Multiple-state, switch-mode power amplifier systems and methods of their operation

An embodiment of an amplifier includes N ( N> 1) switch-mode power amplifier (SMPA) branches. Each SMPA branch includes two drive signal inputs and one SMPA branch output. A module coupled to the amplifier samples an input RF signal, and produces combinations of drive signals based on the samples. When an SMPA branch receives a first combination of drive signals, it produces an output signal at one voltage level. Conversely, when the SMPA branch receives a different second combination of drive signals, it produces the output signal at another voltage level. At least two of the SMPA branches produce output signals having different absolute magnitudes. A combiner combines the output signals from all of the SMPA branches to produce a combined output signal that may have, at any given time, one of 2* N +1 quantization states.