiency. The device has thermal resistance of +3.5 C/W at +10 VDC and 900 mA quiescent current with max gate-source breakdown voltage of -35 VDC.
Model T1P2701012-SP is a depletion- mode discrete pHEMT device that provides as much as 10 W output power at 1-dB compression over its instantaneous bandwidth of 500 MHz to 3 GHz. At that power level, the linear gain is 10 dB and the power-added efficiency is 50 percent. The maximum gate-source breakdown voltage is -8 VDC. Under narrowband conditions, when tested at 1 GHz with +12 VDC and 200 mA quiescent current, the device achieves 15 W output power at 1-dB compression with 12 dB gain and 60-percent power-added efficiency.
Last, but not least, model T1P-3003028-SP is a depletion-mode pHEMT device that offers 30 W output power at 1-dB compression across its full bandwidth of 500 MHz to 2 GHz. For broadband, instantaneous use, the device features 10 dB linear gain and 45-percent power- added efficiency when operating with 400 mA quiescent current from a +28-VDC supply. The transistor has thermal resistance of 5.6C/W and maximum gate-source breakdown voltage -30 VDC. Under narrowband conditions, when tested with a 2-GHz, 100-s pulsed signal at 10-percent duty cycle and with 400 mA quiescent current at +28 VDC, the transistor delivers 40 W output power at 1-dB compression with 12 -dB gain and 55-percent power-added efficiency.
In addition to the benefits cited from their high efficiency, the generous power offered by these devices over wide instantaneous bandwidths allows circuits and systems to be designed with fewer components and amplifier lineups. The overall cost of the design can be considerably less, resulting in a product with small size and with less power consumed due to the smaller number of highly efficient devices. Another benefit is the reduced inventory to support a number of different frequency bands and amplifiers in production, since PowerBand devices can be used over wide bandwidths. TriQuint Semiconductor, Inc., Colorado Design Center, 2100 Central Ave., Boulder, CO 80301; (720) 406-1221, FAX: (720) 406-1201, e-mail: [email protected], Internet www.triquint.com/powerband.