Gyrator: Definition from Answers.com Page 1 of 7 Gyrator Sci-Tech Dictionary: gyrator (′jī′rād·ər) (electromagnetism) A waveguide component that uses a ferrite section to give zero phase shift for one direction of propagation and 180° phase shift for the other direction; in other words, it causes a reversal of signal polarity for one direction of propagation but not for the other direction. Also known as microwave gyrator. English▼ Related Videos: Gyrator Gyration Air Mouse - Tech Review Sci-Tech Encyclopedia: Gyrator A linear, passive, two-port electric circuit element whose transmission properties are such that it is effectively a half wavelength longer for one direction of transmission than for the other direction of transmission. Thus a gyrator is a device that causes a reversal of signal polarity for one direction of propagation but not for the other. (A two-port element has apair of input terminals and a pair of output terminals.) This device is novel, since it violates the theorem of reciprocity. See also Reciprocity principle. Until the early 1950s, all known linear passive electrical networks obeyed the theorem of reciprocity. However, several different types of nonreciprocal networks are now widely applied, principally at microwave frequencies. These devices are used to control the direction of signal flow and to protect or isolate components from undesired signals. One common application of a three-port nonreciprocal network, called a circulator, is to permit connection of a transmitter and a receiver to the same antenna. This is accomplished with minimum interference and virtually no power loss of either transmitted or received signal. See also Continuous-wave radar. Perhaps the first passive nonreciprocal system was an optical one proposed by Lord Rayleigh,making use of the rotation of the plane of polarization of light when it passed through a transparent material in the presence of a magnetic field. This phenomenon is called Faraday rotation. http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 2 of 7 The microwave analogy of Lord Rayleigh's device was proposed by C. L. Hogan. The nonreciprocal medium used is fer-rite. In such a material, infinitesimal magnetic dipole moments which arise from the electronic structure of the material act gyroscopically when a steady magneticfield is applied. They precess about the applied field direction in a counterclockwise sense, thus permitting strong coupling to the component of a microwave-frequency magnetic field which is circularly polarized in the same sense. The component with the opposite sense of polarizationis weakly coupled. Thus energy exchange between the magnetic dipoles and the microwave field is polarizationsensitive. See also Ferrimagnetism; Ferrite. Wikipedia: Gyrator A gyrator is a passive, linear, lossless, two-port electrical network element proposed in 1948 by Tellegen as a hypothetical fifth linear element after the resistor, capacitor, inductor and ideal transformer[1]. Unlike the four conventional elements, the gyrator is non-reciprocal. Gyrators permit network realizations of two-(or-more)-port devices which cannot realized with the just the conventional four elements. In particular, [2] gyrators make possible network realizations of isolators and circulators . Gyrators do not however change the range of one-port devices that can be realized. Although the gyrator was conceived as a fifth linear element, its adoption makes both the ideal transformer and either the capacitor or inductor redundant. Thus the number of necessary linear elements is in fact reduced to three. Tellegen's proposed symbol for his gyrator Tellegen invented a circuit symbol for the gyrator and suggested a number of ways in which a practical gyrator might be built. An important property of a gyrator is that it inverts the current-voltage characteristic of an electrical component or network. In the case of linear elements, the impedance is also inverted. In other words, a gyrator can make a capacitive circuit behave inductively, a series LC circuit behave like a parallel LC circuit, and so on. It is primarily used in active filter design and miniaturization. Contents [hide] • 1 Behaviour • 2 Implementation: a simulated inductor ◦ 2.1 Operation ◦ 2.2 Comparison with actual inductors ◦ 2.3 Applications • 3 See also • 4 References • 5 External links http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 3 of 7 Behaviour Gyrator schematic labelled An ideal gyrator is a linear two port device which couples the current on one port to the voltage on the other and vice versa. The instantaneous currents and instantaneous voltages are related by v2 = Ri1 v1 = − Ri2 where is the gyration resistance of the gyrator. The gyration resistance (or equivalently its reciprocal the gyration conductance) has an [3] associated direction indicated by an arrow on the schematic diagram . By convention, the given gyration resistance or conductance relates the voltage on the port at the head of the arrow to the current at its tail. The voltage at the tail of the arrow is related to the current at its head by minus the stated resistance. Reversing the arrow is equivalent to negating the gyration resistance, or to reversing the polarity of either port. Although a gyrator is characterized by its resistance value, it is a lossless component. From the governing equations, the instantaneous power into the gyrator is identically zero. A gyrator is an entirely non-reciprocal device, and hence is represented by antisymmetric impedance and admittance matrices: If the gyration resistance is chosen to be equal to the characteristic impedance of the two ports (or to their geometric mean if these are not the same), then the scattering matrix for the gyrator is which is likewise antisymmetric. This leads to an alternative definition of a gyrator: a device which transmits a signal unchanged in the forward (arrow) direction, but reverses the polarity of the signal travelling in the backward direction (or equivalently, [4] 180° phase-shifts the backward travelling signal ). As with a quarter wave transformer, if one of port of the gyrator is terminated with a linear load, then the other port presents an impedance inversely proportional to that of the load, http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 4 of 7 A generalization of the gyrator is conceivable, in which the forward and backward gyration conductances have different magnitudes, so that the admittance matrix is [5] However this no longer represents a passive device . Implementation: a simulated inductor An example of a gyrator simulating inductance, with an approximate equivalent circuit below. The two Zin have similar values in typical applications. The gyrator network can be used to transform a load capacitance into an 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. An 