Glossary of Terms
| Term | Definition |
|---|---|
| D Channel | Full duplex 16 kbps (basic rate) or 64 kbps (primary rate) ISDN channel. |
| D-AMPS | Digital Advanced Mobile Phone System. An American standard for digital mobile telephony used primarily in North America, Latin America, Australia and parts of Russia and Asia, now commonly referred to as TDMA. |
| Dark current | The thermally induced current that exists in a photodiode in the absence of incident optical power. |
| Data Circuit-terminating Equipment | Equipment that resides at the customer end of a transmission link and provides all necessary termination function for that link. May be owned by the customer or by the service provider. |
| Data rate | The number of bits of information in a transmission system, expressed in bits per second (bps), and which may or may not be equal to the signal or baud rate. |
| Data rate | The speed, measured in bits per second, that a particular network (or other application) transmits data. |
| Data Terminal Equipment (DTE) | The part of a data station that serves as a data source, destination, or both, and that provides for the data communications control function according to protocol. DTE includes computers, protocol translators, and multiplexers. |
| dB | Abbreviation for decibel.The logarithmic ratio of two powers, voltages or currents. |
| dBm | An abbreviation for decibels referred to one milliwatt. A term used to denote power level; i.e. 0 dBm is equal to 1 milliwatt. |
| DBS | direct broadcast satellite |
| dbtt | Decibel referenced to a microwatt. |
| DC | Direct Current - A flow of charge carriers within a medium in a single direction. |
| DC Bias | Direct current (DC) applied to the winding of a core in addition to any time-varying current. Inductance with DC bias is a common specification for powder cores. The inductance will 'roll off' gradually and predictably with increasing DC bias. |
| DC Filter | A filter circuit that removes the AC ripple from a mostly DC current. Usually this is done by using an inductor and capacitor together. |
| DC Stress | Annealing a magnetic material in the presence of a DC magnetic field to enhance magnetic properties. |
| DC-DC Converter | A circuit or device that converts a DC input voltage (usually unregulated) to a regulated DC output voltage. The output voltage may be lower, higher, or the same as the input voltage. Switching regulator DC-DC circuits most often require an inductor or transformer to achieve the regulated output voltage. Switching regulator circuits can achieve a higher level of power efficiency when compared to non-switching techniques. |
| DCE | Data Communications Equipment(EIA expansion) or Data Circuit-Terminating Equipment (CCITT expansion)- The devices and connections of a communications cicuit with the end device (data terminal equipment). A modem can be considered a DCE. |
| DCR | Direct Current Resistance - The resistance of the inductor winding measured with no alternating current. The DCR is most often minimized in the design of an inductor. The unit of measure is ohms and it is usually specified as a maximum rating. |
| DCS 1800 | A variant of GSM operating at or near 1.8 GHz. |
| DCS 1900 | A variant of GSM operating at or near 1.9 GHz used in the United States. |
| deci | A prefix which indicates a factor 10-1 (one tenth). Abbreviated as "d." |
| Decibel | One tenth of a Bel (B). The abbreviation for decibel is "dB." If N = P1/P2 is the ratio of two powers, then this ratio, N, expressed in decibels, is N = 10 log10(P1/P2). |
| Decoupling | Refers to a magnetic circuit where comparatively more of the flux generated by the MMF fringes around the magnetic material instead of entering it. |
| DECT | Digital European Cordless Telephone. |
| Dedicated Line | A transmission circuit installed between two sites of a private network and "open," or available, at all times. |
| deka | A prefix that indicates a factor 10, abbreviated as "da." |
| Delay Line | A transmission line or circuit that imposes a desired amount of propagation delay on an incident signal. Delay lines may also be specified in terms of the phase shift they produce as a result of the propagation delay. |
| Delay skew | The difference in propagation delay between the slowest and fastest pairs in a cable or system. |
| Delta | Arithmetic difference between two numbers, or the change in value of a parameter. |
| Demagnetization Curve | That portion of the hysteresis loop that lies between the residual induction point (BR) and the coercive force point (HC). |
| Demagnetized | A material condition where a ringing AC field has reduced the remnant induction to or near zero. A ringing AC field is a continually decreasing sinusoidal field. A pulsed DC field can be used to achieve gross demagnetization, but with much effort and with residual local magnetization. |
