Inductive Semiconductor Elements and Their Application in Bandpass Amplifiers

Filter circuits using wire-wound inductors are hard to microminiaturize because coils are rather bulky. This paper discusses different inductive semiconductor devices which may replace coils where space is a problem. Forward-biased diodes, properly designed, behave like very lossy inductances. Combining them with negative-resistance devices increases the Q but creates serious temperature and stability problems. Relatively temperature-stable inductance elements are possible by combination of a phase shift network with a transistor. The principle, well-known in tube circuitry, gives high inductances with only a moderate Q because of the low input impedance of the transistor. Promising results have been demonstrated with a transistor operating in the a cutoff region. The device is dc stable, and has a moderate temperature sensitivity which might be partly compensated if necessary. Avalanche multiplication is used to reduce the damping resistance of the inductive transistor. Simple band-pass amplifier circuits are presented in the last section to demonstrate how to use the inductive transistor in practice.