Electrical Engineering Dictionary, Notas de estudo de Engenharia Elétrica

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“Book/Definitions”

Electrical Engineering Dictionary.

Ed. Phillip A. Laplante

Boca Raton: CRC Press LLC, 2000

Special

Symbols

α -level set a crisp set of elements belong- ing to a fuzzy set A at least to a degree α

Aα = {x ∈ X | μA (x) ≥ α}

See also crisp set, fuzzy set.

1f common symbol for bandwidth, in hertz.

 rGaAs common symbol for gallium ar- senide relative dielectric constant.  rGaAs = 12 .8.

 rSi common symbol for silicon relative dielectric constant.  rSi = 11 .8.

 0 symbol for permitivity of free space.  0 = 8. 849 × 10 −^12 farad/meter.

 (^) r common symbol for relative dielectric constant.

η DC common symbol for DC to RF con- version efficiency. Expressed as a percent- age.

η (^) a common symbol for power added ef- ficiency. Expressed as a percentage.

η (^) t common symbol for total or true effi- ciency. Expressed as a percentage.

(^0) opt common symbol for source reflec- tion coefficient for optimum noise perfor- mance.

μ 0 common symbol for permeability of free space constant. μ 0 = 1. 257 × 10 −^16 henrys/meter.

μ (^) r common symbol for relative perme- ability.

ω common symbol for radian frequency in radians/second. ω = 2 · π · frequency.

θ+ common symbol for positive transition angle in degrees.

θ− common symbol for negative transi- tion angle in degrees.

θ cond common symbol for conduction an- gle in degrees.

θ sat common symbol for saturation angle in degrees.

θ (^) CC common symbol for FET channel- to-case thermal resistance in ◦C/watt.

θ (^) J C common symbol for bipolar junction- to-case thermal resistance in ◦C/watt.

A∗^ common symbol for Richardson’s constant. A∗^ = 8 .7 amperes · cm/◦K

BV (^) GD See gate-to-drain breakdown voltage.

BV (^) GS See gate-to-source breakdown voltage.

dv/dt rate of change of voltage with- stand capability without spurious turn-on of the device.

H (^) ci See intrinsic coercive force.

n (^) e common symbol for excess noise in watts.

n (^) s h common symbol for shot noise in watts.

mean any pair X ∈ R p×m^ [s], Y ∈ R q×m^ [s] satisfying the equation. The equation (1) has a solution if and only if the matrices [A, B, C] and [A, B, 0] are column equiva- lent or the greatest common left divisor of A and B is a left divisor of C. The 2-D equation

AX + Y B = C ( 2 )

A ∈ R k×p^ [s], B ∈ R q×m^ [s], C ∈ R k×m^ [s] are given, is called the bilateral 2-D polyno- mial matrix equation. By a solution to (2) we mean any pair X ∈ R p×m^ [s], Y ∈ R k×q^ [s] satisfying the equation. The equation has a solution if and only if the matrices [ A 0 0 B

]

and

[

A C

0 B

]

are equivalent.

2-D Roesser model a 2-D model de- scribed by the equations [ x (^) ih+ 1 ,j x (^) i,jv + 1

]

[

A 1 A 2

A 3 A 4

] [^

x hij x vij

]

[

B 1

B 2

]

uij

i, j ∈ Z+ (the set of nonnegative integers),

y (^) ij = C

[

x hij x vij

]

• Duij

Here x (^) ijh ∈ R n^1 and x vij ∈ R n^2 are the hori- zontal and vertical local state vectors, respec- tively, u (^) ij ∈ R m^ is the input vector, yij ∈ R p is the output vector and A 1 , A 2 , A 3 , A 4 , B 1 , B 2 , C, D are real matrices. The model was introduced by R.P. Roesser in “A discrete state-space model for linear image process- ing,” IEEE Trans. Autom. Contr., AC-20, No. 1, 1975, pp. 1-10.

