1. 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

2. 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)

3. 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 , Apr

4. 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 , Aug
E. P. Khmelnitsky, Operation of
Vacuum-Tube Generator on Detuned Resonant Circuit (in Russian),
Moskva: Svyazizdat, 1962.

5. 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

6. 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.

7. 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 , Mar

8. 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 (filed Nov. 1966).

9. 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 , June 1969
A. D. Artym, “Switching-mode operation of high-frequency generators,” Telecommunications and Radio Engineering, part 2, vol. 24, pp , June 1969

10. 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 , June 1969
A. D. Artym, “Switching-mode operation of high-frequency generators,” Telecommunications and Radio Engineering, part 2, vol. 24, pp , June 1969

11. 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 , 1969.

12. 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 , 1970.

13. 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 , 1971.

14. 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 , 1971.

15. 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 , 1971.

16. 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.

17. 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 , June 1975.

18. 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 , Feb. 1977
N. O. Sokal and A. D. Sokal, “High-efficiency tuned switching power amplifier,” U.S. Patent 3,919,656, Nov (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 , Sep. 1977

19. Nathan Sokal and the Class-E Amplifier
Ukraine
Poland