BY JOHN KELLER

ARLINGTON, Va.-Military radio communications experts at the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., are asking industry for ideas on how to develop an RF transmitter integrated as a monolithic integrated circuit or system-in-package module that relies on a monolithic microwave integrated circuit (MMIC) power amplifier integrated with a dynamic-voltage power supply and control circuit.

Scientists in the DARPA Microsystems Technology Office (MTO) released a broad agency announcement (DARPA-BAA-11-33) for the Microscale Power Conversion (MPC) program to develop a radio transmitter that generates radio signals efficiently through the DC power supply of the transmitter.

Most military RF transmitters today use large, fixed-voltage power converters to supply conditioned power to the semiconductor power amplifier, DARPA officials explain. It is barrier to higher levels of microsystem integration. It is a growing problem, because many of today's military radio systems, as well as those envisioned in the future, use complex modulation techniques with high peak-to-average ratios in signal amplitude. Although the systems are designed for fixed operation at peak condition, power amplifiers often operate well below peak output power much of the time.

To improve the efficient use of power and diverse signal waveforms, DARPA scientists are looking for new envelope tracking or other drain bias modulation techniques to enable RF power supplies to operate far more efficiently by changing the DC voltage that it supplies to the power amplifier rapidly.

The Microscale Power Conversion program seeks to develop POWER ELECTRONICS technology for efficient, very fast supply modulation with high power handling capabilities to make practical use of new RF power amplifier designs. The program seeks to develop a compact, power-efficient RF transmitter by inventing dynamic power conditioning circuits and closely integrating them with RF MMIC power amplifiers and necessary control circuits.

The electrical supply chain from the AC power source to power amplifier supply functions as three lumped stages, officials explain: converting AC power to high-voltage DC power; converting high-voltage DC power to an intermediate DC voltage; and conditioning the resulting power to remove ripple and make subtle adjustments. DARPA is focusing on the final stage by seeking to develop an efficient high-speed power supply modulator to convert input DC voltage rapidly to any DC supply voltage. The key enabling technology will be a fast, low-loss gallium nitride power switch.

MORE INFORMATION IS online at www.fbo.gov/spg/ODA/DARPA/CMO/DARPA-BAA-11-33/listing.html.

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