2-D shuffle algorithm an extension of the Luenberger shuffle algorithm for 1-D case. The 2-D shuffle algorithm can be used for checking the regularity condition

det [Ez 1 z 2 − A 0 − A 1 z 1 − A 2 z 2 ] 6 = 0

for some (z 1 , z 2 ) ∈ C×C of the singular gen- eral model ( See singular 2-D general model).

The algorithm is based on the row compres- sion of suitable matrices.

2-D Z-transform F (z 1 , z 2 ) of a dis- crete 2-D function f (^) ij satisfying the condi- tion f (^) ij = 0 for i < 0 or/and j < 0 is defined by

F (z 1 , z 2 ) =

i= 0

∑^ ∞

j = 0

fij z− 1 iz− 2 j

An 2-D discrete fij has the 2-D Z-transform if the sum

∑^ ∞

i= 0

∑^ ∞

j = 0

fij z− 1 iz− 2 j

exists.

2DEGFET See high electron mobility transistor(HEMT).

2LG See double phase ground fault.

3-dB bandwidth for a causal low-pass or bandpass filter with a frequency function H (j ω) the frequency at which | H (j ω) |dB is less than 3 dB down from the peak value | H (ωP ) |.

3-level laser a laser in which the most important transitions involve only three en- ergy states; usually refers to a laser in which the lower level of the laser transition is sepa- rated from the ground state by much less than the thermal energy kT. Contrast with 4-level laser.

3-level system a quantum mechanical system whose interaction with one or more electromagnetic fields can be described by considering primarily three energy levels. For example, the cascade, vee, and lambda systems are 3-level systems.

4-level laser a laser in which the most important transitions involve only four en- ergy states; usually refers to a laser in which the lower level of the laser transition is sep- arated from the ground state by much more

than the thermal energy kT. Contrast with 3-level laser.

45 Mbs DPCM for NTSC color video a codec wherein a subjectively pleasing pic- ture is required at the receiver. This does not require transparent coding quality typical of TV signals. The output bit-rate for video matches the DS3 44.736 Megabits per second rate. The coding is done by PCM coding the NTSC composite video signal at three times the color subcarrier frequency using 8 bit per pixel. Prediction of current pixel is obtained by averaging the pixel three after current and 681 pixels before next to maintain the sub- carrier phase. A leak factor is chosen before computing prediction error to main the quali-

ty of the image. For example a leak factor of 31 32 the prediction decay is maintained at the center of the dynamic range.

X− L = 128 +

X−^ − 128

Finally, a clipper at the coder and decoder is employed to prevent quantization errors.

90% withstand voltage a measure of the practical lightning or switching-surge im- pulse withstand capability of a piece of power equipment. This voltage withstand level is two standard deviations above the BIL of the equipment.

dump. This is generally done to prevent in- jury to some personnel or damage to acceler- ator components.

ABR See available bit rate.

absolute address an address within an instruction that directly indicates a location in the program’s address space. Compare with relative addressing.

absolute addressing an addressing mode where the address of the instruction operand in memory is a part of the instruction so that no calculation of an effective address by the CPU is necessary. For example, in the Motorola M68000 ar- chitecture instruction ADD 5000,D1, a 16-bit word operand, stored in memory at the word address 5000, is added to the lower word in register D1. The address “5000” is an exam- ple of using the absolute addressing mode. See also addressing mode.

absolute encoder an optical device mounted to the shaft of a motor consisting of a disc with a pattern and light sources and detectors. The combination of light detectors receiving light depends on the position of the rotor and the pattern employed (typically the Gray code). Thus, absolute position infor- mation is obtained. The higher the resolution required, the larger the number of detectors needed. See also encoder.

absolute moment The pth order absolute moment μp of a random variable X is the expectation of the absolute value of X raised to the pth power:

μ (^) p = E[| X |]p^.

