A gyrator is a circuit that uses a couple of capacitors and an amplifier, to simulate an inductor. The circuits reproduced here are the ones commonly used in audio equalizers. The limitation is that one end of the "inductor" is always connected to ground.
Circuit #1 uses an op-amp. The effective inductance is R1*R2*C.
Circuit #2 uses a single transistor. The inductance is R1*R2*C again, but in practice, it will vary a little because the gain of the transistor is not quite unity.
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