Multi Stage Switched Sequential Amplifier

This paper presents two and three stage switched sequential amplifiers (SSA) using switched directional couplers as power splitters and combiners. The SSA concept allows matching of the SSA efficiency characteristics to the amplitude probability density distribution of the applied modulated signal. Therefore the back-off efficiency can be increased significantly, e.g. a three stage SSAs can achieve a -10 dB back-off efficiency of more than 50% theoretically. The paper presents the circuit concept for two and three stage SSAs, theoretical considerations for possible efficiency enhancements and experimental results for a two stage SSA.