See also central moment, central absolute moment. See also expectation.

absolute pressure units to measure gas pressure in a vacuum chamber with zero be- ing a perfect vacuum. Normally referred to as psia (pounds per square inch absolute).

absolute sensitivity denoted S (y, x), is simply the partial derivative of y with respect to x, i.e., S (y, x) = ∂y/∂x, and is used to establish the relationships between absolute changes. See sensitivity, sensitivity measure, relative sensitivity, semi-relative sensitivity.

absolute stability occurs when the net- work function H (s) has only left half-plane poles.

absorber generic term used to describe material used to absorb electromagnetic en- ergy. Generally made of polyurethane foam and impregnated with carbon (and fire- retardant salts), it is most frequently used to line the walls, floors and ceilings of anechoic chambers to reduce or eliminate reflections from these surfaces.

absorbing boundary condition (ABC) a fictitious boundary introduced in differential equation methods to truncate the computa- tional space at a finite distance without, in principle, creating any reflections.

absorption (1) process that dissipates en- ergy and causes a decrease in the amplitude and intensity of a propagating wave between an input and output reference plane. (2) reduction in the number of photons of a specific wavelength or energy incident upon a material. Energy transferred to the material may result in a change in the electronic struc- ture, or in the relative movement of atoms in the material (vibration or rotation). (3) process by which atoms or molecules stick to a surface. If a bond is formed, it is termed chemisorption, while the normal case is physisorption. The absorption process pro- ceeds due to, and is supported by, the fact that this is a lower energy state.

absorption coefficient (1) in a passive de- vice, the negative ratio of the power absorbed (p absorbed = p in −p out ) ratioed to the power in (p in = p incident − p reflected ) per unit length (l), usually expressed in units of 1/wavelength or 1/meter.

(2) factor describing the fractional atten- uation of light with distance traversed in a medium, generally expressed as an exponen- tial factor, such as k in the function e−kx^ , with units of (length)-1. Also called attenu- ation coefficient.

absorption cross section energy ab- sorbed by the scattering medium, normal- ized to the wavenumber. It has dimensions of area.

absorption edge the optical wavelength or photon energy corresponding to the sep- aration of valence and conduction bands in solids; at shorter wavelengths, or higher pho- ton energies than the absorption edge, the ab- sorption increases strongly.

absorption grating (1) a diffraction grating where alternate grating periods are opaque. (2) an optical grating characterized by spatially periodic variation in the absorption of light. Absorption gratings are generally less efficient than phase gratings.

absorption optical fiber the amount of optical power in an optical fiber captured by defect and impurity centers in the energy bandgap of the fiber material and lost in the form of longwave infrared radiation.

AC See alternating current.

AC bridge one of a wide group of bridge circuits used for measurements of re- sistances, inductances, and capacitances, and to provide AC signal in the bridge transducers including resistors, inductors, and capacitors. The Wheatstone bridge can be used with a sinusoidal power supply, and with an AC detector (headphones, oscilloscope), one can use essentially the same procedure for mea- surement of resistors as in DC applications. Only a small number of other AC bridges are used in modern electric and electronic equip- ment. A strong selection factor was the fact that in a standard capacitor the electrical pa-

rameter are closest to the parameters of an ideal capacitor. Hence, not only a capaci- tance is measured in terms of capacitance (in resistive ratio arms bridges), but the induc- tance as well is measured in terms of capac- itance (Hay and Owen bridges). The AC bridges with ratio arms that are tightly coupled inductances allow measure- ment of a very small difference between cur- rents in these inductances, and this fact is used in very sensitive capacitance transduc- ers.

AC circuit electrical network in which the voltage polarity and directions of current flow change continuously, and often periodically. Thus, such networks contain alternating cur- rents as opposed to direct currents, thereby giving rise to the term.

AC coupling a method of connecting two circuits that allows displacement current to flow while preventing conductive currents. Reactive impedance devices (e.g., capacitors and inductive transformers) are used to pro- vide continuity of alternating current flow between two circuits while simultaneously blocking the flow of direct current.

AC motor an electromechanical sys- tem that converts alternating current electri- cal power into mechanical power.

AC plasma display a display that em- ploys an internal capacitive dielectric layer to limit the gas discharge current.

