System-Efficiency Analysis of Power Amplifier Supply-Tracking Regimes in Mobile Transmitters

Maintaining high RF efficiency in the transmitters of mobile phones is becoming more difficult as data rates rise with increasing modulation complexity and crest factor. In addressing the problem, it is critical for commercial suppliers of system solutions for mobile phones to understand exactly what gains can be achieved by the various options available before investing time, money and resources. This paper presents a comprehensive system analysis of the total efficiency gains achievable in the RF parts of a multimode transmitter that arise from adding a hybrid modulator between the battery and supply terminal of the power amplifier (PA). Behavioral modeling is used to simulate the modulator, the PA and the combination of the two under various envelope-tracking and polar-modulation regimes. The results are supported by measured data. They indicate that PA efficiency for EDGE and UMTS modes can be improved by as much as 20%, although this is easily negated by losses in the modulator.