A
gyrator is a
passive, linear, lossless,
two-port electrical
network element proposed in 1948 by
Bernard D. H. Tellegen as a hypothetical fifth
linear element after the
resistor,
capacitor,
inductor and ideal transformer. Unlike the four conventional elements, the gyrator is
non-reciprocal. Gyrators permit
network realizations of two-(or-more)-
port devices which cannot be realized with just the conventional four elements. In particular, gyrators make possible network realizations of
isolators and
circulators. Gyrators do not however change the range of one-port devices that can be realized. Although the gyrator was conceived as a fifth linear element, its adoption makes both the ideal transformer and either the capacitor or inductor redundant. Thus the number of necessary linear elements is in fact reduced to three. Circuits that function as gyrators can be built with transistors and
op amps using
feedback.