AC steady-state power the average power delivered by a sinusoidal source to a network, expressed as

P =| V | · | I | cos(θ)

where

2 · | V | and

2 · | I | are the peak values, respectively, of the AC steady-state voltage and current at the terminals. θ rep- resents the phase angle by which the voltage leads the current.

access control a means of allowing ac- cess to an object based on the type of ac- cess sought, the accessor’s privileges, and the owner’s policy.

access control list a list of items associ- ated with a file or other object; the list con- tains the identities of users that are permitted access to the associated file. There is infor- mation (usually in the form of a set of bits) about the types of access (such as read, write, or delete) permitted to the user.

access control matrix a tabular repre- sentation of the modes of access permitted from active entities (programs or processes) to passive entities (objects, files, or devices). A typical format associates a row with an ac- tive entity or subject and a column with an object; the modes of access permitted from that active entity to the associated passive en- tity are listed in the table entry.

access line a communication line that connects a user’s terminal equipment to a switching node.

access mechanism a circuit board or an integrated chip that allows a given part of a computer system to access another part. This is typically performed by using a specific ac- cess protocol.

access protocol a set of rules that estab- lishes communication among different parts. These can involve both hardware and soft- ware specifications.

access right permission to perform an operation on an object, usually specified as the type of operation that is permitted, such as read, write, or delete. Access rights can be included in access control lists, capability lists, or in an overall access control matrix.

access time the total time needed to re- trieve data from memory. For a disk drive this is the sum of the time to position the read/write head over the desired track and the

time until the desired data rotates under the head. (LW)

accidental rate the rate of false coinci- dences in the electronic counter experiment produced by products of the reactions of more than one beam particle within the time reso- lution of the apparatus.

accumulation (1) an increase in the ma- jority carrier concentration of a region of semiconductor due to an externally applied electric field.

accumulator (1) a register in the CPU (processor) that stores one of the operands prior to the execution of an operation, and into which the result of the operation is stored. An accumulator serves as an implicit source and destination of many of the pro- cessor instructions. For example, register A of the Intel 8085 is an accumulator. See also CPU. (2) the storage ring in which successive pulses of particles are collected to create a particle beam of reasonable intensity for col- liding beams.

achievable rate region for a multiple terminal communications system, a set of rate-vectors for which there exist codes such that the probability of making a decoding er- ror can be made arbitrarily small. See also capacity region, multiple access channel.

achromatic the quality of a transport line or optical system where particle momentum has no effect on its trajectory through the sys- tem. In an achromatic device or system, the output beam displacement or divergence (or both) is independent of the input beam’s mo- mentum. If a system of lenses is achromatic, all particles of the same momentum will have equal path lengths through the system.

ACI See adjacent channel interference.

acknowledge (1) a signal which indicates that some operation, such as a data transfer, has successfully been completed. (2) to detect the successful completion of an operation and produce a signal indicating the success.

acoustic attenuation the degree of am- plitude suppression suffered by the acous- tic wave traveling along the acousto-optic medium.

acoustic laser a laser (or maser) in which the amplified field consists of soundwaves or phonons rather than electromagnetic waves; phonon laser or phaser.

acoustic memory a form of circulating memory in which information is encoded in acoustic waves, typically propagated through a trough of mercury. Now obsolete.

acoustic velocity the velocity of the acoustic signal traveling along the acousto- optic medium.

acoustic wave a propagating periodic pressure wave with amplitude representing either longitudinal or shear particle displace- ment within the wave medium; shear waves are prohibited in gaseous and liquid media.

acousto-optic cell a device consisting of a photo-elastic medium in which a propa- gating acoustic wave causes refractive-index changes, proportional to acoustic wave am- plitude, that act as a phase grating for diffrac- tion of light. See also Bragg cell.

acousto-optic channelized radiometer See acousto-optic instantaneous spectrum analyzer in Bragg mode.

acousto-optic correlator an optical sys- tem that consists of at least one acousto- optic cell, imaging optics between cells and fixed masks, and photodetectors whose out- puts correspond to the correlation function of the acoustic wave signal within one cell with

another signal in a second cell, or with fixed signals on a mask.

acousto-optic deflector device device where acousto-optic interaction deflects the incident beam linearly as a function of the input frequency of the RF signal driving the device.

