of Switching-Mode Class-E Techniques TH1D-2: Nathan Sokal and the Class-E Amplifier Early History of Switching-Mode Class-E Techniques for High-Efficiency Power Amplification Andrei Grebennikov Sumitomo Electric Europe 220 Centennial Park, Elstree, Hertfordshire, UK

of Switching-Mode Class-E Techniques Early History of Switching-Mode Class-E Techniques for High-Efficiency Power Amplification Late 1940s – early 1960s Mid-1960s Late 1960s – early 1970s Early-mid 1970s (Sokals)

Early history of Class-E techniques: late 1940s – early 1960s Late 1940s – early 1950s: first observations of efficiency increase during experimental tuning of vacuum-tube amplifiers in saturation mode Conclusion: detuning of resonant circuit must be provided in direction of higher frequencies when operating frequency is lower than resonance frequency of resonant circuit: inductive impedance for fundamental capacitive impedances for higher-order harmonics resulting anode voltage fundamental anode voltage second-harmonic anode voltage third-harmonic anode voltage A. G. Khvilivitsky, “Designing the vacuum-tube generator, operating on detuned load (in Russian),” Radiotekhnika, vol. 8, pp. 21-26, Apr. 1953.

Early history of Class-E techniques: late 1940s – early 1960s Loss in tube at optimal detuning Lopt Loss in tube at resonance Load phase angle of 30-40 by varying inductance Efficiency of 92-93% up to 3 MHz E. P. Khmelnitsky, “A new concept of significant increasing of fundamental power and efficiency of generator, operating in saturation mode (in Russian),” Radiotekhnika, vol. 10, pp. 59-63, Aug. 1955. E. P. Khmelnitsky, Operation of Vacuum-Tube Generator on Detuned Resonant Circuit (in Russian), Moskva: Svyazizdat, 1962.

Early history of Class-E techniques: late 1940s – early 1960s conduction angle phase shift Load network with series capacitance and parallel filter 35 inductive impedance at fundamental R. G. de Buda, “Design equations for a new class of amplifier,” Report RQ62EE5, Canadian General Electric: Technical Information Series, Feb. 1962.

Early history of Class-E techniques: mid-1960s Load network with shunt capacitance and series filter Efficiency of 94% at 500 kHz G. D. Ewing, High-Efficiency Radio-Frequency Power Amplifiers, Ph.D. Dissertation, Oregon State University, June 1964.

Early history of Class-E techniques: mid-1960s 69 MHz Ideal switch represents transistor Load network with shunt capacitance and series filter Efficiency up to 85% from 48 to 70 MHz One set of linear first-order differential equations describes OFF condition, another set is used for ON state without assumption of zero voltage derivative: approximate solution D. R. Lohrmann, “Amplifiers has 85% efficiency while providing up to 10 watts power over a wide frequency band,” Electronic Design, vol. 14, no.10, pp. 38-43, Mar. 1966.

Early history of Class-E techniques: mid-1960s Parallel resonant circuit has resonance frequency equal to about 1.5 times carrier frequency: - inductive impedance at carrier frequency - capacitive reactances at high-order harmonics Efficiency of 89% at 3.2 MHz J. W. Wood, “High efficiency Class C amplifier,” U.S. Patent 3,430,157, Feb. 1969 (filed Nov. 1966).

Early history of Class-E techniques: late 1960s – early 1970s One set of linear first-order differential equations describes OFF condition, another set is used to describe ON state: zero voltage and zero voltage derivative at turn-on instant Load network with shunt capacitance and series inductance A. D. Artym, “Switching-mode operation of high-frequency generators (in Russian),” Radioteknika, vol. 24, pp. 58-64, June 1969 A. D. Artym, “Switching-mode operation of high-frequency generators,” Telecommunications and Radio Engineering, part 2, vol. 24, pp. 99-104, June 1969

Early history of Class-E techniques: late 1960s – early 1970s q = 1/ LC = 2 Sinusoidal load current Second-order differential equation for voltage across shunt capacitance C Load network with shunt capacitance, series inductance and shunt filter A. D. Artym, “Switching-mode operation of high-frequency generators (in Russian),” Radioteknika, vol. 24, pp. 58-64, June 1969 A. D. Artym, “Switching-mode operation of high-frequency generators,” Telecommunications and Radio Engineering, part 2, vol. 24, pp. 99-104, June 1969

Early history of Class-E techniques: late 1960s – early 1970s For duty ratio - dc-supply voltage - output power at f0 V. V. Gruzdev, “Toward calculation of contour parameters of single-ended switching-mode generator (in Russian),” Trudy MEIS, vol. 2, pp. 124-128, 1969.

Early history of Class-E techniques: late 1960s – early 1970s Loss due to finite switching time: Loss due to saturation resistance: I. A. Popov, “Switching mode of single-ended transistor generator (in Russian),” Poluprovodnikovye Pribory v Tekhnike Elektrosvyazi, vol. 5, pp. 15-35, 1970.

Early history of Class-E techniques: late 1960s – early 1970s Load network with shunt capacitance and series inductance V. B. Kozyrev, “Single-ended switching-mode generator with filtering contour (in Russian),” Poluprovodnikovye Pribory v Tekhnike Elektrosvyazi, vol. 8, pp. 152-166, 1971.

Early history of Class-E techniques: late 1960s – early 1970s Load network with parallel circuit V. B. Kozyrev, “Single-ended switching-mode generator with filtering contour (in Russian),” Poluprovodnikovye Pribory v Tekhnike Elektrosvyazi, vol. 8, pp. 152-166, 1971.

Early history of Class-E techniques: late 1960s – early 1970s Zero voltage-derivative condition becomes equivalent to zero current-derivative condition Loss due to finite switching time: 1% (a = 0.35 or 20) Loss due to saturation resistance: Peak switch voltage: >20% for  = 180 (or 50% duty ratio) 1.5-2 times for  > 210 V. B. Kozyrev, “Single-ended switching-mode generator with filtering contour (in Russian),” Poluprovodnikovye Pribory v Tekhnike Elektrosvyazi, vol. 8, pp. 152-166, 1971.

Early history of Class-E techniques: early-mid 1970s (Sokals) N. O. Sokal and A. D. Sokal, "Optimal design for efficiency of tuned single-ended switching power amplifiers," Proceedings of 1972 IEEE International Symposium on Circuit Theory, p. 389.

Early history of Class-E techniques: early-mid 1970s (Sokals) Class E with shunt capacitance and series filter N. O. Sokal and A. D. Sokal, "Class E  A new class of high-efficiency tuned single-ended switching power amplifiers,” IEEE J. Solid-State Circuits, vol. SC-10, pp. 168-176, June 1975.

Early history of Class-E techniques: early-mid 1970s (Sokals) N. O. Sokal and F. H. Raab, “Harmonic output of Class-E RF power amplifiers and load coupling network design,” IEEE J. Solid-State Circuits, vol. SC-12, pp. 86-88, Feb. 1977 N. O. Sokal and A. D. Sokal, “High-efficiency tuned switching power amplifier,” U.S. Patent 3,919,656, Nov. 1975 (filed Apr. 1973). N. O. Sokal, “Class E can boost the efficiency of rf power amplifiers, and keep transistors cool and reliable,” Electronic Design, vol. 25, pp. 96-102, Sep. 1977

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