A Handset Power Amplifier With High Efficiency at a Low Level Using Load-Modulation Technique

摘要

A new monolithic-microwave integrated-circuit power amplifier for cellular handsets has been implemented using the load-modulation concept of the Doherty amplifier, which has a high efficiency at a low power level. In order to get a compact module, the lambda/4 transmission line for the load modulation is replaced by a passive high-pass pi-network, and the load-modulation circuit is also modified to function as a power-matching circuit of the main amplifier. The amplifier has two modes of operation, low- and high-power modes, controlled by a control voltage. At the high power mode, both the main and auxiliary amplifiers are operational and, at the low power mode, only the main amplifier generates output power enhancing the efficiency. For the code-division multiple-access environment, the amplifier at the low-power mode provides power-added efficiency (PAE) of 39.8percent and an adjacent channel power ratio (ACPR) less than 49.8 dBc at 23.1 dBm, and the high-power mode PAE of 37.9percent and ACPR of 46.4 dBc at 28 dBm. The efficiency is improved by approximately 18.8percent at P_(out) velence 23 dBm by the load-modulation technique. For the advanced mobile phone system-mode operation, the amplifier delivers 26.1 dBm with PAE of 53percent and 30.8 dBm with 48.7percent at the low and high modes, respectively.