viernes, 23 de julio de 2010
Technological advances lead to tactical advantages. That's why investments in electronic technology for military applications traditionally run high. Yet those investments can often yield useful breakthroughs as well as dramatic improvements in existing technologies.
Military systems such as electronic warfare (EW), signal intelligence (SIGINT), and radar systems receive the most funding. Still, electronic building blocks such as amplifiers, display screens, software, and transistors enable those large systems and, hopefully, provide that tactical edge.
One of the most basic electronic building blocks is the transistor. Military system designers have long sought more power from a single device to achieve higher power densities in radar and EW transmitters for a given size. Two of the more significant developments in silicon transistor technology come from companies at the extremes of the supply curve: Freescale Semiconductor and HVVi Semiconductors. The former applies a traditional lateral silicon device architecture, while the latter employs a unique vertical configuration in its novel silicon transistors.
A CLOSER LOOK
Freescale is well established for its laterally diffused metal-oxide-semiconductor (LDMOS) devices, especially for cellular basestations and other commercial comms systems. By extending its LDMOS process capabilities to 50-V transistor fabrication, it developed its model MRF6V14300H transistor for pulsed military systems, including radar and avionics systems (Fig. 1).
The Si LDMOS transistor is one of the first fruits of Freescale's sixth-generation Very High Voltage (VHV6) process. VHV6 is an evolution of the LDMOS process used to manufacture +28-V dc parts for commercial broadcast, communications, industrial, and medical applications, along with some military systems.
By operating at the higher bias voltage while maintaining good thermal dissipation, the MRF6V14300H can deliver 330-W peak output power with 17-dB power gain from 1200 to 1400 MHz. The output power is based on pulsed input signals with 300-µs pulse width with 12% duty cycle. Under those conditions, the transistor achieves 60% drain efficiency.
Taking a more unconventional approach, HVVi uses a vertical transistor architecture to obtain higher power levels at high frequencies, but also relies on a high supply voltage of +48 V dc. The company's patented high-voltage vertical field-effect-transistor (HVVFET) technology employs the transistor's foundation or substrate as the device drain.
The transistor depletes vertically into the substrate as the supply voltage is fed to the drain. It approaches planar breakdown in the vertical drain region, standing off maximum voltage with minimum on resistance. The technology forms the basis for the company's first three products, designed for high-power pulsed applications at L-band frequencies— Identify Friend or Foe (IFF), TCAS, TACAN, and Mode-S radar systems.
The lower-frequency PVV1011-300 HVVFET transistor is designed for 300-W pulsed output power from 1030 to 1090 MHz. It achieves that output level with 15-dB power gain and 48% drain efficiency when operating with 50-µs pulse-width input signals for a 1-ms pulse period.
The PVV1214-25 and PVV1214-100 HVVFETs provide higher frequency. The former delivers a 25-W output level from 1200 to 1400 MHz. The latter is rated for 100-W output power from 1200 to 1400 MHz. Both are characterized with 200-µs pulse-width input signals at a 10% pulse duty cycle.
Building on the HVVFET technology, HVVi has added a trio of transistors for airborne distance-measuring-equipment (DME) systems in the 1025- to 1150-MHz range. The HVV1012-060, HVV1012-100, and HVV1012-250 are designed for use with pulsed L-band signals. All three have been characterized with a +48-V dc supply and with 10-µs pulse-width signals at 1% duty cycle.
In spite of the novel architecture, these L-band power transistors are based on conventional silicon substrate materials, typically relying on multiple transistor cells in a push-pull configuration to achieve high output-power levels. Some transistor suppliers, such as Microsemi, have sought out more exotic device materials for higher transistor power, including silicon carbide (SiC) with its outstanding thermal properties, to dissipate the heat generated by the active device cells.
Microsemi's 0150SC-1250M and 0405SC-1000M RF power transistors are SiC-based static-induction transistors (SITs), single-ended designs with very simple impedance-matching requirements compared to typical silicon bipolar or LDMOS transistors. The Class AB transistors are about half the size of equivalent-power LDMOS or bipolar transistors.
The 0150SC-1250M typically provides 1400-W pulsed output power in the very high-frequency (VHF) band from 150 to 160 MHz. The 0405SC-1000M typically delivers 1100-W pulsed output power in the ultra-high-frequency (UHF) band from 406 to 450 MHz.
The SiC transistors are housed in single- ended flange-mount power packages, assembled with 100% gold metallization and gold wire bonds in hermetic packages for the highest reliability in hostile environments. They are ideal for solid-state power amplifiers for VHF weather radar and long-range tracking radar systems.
