A unique current-controlled negative resistance generator

THE PHENOMENON of negative resistance is so well known that it requires only a cursory review. Negative resistance elements or networks are distinguished by driving-point resistance characteristics which exhibit, at least over a limited portion of the current-voltage (i-v) plane, a falling voltage with increasing current. In general, devices which exhibit a negative resistance region over some portion of their i-v characteristic curve may be separated into two classes. The first class includes all elements with an inherent negative resistance region, such as the point-contact transistor, unijunction transistor, p-n-p-n transistor, tetrode vacuum tube, and tunnel diode. The second class includes all the networks in which one or more active elements are used in conjunction with passive elements arranged to maintain a predetermined function of current and voltage. This group includes all the devices which may be synthesized by utilizing positive feedback and such circuits as the complementary transistor cascade and the negative impedance converter. It should be understood that a physically realizable negative resistance is not the opposite of a positive resistance. For a positive resistance, the i-v relationship is an interdependent one, but for a negative resistance, the element utilizes an internal phenomenon which depends only on the potential or only on the current. Therefore, a 2-terminal negative resistance device comprises an internal energy source which is controlled either by the current through or the potential across its terminals, but not by both.