The gyrator is an electric circuit which inverts an impedance. In other words, it can make a capacitive circuit behave inductively, a bandpass filter behave like a band-stop filter, and so on. The concept was invented around 1948 by B.D.H. Tellegen of Philips Research Laboratories, Eindhoven ("The gyrator, a new electric network element", Philips Res. Rep. 3 (1948) pgs 81-101). It is primarily used in active filter design. An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... In electrical engineering, Impedance is a measure of opposition to a sinusoidal electric current. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... A generic band-stop filter, showing both positive and negative angular frequencies In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a range to very low levels. ... An example of high-pass active filter. ...

Simulated inductor

Gyrator simulating Inductance

The primary use of a gyrator is to simulate an inductive element in a small electronic circuit or integrated circuit. Before the invention of the transistor, coils of wire with large inductance might be used in electronic filters. A real inductor can be replaced by a much smaller assembly containing a capacitor, operational amplifiers or transistors, and resistors. This is especially useful in integrated circuit technology. Real capacitors are often much closer to "ideal capacitors" than real inductors are to "ideal inductors". Because of this, a synthetic inductor realized with a gyrator and a capacitor may, for certain applications, be closer to an "ideal inductor" than any real inductor can be. Thus, use of capacitors and gyrators may improve the quality of filter networks that would otherwise be built using inductors. The Q factor of a synthesized inductor can be selected with ease. Image File history File links Gyrator. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which has been manufactured in the surface... Assorted transistors A transistor is a three-terminal semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation, oscillation and many other functions. ... A coil is a series of loops. ... A wire is a single, usually cylindrical, elongated strand of drawn metal. ... Inductance (or electric inductance) is a measure of the amount of magnetic flux produced for a given electric current. ... Television signal splitter consisting of a hi-pass and a low-pass filter. ... Assembly may refer to the following things: In politics, any body meeting together to discuss matters, a parliament or a legislative assembly such as the French revolutionary Legislative Assembly, or a body more designed to mediate between otherwise independent bodies, such as the United Nations General Assembly. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. ... Assorted transistors A transistor is a three-terminal semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation, oscillation and many other functions. ... Resistor symbols (US and Japan) Resistor symbols (Europe, IEC) A pack of resistors A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohms law. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which has been manufactured in the surface... The Q factor or quality factor is a measure of the rate at which a vibrating system dissipates its energy into heat. ...

Operation of the circuit

The circuit works by inverting the effect of the capacitor. The desired effect is an impedance of the form

This is an ideal inductor L with a series resistance R_L. From the diagram, it can be seen that the impedance of the simulated inductor is the desired impedance in parallel with the impedance of C and R.

If R is much greater than R_L, this comes close to

This is the same as a resistance R_L in series with an inductance L = R_LRC. It differs in function from a true inductor due to the parallel RC term, and because R_L is large compared to a real inductor. A real inductor has low internal resistance caused only by the wire it is made of. This limits the Q factor, or accuracy, of filters that can be made with the simulated inductor. The Q factor or quality factor is a measure of the rate at which a vibrating system dissipates its energy into heat. ... Television signal splitter consisting of a hi-pass and a low-pass filter. ...

Applications

The primary application for a gyrator is to reduce the size and cost of a system by removing the need for bulky, heavy and expensive inductors.

Gyrator circuits are extensively used in telephony devices that connect to a POTS system. This has allowed telephones to be much smaller, as the gyrator circuit carries the DC part of the line loop current, allowing the transformer carrying the AC voice signal to be much smaller, due to the massively reduced current. Circuitry in telephone exchanges has also been affected with gyrators being used in SLIC's Plain old telephone service, or POTS, are the services available from analogue telephones prior to the introduction of electronic telephone exchanges into the public switched telephone network. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... A piece of equipment providing central office-like telephone interface functionality. ...

There are many applications where it is not possible to use a gyrator to replace an inductor:

• High Voltage systems (above working voltages of transistors/amplifiers),
• RF systems (RF inductors are usually small anyhow!)

External links

• Good description of this form of the simulated inductor — Elliot Sound Products
• Another description, with the same circuit
• LC filter design using equal value R gyrator, an alternative design
• An alternative circuit
• Another alternative circuit
• Discussion of the gyrator in general and a macro for Micro-Cap V
• Java simulation of this circuit