Several oscillator/synthesizer products represented significant advances in signal-generation technology for military electronics systems. The VMEM5Q military clock oscillator from Vectron International builds on microelectromechanical- systems (MEMS) technology to provide the performance needed in the high-shock and high-vibration environments of military systems (Fig. 2). The clock oscillators, which can be specified with CMOS-compatible outputs at frequencies from 1 to 130 MHz, suit a wide range of military electronics applications, including smart munitions, missiles, and projectile electronics.
The rugged VMEM5Q oscillators withstand shock levels to 100,000 g. Qualification testing of a 125-MHz unit showed no degradation in performance at the maximum capabilities of the shock/ vibration test set, 30,000 g in each axis. They integrate PureSilicon Resonator MEMS resonators from Discera and feature CMOS-level output signals with typical rise/fall time of 5 ns with typical period jitter of only 7 ps.
For enhanced stability, the VMEM5Q oscillators include temperature compensation. They come in RoHS-compliant (Restrictions on Hazardous Substances) 5- by 3.2-mm quad flat no-lead (QFN) surface-mount packages and undergo extensive qualifications testing, including to MIL-PRF-55310 requirements.
Generating signals with a greater level of integration, the WaveCor SLO 2.0 source from the Microwave Systems division of ITT Corp. offers a frequency range of 50 MHz to 20.48 GHz based on direct-digital synthesis (DDS). With this technology, digital codes are converted to analog waveforms via digital-to-analog converters (DACs) and then upconverted in frequency, filtered, and amplified to reach a final required output range.
The WaveCor SLO 2.0 packs all of these functions into 6.00 by 6.00 by 2.75 in., weighing less than 5 lb. The compact DDS source tunes across that wide frequency range with 1-kHz resolution. Suitable for EW, radar, SIGINT, and automatic-test-equipment (ATE) systems, the device provides +14-dBm output power with ±1-dB flatness. It achieves low phase noise of -126 dBc/Hz measured at an offset of 10 kHz from a 10-GHz carrier signal.
DSP technology for military systems is also found within digital RF memory (DRFM), which captures continuouswave (CW) and pulsed threat signals for analysis. Essential components in many electronic-countermeasures (ECM) systems, DRFMs typically include a highspeed analog-to-digital converter (ADC) to transform analog inputs into digital code and a high-speed DAC to make the conversion back to analog signals.
A 10-bit DRFM from KOR Electronics is an integral part of several electronic- control module systems, available with as much as 1-GHz instantaneous capture bandwidth. Its high-resolution digitizing function is supported by a 12-bit DAC at the output port for high signal resolution and linearity.
Once a system captures signals, they still must be processed and displayed into meaningful results. UniPixel has made impressive improvements in color displays through its Time Multiplexed Optical Shutter (TMOS) technology. With TMOS, a single color source produces extremely short bursts of color, emitted so quickly that the eye combines the bursts as one color. The technique, known as "spatial additive color," uses different durations of blue, red, and green to create a variety of shades and hues.
Compared to plasma or LCD color screens, UniPixel displays require few layers, making them relatively less expensive to manufacture than conventional displays and with potentially greater reliability because of their simplicity. Prototype displays based on the technology have employed thin-film-transistor (TFT) structures and required only 12-V operating voltage with performance of 150 frames/second or better.
Military training has long depended on simulation software and hardware that depicts images in two dimensions, not drastically different than many video games. But two companies, EffectiveUI and Intelligence Gaming, intend to transform military simulations into realistic, 3D training exercises.
With the firms' RealityV video technology, users wear a head-mounted display and enter a lifelike, 360° video and sound simulated scenario that provides realistic simulation and training. The display gives a trainee realistic renditions of live action scenarios, as well as a taste of hostile situations. RealityV collects specific psychometric data during an exercise to determine a "player's" ability to handle new challenges and changing situations.
When it comes time to provide content for a military simulation, the Hurricane surveillance camera from Electrophysics Corp. can capture images during day or night. It combines a charge-coupleddevice (CCD) camera for daytime viewing with thermal imaging electronics for night-vision capabilities.
During the day, it provides about 630,000-pixel resolution in NTSC format and 740,000-pixel resolution in PAL format. At night, it can detect human signatures at distances of 2 km or more. It includes a vehicle mount and is tested to MIL-STD-810E requirements.
Freddy Vallenilla Roa. CAF
Publicado por Tecnología en Telecomunicaciones - conocimientos.com.ve en 17:04
Etiquetas: 1II 2010-1 CAF Freddy Vallenilla