Abstract
A CMOS power amplifier integrated circuit with an optimized dual-mode supply modulator is presented. The dual-mode supply modulator, based on a hybrid buck converter consisting of a wideband linear amplifier and a highly efficient switching amplifier, provides two operation modes: envelope tracking (ET) for high average output power and average power tracking (APT) for low output power. For the APT mode, the linear amplifier is switched off and the switching amplifier operates as a normal buck converter to supply DC voltage to the power amplifier according to the average output power. The optimum switch sizes of the switching amplifier were analyzed and applied for each operation mode for higher efficiency. An integrated circuit with a power amplifier and the dual-mode supply modulator was designed and fabricated using a 0.18- $\mu\mbox{m}$ CMOS process for LTE applications at a frequency of 0.78 GHz. For the 16-QAM uplink LTE signal, the measured efficiency with an ET mode is as high as 45.4%, which is 7.0% higher than that from the stand-alone power amplifier at an average output power of 24 dBm. An efficiency of 14.1% was achieved with an APT mode at an average output power of 9 dBm. This is 3.2% higher than that with the ET mode.
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