ELECTRONIC GLOSSARY
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ELECTRONIC GLOSSARY |
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TECHNICAL TERMS A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A 'A' filtering - mimics human ear's frequency response ADC (analogue-to-digital converter) - electronic device which converts an analogue voltage to a digital number Aliasing - undesired modulation which distorts the baseband signal, caused by under-sampling, eg by ADC's in oscilloscopes or telecoms applications AM (amplitude modulation) - the amplitude of a carrier wave is modified by an analogue or digital signal which is to be transmitted (see also FM and PM) AMI (alternate mark inversion) - a method of transmitting binary digits where successive marks, equal in magnitude, normally alternate between positive and negative polarity AMPS (american mobile phone standard) - US analogue cellular radio standard Analogue - direct representation of data, such as a human voice, by a continuously varying electrical signal ANSI - American National Standards Institute ASCII (american standard code for information interchange) - represents text by binary numbers ASIC - application-specific integrated circuit Asynchronous data - transmission of digital data without locking the sender and receiver's clocks ATM (asynchronous transfer mode) - a flexible high-bandwidth networking standard which uses cell-relay rather than packet switching or direct connection and avoids the need to synchronise the sender and receiver Attenuation - reduction of signal strength, measured in dB; negative gain AU (administrative unit) - high order SDH virtual carrier with pointer attached, ready for STM-N transmission AUG (administrative unit group) - SDH AU, provides compatibility with SONET Autonomy Time - length of time that an uninterruptible power supply can maintain full output when the mains input is removed B3ZS/B6ZS (bipolar 3/6 zero substitution) - coding format where strings of 3 or 6 consecutive zeros are replaced by a shorter code Bandwidth - the difference between the lowest and highest frequency of a communications channel, used as a measure of its data carrying capacity Band III - UK trunked PMR using 420MHz frequency band Baseband signal - the signal input or output from a modulated transmission system, such as a human voice or computer data stream Baud rate - the data transmission rate of a serial communications link, expressed in bits per second (b/s) BCCH (broadcast control channel) - GSM signalling feature BER - bit error rate Binary - base-two number system widely used in digital and computer systems; it uses two symbols, 0 and 1, often represented by two voltage levels Bit (binary digit) - the smallest unit of information in a binary system; a bit can have value 0 or 1 BLER (block error rate) - BER modified to count errors in transmitted blocks of bits BS EN ISO 9000 - quality systems standard (formerly BS 5750) Buffer - storage device used to accommodate different rates of data flow or event timing when transmitting data from one device to another Burst mode - transmission of a short stream of data, often triggered by handshaking; in a high-speed network, the address of the data is sent, followed by the data itself Bus - multi-wire electrical connection between devices, used in computers (eg AT bus and EISA bus), test equipment (eg IEEE 488), and mains systems (ie 3 phase and neutral) Byte - eight bits of data, which form a digital 'word'; computer memory is arranged as an array of one or more bytes C (container) - PDH data stream used for SDH transmission Carrier - often a high frequency sine wave to which modulation is added to transmit information Cat 5 - standard for structured premises wiring, with a frequency response up to 100MHz CCITT - Renamed the ITU-TS CDMA (code division multiple access) - radio access method where users are allocated a unique code sequence within a spread-spectrum communication system CMI (coded mark inversion) - a more complex version of NRZ which relies on transitions to indicate binary 1 or 0, used for higher rate PDH links CMRR (common-mode rejection ratio) - a measure of a circuit's ability to reject signals common to both input connections, usually expressed in dB Compander (compressor-expander) - variable gain device which automatically adjusts a signal level to maintain it within defined limits Coupler - an optical or electrical device which splits or combines signals CRC (cyclical redundancy check) - an extra bit is added to a set of data so the sum of the digits is odd (or even); enables detection of single errors in storage or transmission CRT (cathode ray tube) - display used in monitors and televisions Crest factor - the ratio of the peak voltage of an AC waveform to its RMS value Crosstalk - the unwanted transfer of a signal from one circuit to another DAC (digital-to-analogue converter) - electronic device which converts a digital number into a corresponding analogue voltage or current DASS 2 (digital access signalling system) - UK predecessor to ISDN DAT - digital audio tape dB (Decibel) - logarithmic ratio of two signals (see Formulae & Conversion) dBc/Hz - noise density in a 1Hz equivalent bandwidth of a modulation system, relative to the carrier amplitude dBm - absolute measure of signal power, where 