acousto-optic device descriptor of acousto-optic cells of any design; generally describes a cell plus its transducer struc- ture(s), and may encompass either bulk, guided-wave, or fiber-optic devices.

acousto-optic effect the interaction of light with sound waves and in particular the modification of the properties of a light wave by its interactions with an electrically con- trollable sound wave. See also Brillouin scattering.

acousto-optic frequency excisor similar to an acousto-optic spectrum analyzer where the RF temporal spectrum is spatially and se- lectively blocked to filter the RF signal feed- ing the Bragg cell.

acousto-optic instantaneous spectrum an- alyzer in Bragg mode device in which the temporal spectrum of a radio frequency sig- nal is instantaneously and spatially resolved in the optical domain using a Fourier trans- form lens and a RF signal-fed Bragg cell.

acousto-optic modulator a device that modifies the amplitude or phase of a light wave by means of the acousto-optic effect.

acousto-optic processor an optical sys- tem that incorporates acousto-optic cells con- figured to perform any of a number of math- ematical functions such as Fourier trans- form, ambiguity transforms, and other time- frequency transforms.

acousto-optic scanner a device that uses an acoustic wave in a photoelastic medium

of a neuron to a smaller set of values. This set is usually [ 0 , 1 ]. Typical functions are the sigmoid function or singularity functions like the step or ramp.

active contour a deformable template matching method that, by minimizing the energy function associated with a specific model (i.e., a specific characterization of the shape of an object), deforms the model in conformation to salient image features.

active device a device that can convert energy from a DC bias source to a signal at an RF frequency. Active devices are required in oscillators and amplifiers.

active filter (1) a filter that has an en- ergy gain greater than one, that is, a filter that outputs more energy than it absorbs.

(2) a form of power electronic converter designed to effectively cancel harmonic cur- rents by injecting currents that are equal and opposite to, or 180◦^ out of phase with, the tar- get harmonics. Active filters allow the out- put current to be controlled and provide sta- ble operation against AC source impedance variations without interfering with the system impedance.

The main type of active filter is the series type in which a voltage is added in series with an existing bus voltage. The other type is the parallel type in which a current is injected into the bus and cancels the line current har- monics.

active impedance the impedance at the input of a single antenna element of an ar- ray with all the other elements of the array excited.

active layer See active region.

active learning a form of machine learn- ing where the learning system is able to in- teract with its environment so as to affect the generation of training data.

active load a transistor connected so as to replace a function that would conventionally be performed by a passive component such as a resistor, capacitor, or inductor.

active load-pull measurement a mea- surement method where transfer characteris- tics of a device can be measured by electri- cally changing the load impedance seen from the device. In an active load-pull measure- ment, the load impedance is defined by using an output signal from the device and an in- jected signal from the output of the device.

active logic a digital logic that operates all of the time in the active, dissipative region of the electronic amplifiers from which it is constructed. The output of such a gate is determined primarily by the gate and not by the load.

active magnetic bearing a magnetic bearing that requires input energy for stable support during operation. Generally imple- mented with one or more electromagnets and controllers.

active mixer a mixer that uses three termi- nal devices such as FET rather than diodes as nonlinear element. One advantage of active mixers is that they can provide conversion gain.

active network an electrical network that contains some solid state devices such as bipolar junction transistors (BJTs) or metal- oxide-silicon field effect transistors (FETs) operating in their active region of the volt- age vs. current characteristic. To ensure that these devices are operating in the active re- gion, they must be supplied with proper DC biasing.

active neuron a neuron with a non-zero output. Most neurons have an activation threshold. The output of such a neuron has zero output until this threshold is reached.

active power See real power.

active power line conditioner a device which senses disturbances on a power line and injects compensating voltages or currents to restore the line’s proper waveform.

active RC filter an electronic circuit made up of resistors, capacitors, and opera- tional amplifiers that provide well-controlled linear frequency-dependent functions, e.g., low-, high-, and bandpass filters.

active redundancy a circuit redundancy technique that assures fault-tolerance by de- tecting the existence of faults and performing some action to remove the faulty hardware, e.g., by standby sparing.

active region semiconductor material doped such that electrons and/or holes are free to move when the material is biased. In the final fabricated device, the active regions are usually confined to very small portions of the wafer material.

active-high (1) a logic signal having its asserted state as the logic ONE state.

