Bandwidth Limitation for the Constant Envelope Components of an OFDM Signal in a LINC Architecture

The linear amplification using non-linear components (LINC) power amplifier architecture uses saturated amplifiers to achieve high efficiency and linearity. However, the non-linear operations for LINC separation lead to bandwidth expansion. The expanded bandwidth causes problems for the analog circuitry and effectively places a limit on the modulation bandwidth of the transmitted signal. We show that for multi-carrier signals, it is the phase component of the transmitted modulation that dominates the spectrum of the LINC components. A novel bandwidth reduction scheme is then proposed for these components. The scheme repetitively limits the bandwidth of the LINC components while inhibiting envelope variations. Measurements show a 46% bandwidth reduction while still meeting the WLAN spectrum mask. This implies an increase of 85% in the modulation bandwidth of the transmitted signal.