Coding efficiency for different switched-mode RF transmitter architectures

Conventional RF transmitters with power amplifiers in e.g. Class-AB operation provide only moderate electrical efficiencies for complex modulated signals. To increase the overall efficiency considerably, we can employ switched-mode power amplifiers (SMPA) with an appropriate baseband signal processing. Such efficient SMPAs generate a lot of spectral out-of-band components, which has to be attenuated by a bandpass filter before the signal is fed to the transmit antenna. Unfortunately, this impacts the electrical efficiency because these unwanted signal components are usually dissipated within the transmitter. A measure for the electrical efficiency degradation for complex modulated signals in a switched-mode operation is the coding efficiency. In this paper we develop different switched-mode transmitter architectures based on baseband PWM coding and analyze the coding efficiencies for different signal statistics.