(2) a logic signal having the logic ONE state as the higher voltage of the two states.

active-low (1) a logic signal having its asserted state as the logic ZERO state.

(2) a logic signal having its logic ONE state as the lower voltage of the two states; inverted logic.

actuator (1) a transducer that converts electrical, hydraulic, or pneumatic energy to effective motion. For example in robots, ac- tuators set the manipulator in motion through actuation of the joints. Industrial robots are equipped with motors that are typically electric, hydraulic, or pneumatic. See also industrial robot.

(2) in computers, a device, usually me- chanical in nature, that is controlled by a computer, e.g., a printer paper mechanism or a disk drive head positioning mechanism.

ACTV See advanced compatible tele- vision.

acuity sharpness. The ability of the eye to discern between two small objects closely spaced, as on a display.

adaptability the capability of a system to change to suit the prevailing conditions, espe- cially by automatic adjustment of parameters through some initialization procedure or by training.

adaptation layer control layer of a mul- tilayer controller, situated above the direct control layer and — usually — also above the optimizing control layer, required to intro- duce changes into the decision mechanisms of the layer (or layers) below this adaptation layer; for example adaptation layer of the in- dustrial controller may be responsible for ad- justing the model used by the optimizing con- trol and the decision rules used by the direct (regulation) control mechanisms.

adapter a typical term from personal computers. A circuit board containing the interface toward an additional peripheral de- vice. For example, a graphic adapter (inter- face boards like EGA, VGA, CGA), a game controller, a SCSI controller, a PCMCI inter- face, etc.

adaptive algorithm (1) a method for ad- justing the parameters of a filter to satisfy an objective (e.g., minimize a cost function). (2) an algorithm whose properties are ad- justed continuously during execution with the objective of optimizing some criterion.

adaptive antenna antenna, or array of antennas, whose performance characteristics can be adapted by some means; e.g., the pattern of an array can be changed when the phasing of each of the array elements is changed.

adaptive array an array that adapts itself to maximize the reception of a desired sig-

remaining layers are elementary logic gates, usually AND and OR gates. Each linear threshold unit is trained to fit input data in those regions of the input space where it is active (i.e., where it contributes to the overall network function).

adaptive manipulator controller a con- troller that uses an adaptation process which, based on observation of the manipulator po- sition and velocity, readjusts the parameters in the nonlinear model until the errors dis- appear. An adaptive manipulator controller is depicted in the figure below. Such a sys- tem would learn its own dynamic properties. The adaptive manipulator control scheme

Adaptive manipulator control scheme.

presented in the figure belongs to the joint space control schemes. See also joint space control.

adaptive predictor a digital filter whose coefficients can be varied, according to some error minimization algorithm, such that it can predict the value of a signal say N sampling time intervals into the future. The adaptive predictor is useful in many interference can- cellation applications.

adaptive resonance theory (ART) network A clustering network developed to allow the learning of new information without destroy- ing what has already been learnt. Each clus- ter is represented by a prototype and learning is achieved by comparing a new input pat- tern with each prototype. If a prototype is found that is acceptably close to that input,

the new pattern is added to that prototype’s cluster and the prototype is adjusted so as to move closer to the new input. If no pro- totype is acceptable, the pattern becomes a new prototype around which a new cluster may develop.

adaptive vector quantization term that refers to methods for vector quantization that are designed to adaptively track changes in the input signal.

ADC See analog-to-digital converter.