| Demodulation | The process of recovering intelligence from a signal, some parameter of which was modified to carry the intelligence (see modulation). |
| Density | See Power Density. |
| Depletion Layer | The insulating region in a rectifying semiconductor junction immediately surrounding and including the junction, caused by the space charge that occurs at the junction, which acts to deplete the concentration charge carriers in the region. |
| Derating | For a DC-DC converter, the specified reduction in output power required for operation at elevated temperatures. The most common operating temperature reange specified. Also see Convection Cooled. |
| Desensitization | The reduction in receiver sensitivity that is the result of the presence of large magnitude, off-channel signals. |
| Detector | (1) A circuit that produces a low frequency output signal, typically DC or video, whose amplitude is dependent upon the RF incident power level. The semiconductor element in a detector is typically a Schottky diode, FET or a tunnel diode. (2) An optoelectronic transducer used in fiber optics for converting optical power to electric current. In fiber optics, usually a photodiode. |
| DGPS | Differential GPS |
| Dial up | A type of communication that is established by a switched-circuit connection using the telephone network. |
| Diameter-mismatch loss | The loss of power at a joint that occurs when the transmitting half has a diameter greater than the diameter of the receiving half. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector. |
| Dichroic filter | An optical filter that transmits light selectively according to wavelength. |
| Dielectric | A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. Placing a dielectric between two metal plates, across which a voltage is applied, results in a slight separation of the positive and negative charges in the dielectric. This charge separation helps support the electric field between the plates and can store energy. This property is useful in capacitors, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines. |
| Dielectric Breakdown | The voltage required to cause an electrical failure or breakthrough of the insulation. Determined by a destructive test. See also Breakdown Voltage. |
| Dielectric Constant | (also K) The ratio of the capacitance between two electrodes with a solid, liquid, or gaseous dielectric, to the capacitance with air between the electrodes. Also called permittivity and specific inductive capacity.Generally low values are desirable for insulation. |
| Dielectric Loss | The time rate at which electric energy is converted into heat energy in a dielectric that is subjected to a varying electric field. |
| Dielectric Strength | The maximum allowable AC rms voltage (50 or 60 Hz) which may be applied between two test points, such as the coil and case or current carrying and non-current carrying points, without a leakage current in excess of 1 milliamp. |
| Dielectric Strength - Electric Strength - Hipot | The two most important, basic, and unique features that signal-isolation transformers provide are balance and physical separation, i.e. a dielectric barrier. The physical separation of the primary and secondary windings (or line-side and chip-side windings) allows sensitive low-voltage circuits to be safely electromagnetically connected to circuit nodes exposed to high voltage potentials without a direct conductive path. The voltage rating of a transformer is called out by its dielectric strength level in VACRMS or VDC. The transformer is guaranteed to isolate the primary and secondary windings from high-voltage transients below this rated level. The typical dielectric level for most telecom applications is 1500VACRMS for a one minute duration. At some voltage potential, a leakage current will begin to flow through the protective insulation. When the magnitude of this current exceeds a predefined level (typically 500µA), Insulation Breakdown or Dielectric Breakdown is said to have occurred. As per UL1950 (5.3.2): "Insulation breakdown is considered to have occured when the current which flows as a result of the application of the test voltage rapidly increses in an uncontrolled manner, i.e. the insulation does not restrict the flow of the current. Corona discharge or a single momentary flashover is not regarded as insulation breakdown." |
| Dielectric Withstand Voltage | DWV - The voltage level at which the dielectric breaks down, allowing conduction between isolated conductors or between a conductor and the core. Isolation, or hipot is the ability of a transformer to withstand a specific breakdown voltage between the primary and secondary windings. |
| Differential Mode | A current conduction mode in which currents, relative to two conductors, are flowing 180¡ out of phase, with equal magnitude within the conductors. |
