In this study, we propose an asymmetrical input transformer for the input baluns in a differential RF CMOS power amplifier to minimize the loss induced by the input transformer. To reduce the loss caused by the magnetic coupling between the primary and secondary parts of a typical transformer, we modify the interconnection between the input transformer and the differential input of the driver stage. Unlike a typical transformer, the primary and secondary parts of the proposed transformer are directly connected to the input of the driver stage. As a result, the input signal in the primary part can reach one of the inputs of the differential driver stage, thereby reducing the loss caused by magnetic coupling. To verify the functionality of the proposed asymmetrical input transformer, we designed a 4.5-GHz differential CMOS power amplifier for IEEE 802.11n WLAN applications with 64-QAM, 9.6 dB PAPR, and a bandwidth of 20 MHz. The designed power amplifier is fabricated using the 180-nm SOI RF CMOS process. The measured maximum linear output power is 17.59 dBm with a gain of 29.23 dB.
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