Atkinson, P.; Thomas, P.J.: 'Improved describing function for hysteresis', Electronics Letters, 1975, 11, (7), p. 141-142, DOI: 10.1049/el:19750108
IET Digital Library, https://digital-library.theiet.org/;jsessionid=7c5n6tyw1gq5.x-iet-live-01content/journals/10.1049/el_19750108