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. Operation The circuit works by inverting and multiplying the effect of the capacitor in an RC differentiating circuit where the voltage across the resistor behaves through time in the same manner as the voltage across an inductor. The op-amp follower buffers this voltage and applies it back to the input through the resistor RL. The desired effect is an impedance of the form of an ideal inductor L with a series resistance RL: From the diagram, the input impedance of the op-amp circuit is: http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 5 of 7 With RLRC = L, it can be seen that the impedance of the simulated inductor is the desired impedance in parallel with the impedance of the RC circuit. In typical designs, R is chosen to be adequately large that the dominant term is; so, the RC circuit does not impact the input: . This is the same as a resistance RL in series with an inductance L = RLRC. There is a practical limit on the minimum value that RL can take, determined by the current output capability of the op amp. Comparison with actual inductors Simulated elements only imitate actual elements as in fact they are dynamic voltage sources. They cannot replace them in all the possible applications as they do not possess all their unique properties. So, the simulated inductor only mimics some properties of the real inductor. Magnitudes. In typical applications, both the inductance and the resistance of the gyrator are much greater than that of a physical inductor. Gyrators can be used to create inductors from the microhenry range up to the megahenry range. Physical inductors are typically limited to tens of henries, and have parasitic series resistances from hundreds of microhms through the low kilohm range. The parasitic resistance of a gyrator depends on the topology, but with the topology shown, series resistances will typically range from tens of ohms through hundreds of kilohms. Quality. Physical capacitors are often much closer to "ideal capacitors" than physical 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 physical inductor can be. Thus, use of capacitors and gyrators may improve the quality of filter networks that would otherwise be built using inductors. Also, the Q factor of a synthesized inductor can be selected with ease. The Q of an LC filter can be either lower or higher than that of an actual LC filter – for the same frequency, the inductance is much higher, the capacitance much lower, but the resistance also higher. Gyrator inductors typically have higher accuracy than physical inductors, due to the lower cost of precision capacitors than inductors. Energy storage. Simulated inductors do not have the inherent energy storing properties of the real inductors and this limits the possible power applications. The circuit cannot respond like a real inductor to sudden input changes (it does not produce a high-voltage back EMF); its voltage response is limited by the power supply. Since gyrators use active circuits, they only function as a gyrator within the power supply range of the active element. Hence gyrators are usually not very useful for situations requiring simulation of the 'flyback' property of inductors, where a large voltage spike is caused when current is interrupted. A gyrator's transient response is limited by the bandwidth of the active device in the circuit and by the power supply. Grounding. The fact that one side of the simulated inductor is grounded restricts the possible applications (real inductors are floating). This limitation precludes its use in low -pass and notch filters, leaving high-pass and band-pass filters as the only possible applications.[6] 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. For example, RLC http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 6 of 7 bandpass filter characteristics can be realized with capacitors, resistors and operational amplifiers without using inductors. Thus graphic equalizers can be achieved with capacitors, resistors and operational amplifiers without using inductors because of the invention of the gyrator. 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 elimination of DC current through it. Circuitry in telephone exchanges has also been affected with gyrators being used in line cards. Gyrators are also widely used in hi-fi for graphic equalizers, parametric equalizers, discrete bandstop and bandpass filters such as rumble filters), and FM pilot tone filters. There are many applications where it is not possible to use a gyrator to replace an inductor: • High voltage systems utilizing flyback (beyond working voltage of transistors/amplifiers) • RF systems (RF inductors are usually small anyhow) • Power conversion, where a coil is used as energy storage. See also • Negative impedance converter (which can be used to implement a negative inductor with a capacitor) • Sallen–Key topology References 1. ^ B. D. H. Tellegen (April 1948). "The gyrator, a new electric network element". Philips Res. Rep. 3: 81–101. http://techpreservation.dyndns.org/beitman/abpr/newfiles/The%20Gyrator.pdf. Retrieved 2010:03:20. 2. ^ K. M. Adams, E. F. A. Deprettere and J. O. Voorman (1975). Ladislaus Marton. ed. "The gyrator in electronic systems". Advances in Electronics and Electron Physics (Academic Press, Inc.) 37: 79–180. 3. ^ Chua, Leon (unknown), EECS-100 Op Amp Gyrator Circuit Synthesis and Applications, Univ. of Calif. at Berkeley, http://inst.eecs.berkeley.edu/~ee100/fa04/lab/lab10/EE100_Gyrator_Guide.pdf, retrieved May 3, 2010 4. ^ The IEEE Standard Dictionary of Electrical and Electronics terms (6th ed.). IEEE. 1996 [1941]. ISBN 1-55937-833-6. 5. ^ Theodore Deliyannis, Yichuang Sun, J. Kel Fidler, Continuous-time active filter design, pp.81-82, CRC Press, 1999 ISBN 0849325730. 6. ^ An audio circuit collection, Part 3 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 Webarchive backup: Another alternative circuit Discussion of the gyrator in general and a macro for Micro-Cap V Java simulation of this circuit http://www.answers.com/topic/gyrator 6/1/2010 Gyrator: Definition from Answers.com Page 7 of 7 • Single transistor gyrator for telephony applications • SPICE Analysis of gyrator for telephony applications • Negative floating inductor with only 2 Op-amps Article here This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer) Donate to Wikimedia Related topics: gyrator filter (electronics) ferrite rotator (electromagnetism) gyrate Related answers: What is meant by Radius of gyration? Read answer... Can you make a sentence with the word gyration? Read answer... Is radius of gyration depend on mass? Read answer... Help us answer these: What is redius of gyration? What is angle of gyration? What is Gyrational force? Post a question - any question - to the http://www.answers.com/topic/gyrator WikiAnswers community: 6/1/2010