| Differential Mode Current | The intended signal currents that are equal and oppositely directed on pairs of signal and return (ground) conductors. |
| Differential Mode Noise | Also known as normal-mode noise. It is the electrical interference that is not common to both lines, but is present between both lines. |
| Differential Mode Voltage | The voltage that drives equal and oppositely directed currents to achieve an intended circuit function. The source of differential mode current. |
| Diffraction grating | An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light. |
| Diffusion | The movement of electrical charge carriers or particles from regions of high concentration to regions of lower concentration. In semiconductor fabrication, the movement of impurity atoms during high temperature annealing. |
| Digital | Having or pertaining to the use of numbers expressed in digits to represent all of the variables of a system. Using, pertaining to, or consisting of that class of devices whose performance varies only in discrete steps. |
| Digital Signal 0 (DS-0) | North American Digital Hierarchy signaling standard for transmission at 64 kbps. (2) Digital Signal Level 0 is the worldwide standard transmission rate (64 kbps) for PCM digitized voice channels. 24 DSOs exist in each DSI (T1) signal. |
| Digital Signal 1 (DS-1) | North American Digital Hierarchy signaling standard for transmission sat 2.544 Mbps. Supports 24 simultaneous DS-O signals. Term often used interchangeably with T-1, although DS-1 signals may be exchanged over other transmission systems. |
| Diode | A two-terminal device which has nonlinear and asymmetrical (about zero) voltage versus current characteristics. |
| Diplexer | A circuit or system that allows the ability to transmit and receive two distinct signals simultaneously. |
| Diplexing | The simultaneous transmission or reception of two signals though a common component, such as an antenna. |
| Direct Current | A flow of charge carriers within a medium in a single direction. |
| Direct Current Resistance | DCR - The resistance of the inductor winding measured with no alternating current. The DCR is most often minimized in the design of an inductor. The unit of measure is ohms and it is usually specified as a maximum rating. |
| Direction of Lay | The lateral direction in which the strands or elements of a cable run over the top of the cable as they recede from the observer. Expressed as right-hand or left-hand lay. |
| Directional Coupler | A four port device that transmits the majority of signal power incident on its input port to the output port and the remainder of the signal power to a third, coupled port. Signals incident on the output port are coupled to the fourth, coupled port, which may be terminated with a resistor equal in value to the coupler's characteristic impedance. The ratio of the coupled power to the input power is the coupling factor. |
| Disable | The act of de-asserting the enable signal to turn off the device. In the case of an EN low device, the EN signal must fall below the typical threshold voltage of 1.5V. |
| Disaccommodation (DF) | The proportional decrease of permeability after a disturbance of a magnetic material, measured at a constant temperature, over a given time interval. The resultant permeability after magnetic conditioning divided by the permeability of the first measurement times log10 of the ratio of time interval. |
| Discontinuity | A broken connection, or the loss of a specific connection characteristic. Also, the temporary interruption or variation in current or voltage. |
| Discrete | Complete in and of itself. In electronics, a discrete component consists of a single circuit element in a package, for example a diode or transistor. In practice, some components considered discrete may actually consist of a few simple circuit elements in a single package. |
| Discrete Air Gap | Mechanical air gap created by a small number of breaks in the magnetic path. In a standard C-core this number is generally two, a standard E-core is generally three, etc. |
| Discriminator | A tuned circuit that produces an output voltage, the amplitude and polarity of which are determined by the frequency of the input signal. A discriminator is used as the demodulator in an FM receiver. |
| D-ISDN | broadband integrated services digital network |
| Dispersion | A general term for those phenomena that cause a broadening or spreading of light as it propagates through an optical fiber. The three types are modal, material, and waveguide. |
| Dissipation | The conversion of electrical energy to heat energy in a component. |
| Dissipation Factor | The ratio between the permittivity and the conductivity of a dielectric. |
