Power-supply modulation steps up handset-power-amp efficiency

RF-engineering company Nujira has extended the reach of its efficiency-boosting technology for power amplifiers into the handset. The company has until now focused on the infrastructure side of communications, selling its HAT (high-accuracy-tracking) power-line modulators into applications such as base stations.

The fundamental principle is that RF power amps—especially those for modern digital-modulation schemes, such as 3 and 4G (third- and fourth-generation) LTE (long-term evolution) and WiMax (worldwide interoperability for microwave access)—must be linear; that is, they must operate from a fixed-voltage rail. When modulation levels are low, a great deal of the power in the output stage contributes nothing to the output; therefore, efficiency is low.

HAT modulates the power rail to the power amp in step with the RF-waveform envelope, reducing losses. Nujira has now applied the principles of HAT to an IP (intellectual-property) business model and aims to sell the same concept, which it brands as Coolteq-I, into handsets. Thus equipped, a handset power amplifier could be twice as efficient when transmitting an HSUPA (high-speed-uplink-packet-access) waveform and as much as four times as efficient for WiMax. Licensees will implement Coolteq-I IP in the power regulator for the power amp and in the baseband chip set to derive the envelope signal.

In hardware terms, the implementation should be cost-neutral because it replaces an existing regulator, and the added gate count in the baseband is almost trivial. As well as improving efficiency, the technology will assist the architecture shift necessary for reducing multiple power amps for different bands into—typically—two wideband amplifiers.

Depending on operating conditions and traffic type—and especially with data traffic exhibiting high peak-average-ratio values—terminal-battery life might improve by as much as 30% due to Coolteq-I alone, Nujira believes. The company will deliver the IP in a conventional fee-plus-royalty model, as a set of design libraries and procedures, with supporting models, an evaluation kit, and a suitable power-amplifier design.