High Power UltraCMOS Switches and Mixers Satisfy Demanding Military Design Challenges
By Dale Robinette and Mark Schrepferman, Peregrine Semiconductor Corp.

Dramatically revamped several years ago, the Joint Tactical Radio System (JTRS) program looks to be on track to deliver state-of-the-art radio technology for network-centric battlefield applications.1 The road to JTRS systems has been long, and every component in the radio system design must satisfy a list of demanding specifications. In the case of high-power radio frequency (RF) switches and mixers, this list includes exceptional linearity across broad bandwidths in order to avoid RF interference, and this high linearity must be achieved using proven technologies cost effectively and with high reliability.

The demand for this type of wideband device is not exclusive to military radio communications applications, however, because other defense applications, such as radar, missile control, and jammers are all in need of high-power switches. As with all radio designs, be they military or commercial, designers working in these areas must balance performance and reliability with the core constraints of size, power, and cost.

Military Challenges and Applications
JTRS is the military platform designed to encompass all future military radios. It has many incarnations, including ground systems, airborne systems, and specialized radios. For ground applications, devices are needed to support vehicular platforms as well as handheld and manpack systems that require a small radio with low power consumption and high integration. In the airborne domain, systems include airborne and maritime fixed station systems as well as joint and coalition tactical platforms. Specialized radio applications include handheld radios for the Army, Navy, Marine Corps, and Air Force Special Forces.

For JTRS military communications applications, the broadband components that are required typically operate from DC to 2.5 GHz. Some of the manufacturers developing these systems include BAE Systems, Rockwell Collins, Harris, General Dynamics, Viasat and Thales. Other “low-frequency” applications also include improvised explosive device (IED) jammers--systems that can neutralize radio-controlled bombings. Depending on the application, important design concerns also include integration (for size/cost), low insertion loss (for power drain), and high-reliability.

There are other higher-frequency military applications that require operation up to 8.5GHz (X-band). These include missiles (where integration is also important to address size, weight, and cost), radar systems, and space-based applications (where integration, rad-hard qualification, hermetically-sealed packaging, and power consumption are also critical).

UltraCMOS™ Technology Advantages
UltraCMOS Technology, a patented silicon-on-sapphire technology (SOS), has for years been recognized as a technically superior semiconductor material for military and space applications. A major advantage of the UltraCMOS process is that it enables the combination of high-performance RF, mixed-signal, passive elements with nonvolatile memory and digital functions on a single device.

This ability to integrate is driven by CMOS, and it provides for easy integration of different functional blocks, such as the CMOS control function, on the same die as the switch. (Many devices that use other processing technologies must use separate control chips.) Integration directly addresses issues of size, cost, reliability and performance.

CMOS is also very portable, meaning that designs can be easily transferred between wafer fabs, assuring military customers that they have 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 lot-to-lot repeatability as compared to GaAs, which can vary from lot-to-lot and has been known to suffer from passivation issues, which leads to quality concerns.

In terms of performance, the UltraCMOS process offers better linearity than alternative processes; can handle high RF power; delivers broad bandwidth operation, high isolation, low current drain; and is inherently rad-hard for applications that need it. It also offers excellent electrostatic discharge performance and does not require the use of blocking capacitors.
The UltraCMOS process is already in use to manufacture digital step attenuators (DSAs), switches, and mixers for military and space applications.

Switches
For military applications, UltraCMOS high-power switches are available for the lower-frequency applications (DC to 2GHz). These include the PE42510A and PE42650A high power switches from Peregrine Semiconductor. These switches are particularly well suited for transmit receive switching in IED jammers and mobile radios. They can also be used for RF path selection, switching in filter banks, and low noise amplifier (LNA) bypass.

Specifically, the PE42510A and PE42650A feature high power of 50W output power at 1-dB compression (P1dB), typical insertion loss of 0.3dB at 1GHz, high linearity with second and third harmonics of better than -80dBc at 10W, and high ESD resistance of 2kV human body model (HBM) (see Figure 1). Linearity performance is important because it is important to minimize any additional degradation of the signal as it passes through the circuit. In addition to these advantages, the product has low current consumption for prolonged battery life.

