The Sky’s the Limit: Silicon-on-Sapphire Processing Takes Flight in Defense and Space Systems
By Dale Robinette, Peregrine Semiconductor Corporation

Since the invention of radios, military and space systems have been early adopters of wireless technology. As commercial use of wireless spectrum increases, however, defense systems must move to higher frequencies in order to increase bandwidth and access clean spectral bands. Because each generation must be smaller, lighter, more robust, and less expensive, wireless systems of all types -- commercial, defense, and space -- have evolved to require increased system complexity with more stringent power budgets.

To meet market requirements, years of research and development have focused on leveraging the low power and ease of integration that is inherent in silicon CMOS technologies to integrate complex RF functions. Relying on advanced CMOS process technologies, system architectures are now based on digital schemes that can often be provided in a single baseband chip for a complex and often multi-standard solution. Because no single semiconductor technology has been able to address these stringent requirements, multi-chip modules (MCMs) have been the preferred approach. Today, however, UltraCMOS™ technology enables wireless system designers to meet all requirements simultaneously in an integrated device. As a silicon CMOS technology, the UltraCMOS process is inherently the lowest power and offers the highest level of integration technology. And, by incorporating a sapphire substrate, UltraCMOS RFICs deliver unprecedented speed with operation up to 13.5GHz.

UltraCMOS™ Technology
UltraCMOS technology combines 100nm thick silicon film and a sapphire substrate, enabling fully depleted CMOS ICs (see Figure 1).

Advantages include:
• Low capacitance, high speed at low power
• Fully depleted operation: improving linearity, speed, and low voltage performance
• Excellent RF performance:
  ° fmax typically 3X ft (100 GHz at 0.25 μm)
  ° very high linearity (+38 dBm IP3 mixers)
  ° high Q integrated passives (QL > 40 at 2 GHz for 5 nH inductor)
  ° high isolation (75 dB at 1 GHz RF switches)
• Integrated EEPROM without additional masks or process steps
• Multiple threshold options without additional cost
• An extremely low-loss substrate at RF frequencies
• Inherent radiation advantages
• Up to 4kV HBM ESD protection with low parasitics
• Processed in standard CMOS facilities; portable and repeatable from fab to fab

UltraCMOS technology enables the integration of high-performance RF, mixed-signal, and passive elements with nonvolatile memory and digital functions on a single device, which in turn drives down size and cost, while improving reliability and performance. CMOS is also very portable, meaning that designs can be easily transferred between wafer fabs, providing aerospace and defense customers with a redundant and constant manufacturing source. In contrast, GaAs wafer fabs tend to differ from one another, making it challenging to port designs between fabs. CMOS processing also is known for excellent manufacturing repeatability as compared to GaAs, which can vary from lot-to-lot and has been known to suffer from passivation issues and quality concerns.

From a performance perspective, the UltraCMOS process offers better linearity than alternative processes, can handle high RF power, delivers broad bandwidth operation, high isolation, low current drain, and has inherent radiation advantages for applications that need it. It also offers excellent electrostatic discharge (ESD) performance. The UltraCMOS process is already in use to manufacture digital step attenuators (DSAs), phase-locked loops (PLLs), prescalers and RF switches for a variety of aerospace and defense applications. In fact, newer UltraCMOS devices operate as high as 13.5GHz to address Ku-Band applications. This capability is of significant interest to the aerospace and defense industries for X and Ku-Band communications and radar applications.

Digital Step Attenuators
A DSA’s attenuation accuracy and switching speed are of particular importance to most RF applications. However, these specifications are of even greater significance in phased array radar applications. The industry has been challenged to increase the speed and accuracy of these applications in order to allow for faster set-up of the antenna to begin scanning or communication.

High-performance DSAs have been recently introduced to the market by Peregrine Semiconductor. These devices provide monotonic attenuation options of 0.25 dB, 0.5 dB, or 1.0 dB steps to 31.75 dB from DC to 6 GHz with best-in-class linearity of +59 dBm input third-order intercept point (IIP3) typical. The product offers an attenuation accuracy of -0.1±0.5 dB at 0 dB to 18 dB attenuation settings DC < 4 GHz (see Figure 2). The DSAs incorporate the flexibility to operate with direct parallel, latched parallel, or serial-addressable programming. UltraCMOS technology has the ability to integrate RF and digital functionality and incorporates a serial addressable feature. This feature permits uniquely addressing up to eight separate DSAs (using addresses 000 – 111) which improves system design flexibility because it eliminates individual control lines. The PE43204 DSA demonstrates a high-speed switching capability of 25ns with output power at 1-dB compression (P1dB) of +30 dBm from 0.05 to 4.0 GHz.