| Distortion | Any deviation from the mathematical ideal of a real-world periodic waveform, which is specified as a percent of the desired signal. Distortion can be expressed mathematically in terms of the harmonics of the fundamental frequency. This parameter is of considerable importance in instrumentation transformers. |
| Distortion-limited operation | Generally synonymous with bandwidth-limited operation. |
| Distributed Air Gap | A major feature of iron powder cores. It is the cumulative effect of many small gaps distributed evenly throughout the core. In a typical MPP core, the number of separate air gaps results from the use of powder to construct the core and numbers in the millions. The result is minimal fringing flux density compared to a core with one or two discrete air gaps in the magnetic path. |
| Distributed Capacitance | (1) In the construction of an inductor, each turn of wire or conductor acts as a capacitor plate. The combined effects of each turn can be presented as a single capacitance known as the distributed capacitance. The capacitance is in parallel with the inductor. This parallel combination will resonate at some frequency, which is called the self-resonant frequency (SRF). Lower distributed capacitance for a given inductance will result in a higher SRF and vice versa. (2) Capacitance that is not concentrated within a lumped capacitor, but spread over a circuit or group of components. |
| Distributed Inductance | Inductance that is not concentrated within a lumped inductor, but spread over a circuit or group of components. |
| Distributed Power | System level architecture in which converters operating from a central power bus provide localized power (and various voltage levels) to individual subassemblies/components. The type of power distribution system used is highly dependent upon the needs of a particular application. |
| DLC | digital loop carrier |
| DLEC | digital local carrier |
| DMA | Direct Memory Access, it bypasses the CPU-peripheral bottleneck and permits the transfer of data between a peripheral and the microcomputer's random access memory without the active intervention of the CPU. |
| DMT | Discrete Multitone. In DMT, a large number of low-rate carrier frequencies are QAM-modulated at a low rate to transmit a single high-rate data stream. DMT is used for ADSL and proposed for VDSL. |
| DOCSIS | Data Over Cable System Interface Specification |
| DoD | The United States Department of Defense. (which manages and controls the GPS) |
| Donor | A material that is intentionally added to a pure semiconductor material in order to increase the population of free electrons in that semiconductor, resulting in a net negative charge. A semiconductor that has had donor material added to it is called "n-type." |
| DOP | Dilution Of Precision |
| Dopant | An impurity added to a pure substance to alter the behavior or properties of the pure substance. Dopants in semiconductors are either charge carrier donors or acceptors, and make the semiconductor either n-type (surplus electrons), or p-type (shortage of electrons). |
| Doping | The intentional addition of a foreign substance to a pure substance in order to alter the behavior or properties of the pure substance. |
| Doppler Effect | The apparent shift in frequency of an incident wave that is the result of relative velocity between the emitter of the wave and the receiver of the wave. The Doppler shift frequency (fd) is given by: fd = 2 V (f0 / c) cosF, where: f0 is transmitter frequency in Hz, c is velocity of light (3 x 108 meters per second), V is the magnitude of the relative velocity (meters per second), æ is the angle between the incident wave and target's path. Note: cos æ is 1 for motion directly toward or away from the receiver. Velocity (V) is a vector that determines the sign of doppler shift frequency. |
| Doppler Radar | A radar system that uses the Doppler effect to measure presence and velocity of a target. The commercial Doppler systems, such as police radars and intrusion alarms, usually operate with a "zero IF" because the transmitter source (Gunn oscillator) is also used as the local oscillator for the mixer. Using this technique, the frequency of the IF signal is the Doppler shift frequency. For example, if the transmitter frequency is 10.525 GHz, a vehicle traveling at 50 mph will cause a Doppler shift of 1568 Hz. |
| Doppler Shift | The apparent shift in frequency of an incident wave that is the result of relative velocity between the emitter of the wave and the receiver of the wave. The Doppler shift frequency (fd) is given by: fd = 2 V (f0 / c) cosF, where: f0 is transmitter frequency in Hz, c is velocity of light (3 x 108 meters per second), V is the magnitude of the relative velocity (meters per second), æ is the angle between the incident wave and target's path. Note: cos æ is 1 for motion directly toward or away from the receiver. Velocity (V) is a vector that determines the sign of doppler shift frequency. |
