1kH Synthetic Inductor

Inductors can be mimicked quite easily using operational amplifiers. The circuit shown here was developed to have an inductance of 1000 H (say, one thousand Henry) with good damping. Using this design you can build a resonant circuit with a center frequency of less than 1 Hz. The slow behavior allows you to use conventional measuring instruments to investigate the circuit in real time. The circuit can also be used as part of a filter design. Opamp1 operates as an Integrator, Opamp2 as a difference amplifier.

The output voltage of Opamp2 is equal to the voltage drop across R1 and P1, which is proportional to the output current. This voltage is differentiated by Opamp1, C1 and R2. The net effect is that the circuit behaves as an inductor. P1 allows adjustment of the inductance value. P2 allows adjustment of the Q factor of the coil by altering the symmetry of the difference amplifier and with it the stability of the circuit.