A switchless reconfigurable transformer CMOS power amplifier

A reconfigurable dual-mode monolithic transformer is presented, which avoids the use of switches for load adaptation. The number of turns of primary winding is varied according to power mode control so that load impedance can be optimized for each operation. The concept of the reconfigurable transformer is demonstrated through the design of a multi-mode power amplifier using bulk CMOS process. Electromagnetic and circuit simulation results validate the operation and performance improvements using the proposed transformer. Low power efficiency at 18dBm is substantially improved from 5.5% to 17.5% using multi-mode control.