1. Maxwell, J. C.: A Treatise On Electricity and Magnetism. Oxford: Clarendon Press (1873) 374–377
2. Haard, E.; Savala, G.: Means for detecting and for generation of pulses. U.S. Patent No.12718621 v. 113.1953, first filed in Sweden March 12 (1952)
3. Cattermole, K. W.: Efficiency and reciprocity in pulse-amplitude modulation: Part 1–Principles. Proceedings of IEE Part B 105 (1958) 449–462
4. Fettweis, A.: Theorie des circuits a transfert resonant. Ph. D. thesis, University of Louvain, Belgium (1963)
5. Fettweis, A.: Theory of resonant-transfer circuits. Lecture Notes, NATO Advanced Study Inst. on Network and Switching Theory: Grignano, Italy Aug. (1966) also published in “Network and Switching Theory’ (ed. G. Biorci) Academie Press: New York (1968) 382–446