Integrable, wideband, automatic volume control (a.v.c.) using Pythagoras's law for amplitude detection
F. Doorenbosch, Y. Goinga · Electronics Letters · 1976
The design of an a.v.c. is a simple application of control theory. The main problem in realising an integrable wideband a.v.c. is the amplitude detector. An implementation of Pythagoras's law acts magnificently in a slow a.v.c. However, in a fast a.v.c., offset will cause some 2nd-harmonic distortion.