ADCPM See adaptive differential pulse code modulation.

add instruction a machine instruction that causes two numeric operands to be added together. The operands may be from machine registers, memory, or from the instruction it- self, and the result may be placed in a ma- chine register or in memory.

adder a logic circuit used for adding bi- nary numbers.

additive acousto-optic processing acousto-optic signal processing where the summation of acousto-optic modulated light waves is used to implement the signal pro- cessing operation.

additive polarity polarity designation of a transformer in which terminals of the same polarity on the low- and high-voltage coils are physically adjacent to each other on the transformer casing. With additive polarity, a short between two adjacent terminals results in the sum of the two coil voltages appearing between the remaining terminals. Additive polarity is generally used for transformers up to 500kVA and 34.5kV. Larger units use sub- tractive polarity. See the diagram below. See also subtractive polarity.

additive white Gaussian noise (AWGN) the simplest form of channel degradation in a communication system in which the source

Transformer with additive polarity.

of errors in the channel can be modeled as the addition of random noise with a Gaus- sian distribution and a constant (white) power spectrum. See also thermal noise.

address a unique identifier for the place where information is stored (as opposed to the contents actually stored there). Most stor- age devices may be regarded by the user as a linear array, such as bytes or words in RAM or sectors on a disk. The address is then just an ordinal number of the physical or logical position. In some disks, the address may be compound, consisting of the cylinder or track and the sector within that cylinder. In more complex systems, the address may be a “name” that is more relevant to the user but must be translated by the underlying software or hardware.

address aliasing See cache aliasing.

address bus the set of wires or tracks on a backplane, printed circuit board, or in- tegrated circuit to carry binary address sig- nals between different parts of a computer. The number of bits of address bus (the width of the bus) determines the maximum size of memory that can be addressed. Modern mi- crochips have 32 address lines, thus 4 giga- bytes of main memory can be accessed.

address decoder logic that decodes an address.

1. A partial decoder responds to a small range of addresses and is used when recog- nizing particular device addresses on an I/O address bus, or when recognizing that ad- dresses belong to a particular memory mod- ule. 2. A full decoder takes N bits and asserts one of 2N^ outputs, and is used within mem- ories (often within RAM chips themselves).

address error an exception (error inter- rupt) caused by a program’s attempt to access unaligned words or long words on a proces- sor that does not accommodate such requests. The address error is detected within the CPU. This contrasts with problems that arise in ac- cessing the memory itself, where a logic cir- cuit external to the CPU itself must detect and signal the error to cause the CPU to process the exception. Such external problems are called bus errors.

address field the portion of a program instruction word that holds an address.

address generation interlock (AGI) a mechanism to stall the pipeline for one cycle when an address used in one machine cycle is being calculated or loaded in the previous cycle. Address generation interlocks cause the CPU to be delayed for a cycle. (AGIs on the Pentium are even more important to remove, since two execution time slots are lost).

address locking a mechanism to protect a specific memory address so that it can be accessed exclusively by a single processor.

address map a table that associates a base address in main memory with an object (or page) number.

address mapping the translation of vir- tual address into real (i.e., physical) ad- dresses for memory access. See also virtual memory.

address register a register used primarily to hold the address of a location in memory. The location can contain an operand or an executable instruction.

address size prefix a part of a machine instruction that provides information as to the

lation trapping. Adiabatic passage is often used for selective transfer of population be- tween two long-lived states of a multistate system, especially in cases where the two- step process of absorption followed by spon- taneous decay (optical pumping) would tend to populate many other states.

adjacency graph a graph in which each node represents an object, component, or fea- ture in an image. An edge between two nodes indicates two components that are touching or connected in the image.

adjacent channel interference (ACI) the interference caused by an adjacent frequency band, e.g., in a system with frequency divi- sion duplex (FDD). Classified as either in- band or out-of-band adjacent channel inter- ference (ACI). The in-band ACI occurs when the center frequency of interfering signal falls within the band of the desired signal. The out-of-band ACI occurs when the center fre- quency of interfering signal falls outside the bandwidth of the desired signal.

adjacent channel leakage power See adjacent channel power.

adjacent channel power (ACP) a power of distortion components generated in adja- cent channel, which is caused by a nonlinear- ity of high-power amplifier amplifying a dig- itally modulated signal such as QPSK, QAM, etc. Adjacent channel power is defined as a ratio of signal power in channel and leakage power in adjacent channel.

