electrical network An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sou ...

s, a parasitic impedance is a circuit element ( resistance,

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the ...

capacitance Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...

) which is not desirable in an

electrical component An electronic component is any basic discrete electronic device or physical entity part of an Electronics, electronic system used to affect electrons or their associated electromagnetic field, fields. Electronic components are mostly industrial ...

for its intended purpose. For instance, a

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

is designed to possess resistance, but will also possess unwanted

parasitic capacitance Parasitic capacitance or stray capacitance is the unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors a ...

. Parasitic impedances are unavoidable. All conductors possess resistance and inductance and the principles of duality ensure that where there is inductance, there will also be capacitance. Component designers will strive to minimise parasitic elements but are unable to eliminate them. Discrete components will often have some parasitic values detailed on their datasheets to aid circuit designers in compensating for unwanted effects. The most commonly seen manifestations of parasitic impedances in components are in the parasitic inductance and resistance of the component leads and the parasitic capacitance of the component packaging. For wound components such as

inductor An inductor, also called a coil, choke, or reactor, is a Passivity (engineering), passive two-terminal electronic component, electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typic ...

s and

transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

s, there is additionally the important effect of

that exists between the individual turns of the windings. This winding parasitic capacitance will cause the inductor to act as a resonant circuit at some frequency, known as the ''self-resonant frequency,'' at which point (and all frequencies above) the component is useless as an inductor. Parasitic impedances are often modelled as lumped components in equivalent circuits, but this is not always adequate. For instance, the inter-winding capacitance mentioned above is really a distributed element along the whole length of the winding and not a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

in one particular place. Designers sometimes take advantage of parasitic effects to achieve a desired function in a component, see for instance helical resonator or analog delay line. Nonlinear parasitic elements can also arise. The term is commonly used to describe

parasitic structure In a semiconductor device, a parasitic structure is a portion of the device that resembles in structure some other, simpler semiconductor device, and causes the device to enter an unintended mode of operation when subjected to conditions outside ...

s formed on an

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

whereby an unwanted semiconductor device is formed from p-n junctions which belong to two or more intended devices or functions. The parasitic effects in the

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

of capacitors and parasitic magnetic effects in inductors also include non-linear effects that vary with frequency or voltage and cannot be adequately modelled by linear lumped or distributed components.

References

*John L. Semmlow, ''Circuits, signals, and systems for bioengineers'', pp. 134–135, Academic Press, 2005 . *Steven H. Voldman, ''ESD: Failure Mechanisms and Models'', pp. 13–14, John Wiley and Sons, 2009 {{ISBN, 0-470-51137-0. Electronic design Distributed element circuits