RF Switches
RF switches are being designed into defense applications such as IED jammers and small form-factor radios such as handheld or manpack mobiles. These switches need to include transmit/receive switching and low noise amplifier (LNA) bypass functionality. To perform RF path selection (switching), some designs use filter banks, which typically include multiple PIN diodes per filter leg. Requiring a DC bias, PIN diodes typically run the DC and RF in the same channel, which necessitates additional components to provide proper isolation (see Figure 3).

In an effort to reduce size, weight, and power while increasing performance, the industry is migrating to high-power monolithic switches, such as Peregrine’s PE42510A SPDT and PE42650A SP3T. These small footprint switches (Figure 4) can replace multiple PIN diodes and their supporting circuitry. They also offer high linearity and low IL across a wide bandwidth, thus eliminating significant re-engineering costs associated with re-banding the radio to a different frequency. In the UltraCMOS switch, the RF and DC controls are completely isolated, so the device delivers higher linearity than PIN diodes. In addition, the UltraCMOS process enables stacked FETs, which allow unprecedented high power handling. For example, the PE42510A SPDT and PE42650A SP3T high power RF switches offer 50 W P1dB at an operating frequency of 30 to 2000MHz.

Prescalers
Low power consumption is particularly important for defense applications when soldiers are being equipped with complex electronic systems that are run on battery power. These electronic systems increase not only the capability of the war-fighter but also the weight worn on their backs or packed into ground and air platforms, making it crucial to design for optimized performance and size as well as low power. While UltraCMOS technology provides RF performance competitive with other technologies, it benefits from its CMOS process for ultra-low power consumption. For example, Peregrine’s PE9309 Ku-Band prescaler consumes 1/16th the power of a comparable GaAs device with its 16mA of operating current (41.6 mW of power), replacing higher power competitive GaAs devices that typically consume 600 mW.
The PE9309 prescaler features input power of 0 to +7 dBm, output power of 0 dBm (minimum), and a total dose radiation of 100 Krads (Si). The new prescaler can be used in conjunction with Peregrine’s rad-hard delta-sigma modulated fractional-N PLL frequency synthesizer to generate local oscillator frequencies through the Ku-Band.

Phase Locked Loop
Often determined by the system PLL, phase noise is an important metric for optimal performance. For instance, every ~3 dB improvement in phase noise doubles the data handling capability of the system. Although there are already some impressive PLLs on the market today, phase noise improvement is always a benefit. Peregrine‘s PE97022, PE97042 integer-N, and PE97632 fractional-N PLLs boast a normalized phase noise of -216 dBc/Hz, which is the lowest phase noise of any rad-hard PLL on the market today. Figure 5 demonstrates the performance of a PE97632 UltraCMOS PLL operating in a configuration with Fout = 1.9204GHz, Fcomparison = 20MHz and loop bandwidth = 50 kHz, delivering an exceptional phase noise of -103.81 dBc/Hz at a 10KHz offset.

Integration
Integration is often seen as strategic way to reduce size, weight, and power without tradeoffs in performance. Traditionally, this has meant that the RF, digital, and analog functionality are integrated on separate devices. With UltraCMOS technology, integration of all three of these functions can occur on the same device, offering tremendous advantages that go beyond size, weight, and power. For example, on-chip performance can be greatly improved, and environmental advantages (such as temperature compensation or shock and vibration) can be controlled with a single chip. With the isolation benefits of the sapphire substrate, UltraCMOS designs can integrate mixers, frequency synthesizers, oscillators, switches, prescalers, digital gain control, LNAs, EEPROMs, digital algorithms, and even power amplifiers (PAs). This level of integration is of great interest for applications such as RF front ends or phased array Tx/Rx core control applications.

With superior performance advantages in linearity, isolation, insertion loss, phase noise, high Q integrated passives, low power consumption and ESD protection, the UltraCMOS silicon-on-sapphire process provides the aerospace and defense industry with a wide variety of commonly available commercial, off-the-shelf devices that meet common design challenges. With the ability to integrate RF, digital, and mixed-signal functionality on a single die, UltraCMOS RFICs offer a level of integration that was not previously available to meet next-generation applications. With the increased complexity of multi-band, multi-mode designs for aerospace and defense radio applications, integration is quickly becoming a requirement, and designers will be looking toward technologies like UltraCMOS to take their systems to the next level.

Endnotes
1 Microsemi Corporation, The PIN Diode Circuit Designers’ Handbook, page 6  

Peregrine Semiconductor Corporation
www.psemi.com
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