Many existing compact, high-data-rate millimeter-wave wireless communications systems use integrated circuits (ICs) made with gallium arsenide (GaAs) or gallium nitride (GaN). These circuits provide high power and efficiency in small packages but are costly to produce and difficult to integrate with silicon electronics that provide most other radio functions.

Silicon ICs are less expensive to manufacture in volume than those with gallium compounds but until now have not demonstrated sufficient power output and efficiency at millimeter-wave frequencies used for communications and many other military applications, such as radar and guidance systems.

Researchers with DARPA's Efficient Linearized All-Silicon Transmitter ICs (ELASTx) program recently demonstrated an all-silicon, microchip-sized transmitter-a system on a chip (SoC)-that operates at 94 GHz. This accomplishment marks the first time a silicon-only SoC has achieved such a high frequency, which falls in the millimeter-wave range.

"What normally would require multiple circuit boards, separate metal shielded assemblies and numerous I/O cables we can now miniaturize onto one silicon chip about half the size of an adult's thumbnail," said Dev Palmer, DARPA program manager.

"This accomplishment opens the door for co-designing digital CMOS [complementary metal oxide semiconductors] and millimeter-wave capabilities as an integrated system on an all-silicon chip, which should also make possible new design architectures for future military RF systems."

The all-silicon SoC transmitter uses a digitally assisted power amplifier that dynamically adapts amplifier performance characteristics to changing signal requirements. This capability allows for simultaneous optimization of efficiency and linearity-a key goal of all transmitters and power amplifiers designed to quickly deliver large amounts of data on the emerging, net-dependent battlefield.

"This SoC can support a range of modulation formats, so it's possible to communicate to multiple systems using different waveforms from a single silicon chip," Palmer said.

"Its efficient silicon construction will significantly reduce SWAP [size, weight, and power] requirements for millimeter-wave applications, including compact satellite communications ground terminals for frontline troops. These new capabilities will provide connectivity to more service members faster and at lower cost."

The DARPA performer for the all-silicon SoC is Northrop Grumman Aerospace Systems.