Power Spectral Analysis of the Envelope Pulse-Width Modulation (EPWM) Transmitter for High Efficiency Amplification of OFDM Signals

Multi-carrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) require linear amplification and have low power efficiency because of high peak-to-average power ratio (PAPR). In an Envelope Pulse-Width Modulation (EPWM) transmitter, the envelope component of a linear modulation wave is converted to a PWM signal by a delta-sigma (Delta-Sigma) modulator while the phase component modulates the carrier signal. The distortion-free amplitude multiplexing of the PWM and PM signals enables the power amplifier to achieve maximum power efficiency. In this paper, EPWM transmitter characteristics such as noise power spectral density and SNR will be analyzed. The application of the EPWM transmitter to OFDM signals will also be explored. From the simulation results, the Delta-Sigma modulator with an oversampling ratio of 32 provides sufficient in-band SNR and adjacent channel power ratio required for the IEEE 802.11a OFDM system.