Politecnico di Torino - Corso Duca degli Abruzzi, 24 - 10129 Torino, ITALY

+39 011 090 6100 info@tech-share.it

Tunable active inductor with high dynamics

Active filterActive inductorclass ABTunable filter


The invention is an active inductor, that is an electronic circuit that simulates the behavior of an inductance using only active components properly polarized, capabilities and resistances. The value of the equivalent inductance of the circuit in question is electronically variable; the equivalent resistance of the circuit can also be made very low or even negative, and is also electronically adjustable. These characteristics make the circuit suitable for use in tunable filters.

Technical features

The main and innovative feature of the invention in question is the ability to act as an inductance even for high input signal powers, without generating distortion, maintaining the characteristics of tunability and low losses, and with reduced power consumption. This feature allows the design of tunable filters for even relatively high power signals. The above mentioned characteristic is obtained by using as active elements highly linear devices, such as BJT or HEMT, which have a constant gain over a wide range of polarizations; unlike existing circuits, the variability of the inductance value and the adjustability of the parasitic resistance are obtained with appropriate electronically variable passive networks. Moreover, the power dissipation is particularly reduced thanks to the innovative class AB polarization of the active components in “push-pull” configurations, which allows a high linearity even in the presence of a low polarization current. The active inductor can be used with radio frequencies, microwaves and millimetric waves, if made with appropriate technology.

Possible Applications

The patented invention has a number of applications that cover different fields. The main ones can be found below:

  • Analogue electronics;
  • Telecommunications;
  • Radiosurveillance.


  • Low power dissipation in stand by;
  • High signal power that can be managed by the inductor;
  • Tunable values of inductance and resistance series.