0dBm equals 1mW DCS1800 (digital cellular standard at 1800MHz) - GSM at twice the frequency DDCMP (digital data communications message protocol) - proprietary computer-to-computer communications protocol DECnet - proprietary network architecture that works across all Digital Equipment computers; uses a peer-to-peer approach Digital - representation of data by the nearest binary number Disassembler - software tool which allows on-line evaluation and debugging of computer hardware and software Distortion - undesired changes to a waveform DOS - PC disk operating system DPNSS (digital private network signalling system) - UK telecoms protocol for private networks DSP (digital signal processor) - digital implementation of a signal filter DS1 (digital signal 1) - T1 transmission standard (1.544Mb/s) DS3 (digital signal 3) - T3 transmission standard (44.736Mb/s) DTMF (dual-tone multiple frequency) - signalling system generated by pushbutton telephones DVB - digital video broadcasting Duplex - simultaneous, two-way independent data transmission Dynamic range - the ratio of the largest signal level a circuit can handle to the smallest signal level it can detect (usually its noise level), usually expressed in dB EBCDIC (extended binary coded decimal interchange code) - eight bit character code used primarily in IBM computers EEPROM (electrically erasable programmable read-only memory) - ROM that can be erased with an electrical signal and reprogrammed EFS (error free seconds) - similar measure to BER and BLER EIA (Electronic Industries Association) - a consultative group of manufacturers for standardising electronic equipment EISA (extended industry standard architecture) - 32-bit adaptation of the 8/16-bit buses originally developed by IBM EMC (electromagnetic compatibility) - definition of the acceptable limits for electromagnetic emissions by an electronic device, and how much electromagnetic interference it should tolerate EPLD - electronically programmable logic device EPROM (erasable programmable read-only memory) - ROM that can be erased, usually by exposure to ultraviolet light, and reprogrammed ESD - electrostatic discharge Ethernet - widely used LAN transmission network, based on a bus network topology, runs at 10 or 100Mb/s ETSI - European Telecommunications Standards Institute External trigger - a voltage pulse from an external source that triggers an event F FDDI (fibre distributed data interface) - ANSI standard for fibre optic LAN, based on 100Mb/s logical ring topology, using token-passing access control FDM (frequency division multiplexer) - a device which divides up the available bandwidth of a transmission path into separate communications channels FDMA (frequency division multiple access) - radio access method where users are allocated an available frequency channel on request FFT - fast fourier transform - mathematical method of analysing the frequencies in a measured waveform FM (frequency modulation) - the frequency of a carrier wave is modified by an analogue or digital signal which is to be transmitted (see also AM and PM) Frequency - the number of times a signal recurs during a set period, measured in Hertz (Hz) FSK (frequency shift keying) - a form of FM in which the frequency of the carrier is modulated, or keyed, by a digital signal G Gain - the factor by which a signal is amplified, sometimes expressed in dB GAL - gate array logic Glitch - a transient pulse in a digital circuit, narrower than the system's clock width GMSK (gaussian minimum shift keying) - digital modulation scheme designed to minimise required bandwidth, used in GSM systems GPIB (general-purpose interface bus) - alternative name for IEEE 488 GSM - pan-European digital cellular standard GUI - graphical user interface G.703 - cabling electrical specifications and line codes used by digital transmission interfaces G.704 - specification for the functional characteristics of inter-network interfaces G.732 - characteristics of A -law PCM multiplex equipment, specifying frame alignment loss, jitter, alarm indications and power loss G.821 - performance criteria for digital connections, defines allowable error rates and locations G.823 - specification for jitter and wander allowable on international digital connections using A-law systems Handshaking - method by which data is exchanged between devices only when each device has signalled that it is ready Hayes command set - de-facto standards for controlling modem dialling operations and setting operational parameters HDB2/3 (high density bipolar of order 2/3) - coding system for providing AMI with extra transitions to allow timing recovery HDLC (high-level data-link control) - set of ISO protocols for carrying data over a link with error and flow control HDTV - high definition television HP-GL (Hewlett-Packard graphics language) - set of easy-to-understand mnemonic commands for controlling functions such as pen movement, character generation, and axis printing HP-IL (Hewlett-Packard interface loop) - serial interface designed for low cost battery operable systems HP-IB (Hewlett-Packard interface bus) - alternative name for IEEE 488, a parallel interface designed by HP IC - integrated circuit, also known as a 'chip' IEEE (Institute of Electrical and Electronic Engineers) - US professional body also involved in