For higher-frequency applications, such as a phased array antenna or switch matrix, the UltraCMOS PE95420 supports a broad bandwidth of operation from DC to 8.5 GHz (X-Band)2. Housed in a ceramic package, this monolithic UltraCMOS switch demonstrates industry-leading isolation, low insertion loss, and low current drain. Specifically, the PE95420 offers 82dB isolation at 100MHz, and input third-order intercept point (IIP3) is +60 dBm at 6500MHz, which is an 11dB improvement over competitive devices. Insertion loss is held to 0.8 dB at 100 MHz and 1.7 dB at 8500 MHz, which is a 20% improvement as compared to other available devices. ESD is specified at 2kV HBM.

Mixers
The UltraCMOS process has also been used to design a series of QuadFET mixer core products that allow designers of military and space systems to integrate this high-performance mixer core with other components and IP to make a customized mixer. Because it is UltraCMOS based, the QuadFET core offers very high linearity, low loss and low LO input power which translates into high IIP3.

UltraCMOS technology, with its lack of substrate effects, provides intrinsic advantages for linearity (Figure 2). Specifically, there are no non-linear voltage dependent capacitances (Csb, Cdb, Cgb, for example). The fully insulating sapphire substrate allows for the creation of very high quality factor passives with no voltage coefficients or capacitive substrate coupling. Unlike LTCC-based passives which are plagued with repeatability problems associated with poor control of the shrinking process, UltraCMOS passives enjoy the repeatability of semiconductor processing with inductor tolerances on the order of 2% and capacitor tolerances of 5%. The biasing is internally generated, eliminating the need for external DC-blocking capacitors, and the integrated CMOS decoder reduces the number of required control lines to three and naturally accepts the control levels provided by other CMOS chips.

The PE4150, in particular, also includes a local oscillator (LO) buffer, which allows very high linearity (Figure 3) for a very low LO input signal. This is important because it avoids the need for a high LO signal. (The higher the LO power the more spurious signal power or unwanted signals there are in the radio which could degrade its performance.)

Reliability and Power Handling
UltraCMOS technology offers intrinsic radiation tolerance and high integration, both key factors in high reliability applications. The UltraCMOS high-rel IC products are designed using techniques developed for commercial applications, so power consumption is held to low levels, which is another key factor for high reliability.

In military, instrumentation, industrial and other high temperature applications, a device’s ability to handle high power levels is also important, and it has a direct impact on reliability. In UltraCMOS, the FETs can be stacked in series, which allows for higher voltage handling. Figure 4 shows an example where power handling is measured for +38dBm (17.8 Vpk) across eight UltraCMOS FETs, with DC Vgs of +2.75V. The net result is that each FET handles 2.57 Vpk. By expanding this stacking technique, it is possible to handle up to 10W continuously.

Size, Power, and Cost
As designers balance size, power, and cost, the ability to integrate and use a CMOS-based process offers distinct advantages. For instance, if a designer needed a DSA, switch, and a mixer, they could all be integrated into a single device.

UltraCMOS switches are currently being used to displace PIN diode switches (Figure 5), which typically require up to 20 external components on the printed circuit board. While PIN diode switches offer a lower initial cost, they are not broadband, so they require significant engineering resources to re-band the radio. In addition to size and cost, this type of design approach is also susceptible to quality and reliability issues.

In contrast, an UltraCMOS high-power switch is designed to offer a broad bandwidth. Finally, PIN diode switches consume anywhere from 1 mA to hundreds of mA, while the UltraCMOS switch consumes less than 100 µA, offering a significant advantage in power consumption.
For military applications such as JTRS, design solutions must offer low total application cost and be able to mitigate RF interference. High-power switches and mixers manufactured using UltraCMOS offer the performance, size, and power requirements to satisfy these design needs, and they are already being used to streamline the development process and enhance reliability in mission-critical applications.

Endnotes
1 Robinson, Brian. “JTRS gets back on track,” Defense Systems, Nov 17, 2008.
2 http://www.peregrine-semi.com/articles/2008/2008_pr_11-10(PE95420).pdf

For more information, visit the Peregrine Semiconductor website.

Peregrine Semiconductor Corp.
www.psemi.com
TXTLINX.COM100
Email this article to a friend!