The regenerative circuit (or regen) allows an electronic signal to be amplified many times by the same active device. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback loop, providing positive feedback. This circuit was widely used in radio receivers, called regenerative receivers, between 1915 and World War II. The regenerative receiver was invented in 1912 and patented in 1914 by American electrical engineer Edwin Armstrong when he was an undergraduate at Columbia University. Due partly to its tendency to radiate interference, by the 1930s the regenerative receiver was superseded by other receiver designs, the TRF and superheterodyne receivers and became obsolete, but regeneration (now called positive feedback) is widely used in other areas of electronics, such as in oscillators and active filters.