The gyrator - or simulated inductor - is a valuable component for use in low-frequency electronic filters. It is economical, and offers potentially excellent performance over a frequency range where conventional inductors are difficult to realise.

Unfortunately, the conventional circuit configuration, involving two 'nose-to-tail' operational amplifiers, is very susceptible to high-frequency oscillations. This report analyses the circuit in detail, and proposes a modification to overcome the problem.

The BBC has been granted a patent, GB2365235, for the modification.