A quadrature-modulation EPWM transmitter that uses sine wave carriers for I and Q channel with a 90° hybrid

Quadrature-modulation (QM) envelope-pulse-width modulation (EPWM) transmitter with a 180° hybrid as a power combiner has been proposed to suppress the switching loss due to the breaking of zero-current switching (ZCS) condition and, therefore, to increase the power efficiency. However, we found that the ZCS condition breaking still remains in I-channel of this transmitter. As a result, the power efficiency for I-ch decreases. To solve this problem we propose a QM-EPWM transmitter that uses sine-wave carriers for both I- and Q-channel with a 90° hybrid in this paper. The proposed transmitter eliminates the remaining switching loss due to the phase shift of the carrier in I-channel and increase the power efficiency. The increase in power efficiency of the proposed transmitter from the previous one is evaluated by computer simulation.