adjacent channel reuse ratio (ACRR) the reuse ratio between radio communication cells using adjacent radio channels. See also reuse ratio.

adjacent channels radio channels occu- pying radio frequency allocations n and n±1.

adjoint network a network with an iden- tical structure to the original one, but with possibly different elements. As an exam-

ple, for a network described by the nodal ad- mittance matrix, its adjoint network is repre- sented by the transposed admittance matrix of the original network. The adjoint network is a basic tool in the computer-aided sensi- tivity analysis of electronic and microwave circuits.

adjustable-speed drive See variable speed DC drive, variable speed AC drive.

admissible matrix a matrix M−^ that can be obtained by fixing the free parameters of the matrix M at some particular values. M− is said to be admissible with respect to M.

admittance the reciprocal of the impedance of an electric circuit.

admittance inverter an idealized de- vice or set of matrix parameters that func- tions electrically like a quarter-wave lossless transmission line of characteristic impedance J at each frequency, thus transforming the load admittance (Y LOAD ) by +90 degrees and modifying the magnitude, resulting in an in- put admittance (Y (^) in).

Yin =

J 2

Y load

admittance matrix the inverse of the impedance matrix in the method of moments.

ADP See ammonium dihydrogen phosphate.

ADPCM See adaptive differential pulse code modulation.

ADSL See asymmetric digital subscriber line.

adsorbent the material of an adsorber, for example, silica gel, alumina, and char- coal. Adsorbent materials are characterized by high surface to volume ratio.

adsorber (1) condensation of a gas on the solid material.

(2) material that attracts and holds (by Van der Waal forces) molecular layers of dense gases (i.e., very near condensation temper- atures) on porous high surface/volume ratio materials.

ADTV See advanced digital television.

advanced compatible television (ACTV) an extended definition television system that can operate with existing bandwidths on ex- isting receivers and is compatible with the NTSC broadcasting system. The ACTV sys- tem was proposed by the Advanced Televi- sion Research Consortium and was the first high definition television (HDTV) system. HDTV system was tested by the FCC July 17, 1992. The additional picture information needed to increase the picture width and to increase the resolution to the HDTV format is transmitted in an augmented channel as an alternative to simulcast transmission. See Advanced Television Research Consortium.

advanced digital television (ADTV) a high definition television (HDTV) digital transmission television system was proposed to the Federal Communications Commission by the Advanced Television Research Con- sortium. The ADTV system introduced a layered system to separately describe the dig- ital transmission system, the video compres- sion system, and the data packet transport system. The video compression method uses a MPEG++ standard that provides for com- patibility with multimedia computing. See Advanced Television Research Consortium.

advanced mobile phone system (AMPS) a standard for a cellular radio communi- cations network originally developed in the 1970s by AT&T and later adopted as an in- dustry standard by the U.S.-based Telecom- munications Industries Association (TIA). It is the first cellular standard widely deployed in North America. It is also referred to as the analog cellular system. Frequency modula- tion with 30 kHz channels is used.

Advanced Television Research Consor- tium an organization consisting of David Sarnoff Research Center, Thompson Con- sumer Electronics, North American Philips Corporation, NBC, and Compression Labo- ratories.

aeolian vibration a high-frequency me- chanical vibration of electric power lines caused by wind.

aerial cable any fully-insulated electric power cable which is carried overhead upon poles, as opposed to the use of the more usual overhead bare conductors.

aerodynamic head See disk head.

AFC See automatic frequency control.

affine transform a geometric image transformation including one or more transla- tions, rotations, scales, and shears that is rep- resented by a 4 × 4 matrix allowing multiple geometric transformations in one transform step. Affine transformations are purely lin- ear and do not include perspective or warping transformations.

AFM See atomic force microscope.

AFT See automatic fine tuning.

AFV See audio follow-video switcher.

AGC See automatic gain control or automatic generation control.

agent a computational entity that acts on behalf of other entities in an autonomous fashion.

agent-based system an application whose component are agents. See also agent.

aggregation an operation performed on system variables whose purpose is to collect them in a way enabling order and/or uncer- tainty reduction. For linear systems both