Contents I. INTRODUCTION
Recently, some kinds of high efficiency and low distortion technology for power amplifier are proposed. Especially, efficiency of power amplifier can be improved by using envelope-tracking (ET) technique, envelope elimination and restoration (EER) technique and dynamic bias method [1][3]. In such as technique, digital control methods are usually performed by DSP. The digital control methods use the baseband signal such as in-phase (I) and quadrature (Q) IF signals, which are converted RF signal after A-D converter. These IQ signals include amplitude and phase information of RF signal, respectively. Moreover, up-converted RF signal includes envelope signal as well as IQ signals. In such as the EER system, because the supply voltage is modulated by the envelope signal which is amplified by envelope amplifier, the power amplifier can keep operating close to saturated power to improve efficiency. However, distortion and efficiency characteristics of power amplifier strongly depend on amplitude balance and timing of these IQ singles. The timing difference of IQ signals significantly deteriorates distortion characteristics. Moreover, the power dissipation of the envelope amplifier the EER system reasonably large. And, digital control method, very fast A-D converter needed under wide frequency range such as over several ten-MHz, and power consumption of the A-D converter also dramatically increases.
