A limited bandwidth envelope follower for efficiency enhancement in a linear Power Amplifier in broadband transmitters

An efficiency enhancement scheme for transmitters using a linear power amplifier (PA) for nonconstant amplitude modulation is proposed. Various current and emerging wireless standards require envelope modulation with wide bandwidth. It is difficult to accommodate this in PA supply-modulation schemes using an efficient switched regulator (or S-modulator) to follow the envelope signal, as the regulation efficiency declines with the increase in bandwidth. In the proposed scheme a linear PA is used, having a switched power supply that is modulated with a limited bandwidth, while an amplitude modulated signal, which may be predistorted, is fed to the PA input. The presented real-time signal processing algorithm generates a limited bandwidth power supply modulation signal to minimize the average headroom in the PA, thus increasing its efficiency, while also allowing the switched-regulator to retain high modulation efficiency. Implementation area and power consumption are estimated for 0.18 mum CMOS.