3.1 polar antenna impedance detection and tuning for efficiency improvement in a 3G/4G CMOS Power Amplifier

One of the ultimate goals in power amplifier design is to enhance the effective efficiency and achieve a long battery life. Therefore, both the peak efficiency and the efficiency loss due to antenna impedance mismatch or power back-off are highly critical design issues. In particular, the challenge of the antenna impedance mismatch is becoming more severe, due to the increased frequency band and smaller antenna size. Moreover, the antenna mismatch also changes with time due to the user proximity effect [1].