| Double Balanced Mixer | A frequency translation circuit, which consists of four components with nonlinear impedance, typically Schottky diodes or FET's, connected in a ring quad configuration, with balun transformers at the RF and LO inputs to connect unbalanced transmission lines to the balanced quad. The IF output is via an unbalanced transmission line. The term balanced mixer is used to imply that neither of the input terms will appear at the mixer output. In practice, suppression of these input components is never perfect in an analog mixer circuit. Both types of mixer produce signals at odd harmonics of the carrier frequency, particularly the diode ring mixer. In most cases, these can be easily filtered out. |
| Downconverter (Mixer) | A mixer whose desired output signal called the IF signal is the difference of the incident RF and LO signals. |
| DQPSK | Differential quadrature phase shift key modulation. |
| DR | Dead Reckoning |
| Drain | The terminal at one end of the channel of a field effect transistor (FET) from which electron or hole current leaves the channel. This terminal corresponds to the collector in a bipolar transistor. |
| Drain Wire | In a cable, an uninsulated conductor laid over the component, or components, in a foil-shield cable. Used as a ground connection. |
| Drift | Change in the output voltage of a converter over a specified period of time. All other operating parameters (load, line, etc.) are assumed to be held constant. Often specified as starting after a warm up period. |
| Driver | A circuit that supplies an input to another circuit, and (usually) provides a level boost, impedance matching, or isolation. |
| Drop | Refers to the horizontal cabling for one work area, as in "The job has 100 drops." |
| Drop Cable | A cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from the network node to a transceiver (a transmit/receiver) attached to the trunk cable. |
| Drop-out Voltage | The voltage at which all contacts return to their “normal”, unoperated positions. (Applicable only to non-latching relays.) |
| DSL | Digital Subscriber Line- Another name for an ISDN BRI channel. Operated at the Basic Rate Interface (with two 64 kbps circuit switched channels and one 16 kbps packet switched channel), the DSL can carry both voice and data signal at the same time, in both directions, as well as the signaling data used for call information and customer data. |
| DSLAM | digital subscriber line access multiplexer |
| DSP | Digital Signal Processor- The processing of signal transmission using digital techniques. |
| DSSS | Direct Sequence Spread Spectrum. A transmission technique that uses a pseudo-random, noise-like modulation code to widen the spectrum of the transmitted signal. |
| DTK | Desired Track |
| Duplex | The ability in a communications systems to simultaneously transmit and receive signals through a common component such as an antenna. |
| Duplex cable | A two-fiber cable suitable for duplex transmission. |
| Duplex transmission | Transmission in both directions, either one direction at a time (half duplex) or both directions simultaneously (full duplex). |
| Duplexer | A circuit or component that allows a communications system to simultaneously transmit and receive signals through a common component, such as an antenna. Such systems typically use different frequencies for the transmit and receive signals, so the duplexer is often a pair of filters, each tuned to pass the desired signal frequency and reject the other signal frequency. |
| Duroid | A commercially available product used to make microwave printed circuit boards, especially those employing microstrip, strip line and coplanar waveguide transmission line structures. The dielectric layer of Duroid" is tightly controlled and is available with a number of different relative dielectric constants and physical thicknesses. |
| Dust Cover | An item specifically designed to cover the mating end of a connector for mechanical and/or environmental protection. |
| Duty Cycle | Maximum recommended usage (cycles) per unit of time. Alternatively, the percent of the 'on' time of a square wave in a switching power supply. |
| DWDM | dense wavelength division multiplexing |
| DWV | Dielectric Withstanding Voltage - A test voltage for a wire, cable, or insulation. |
| Dynamic Load | Output load that changes rapidly. Normally specified as both a load change value and a rate of change. |
| Dynamic Range | The power range over which a component or system functions properly. |
| Dynamic Response | Output overshoot that occurs when the converter output load is turned on/off or abruptly changed. This overshoot gives the high frequency output impedance of the converter. Also see Output Impedance. |
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