Basic considerations and topologies of switched-mode assisted linear power amplifiers

• Published in: Proceedings of Applied Power Electronics Conference. APEC '96 Vol. 1; pp. 207 - 213 vol.1
• Main Authors: Ertl, H., Kolar, J.W., Zach, F.C.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 1996
• Subjects: Delay; Feedback loop; High power amplifiers; Master-slave; Power amplifiers; Power harmonic filters; Power transistors; Switching frequency; Topology; Transient response
• ISBN: 0780330447; 9780780330443
• DOI: 10.1109/APEC.1996.500444

The paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers-the high loss-is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multi-stage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given.