electronic standards IEEE 488 - high-speed parallel communications interface, used extensively in Test & Measurement equipment IEEE 802.3 - IEEE standardisation of Ethernet LAN protocol IEEE 802.5 - IEEE standardisation of IBM's Token-Ring LAN protocol IP- internet protocol IrDA-1 - infra-red computer interface I/O - input/output IRIG WB1&2 (inter range instrumentation group wideband 1&2) - standard for recording, WB1 is DC to 20kHz and WB2 is DC to 125kHz ISA (industry standard architecture) - 8/16-bit bus standard used in PCs ISDN (integrated services digital network) - public telecoms network standard for transmitting voice, data and digital images such as videoconferencing ISO - International Standard Organisation ITU (International Telegraphic Union) - part of the United Nations which deals with telecoms ITU-TS (ITU - Telecommunication Standards) - global telecoms standards body, formerly known as CCITT Jitter - instability of a signal, effectively a form of FM or PM JPEG (Joint Photographic Experts Group) - standard for digital compression of graphic-image files LAN (local area network) - datacoms network that links computers into a network over a limited geographical area, allows users to communicate and share resources LCC - leadless chip carriers LO - local oscillator Microlease plc - exceptional service organisation used to satisfy electronic test equipment rental needs MNP 4, 5, 10 - data compression standards for modems Modulation - controlled variation of amplitude, frequency, and/or phase of a carrier wave in order to transmit a message MPEG (Motion Pictures Experts Group) - standard for digital compression of video recordings MPT1327 - UK analogue trunked radio standard Multiplexer (mux) - device which outputs one of a number of input signals as commanded by a control input NAMAS (National Accreditation of Measurement and Sampling) - the standard to which UKAS accredits calibration and testing laboratories NATEL - Swiss analogue radio standard NEXT (near-end crosstalk) - interference between conductors of a cable when used in a LAN application NICAM (near instantaneous companded audio multiplex) - stereo TELEVISION audio broadcasting standard Noise - undesirable electrical signal NRZ (non-return to zero) - two-state code which represents binary symbols simply by high and low signal levels NTSC (National Television System Committee) - US standard for analogue colour television broadcasting O/C - open circuit PAL (phase alternation by line) - European standard for analogue colour television broadcasting Parallel interface - datacoms interface in which data is transmitted simultaneously along several wires Parity bit - a bit that is set at 0 or 1 in a data word to ensure that the total number of bits is even or odd, as desired PBX (private branch exchange) - private telephone switch connected to a public network PCL5 - printer language PCM (pulse code modulation) - quantisation of an analogue signal, such as a voice link, for digital transmission PCM30 / 31 - PCM framing standard PCS (personal communication system) - US digital cellular standard similar to DCS1800 PCMCIA (Personal Computer Memory Card International Association) - physical and electrical standard for PC cards, such as memory, modems and interfaces PDC - personal digital cellular PDH (plesiochronous digital hierarchy) - a form of TDM where dummy information is added to synchronise data streams of slightly different speeds, ready for transmission over a higher-speed link Period - a defined length of time PF (power factor) - a measure of the phase alignment of voltage and current in an AC power system PGA - pin grid array Phase noise - short-term, random phase variations of an RF signal resulting from electrical noise within the signal generator, usually expressed in dBc/Hz Ping - TCP/IP function for confirming connection to a remote IP address PLCC - plastic leaded chip carriers PM (phase modulation) - the phase of a carrier wave is modified by an analogue or digital signal which is to be transmitted (see also AM and FM) PMR (private mobile radio) - wide area mobile radio system used by closed group organisations such as utilities and emergency services POCSAG - pager encoding format Post Script - printer language ppm - parts per million PQFP (plastic quad flat pack) - integrated circuit package PRBS - pseudo-random binary sequence PROM (programmable read-only memory) - non-volatile memory chip which can be programmed (once) with an electrical signal PSTN (public switched telephone network) - otherwise known as the dial-up telephone network PVC (permanent virtual circuit) - ATM optimisation standard PWM (pulse width modulation) - the pulse width of a square wave is modified by an analogue or digital signal which is to be transmitted (see also AM, FM and PM) RAM (random access memory) - fast memory chip which retains stored information only while power is applied Raster - constant scanning pattern of an electron beam on a CRT display which forms images by turning the beam on and off at appropriate times Real time - data is processed as it is acquired, rather than being stored and processed later Refractive index - ratio of the speed of light in a vacuum to the speed of light in a material Resolution - the smallest signal increment that can be detected by a measurement system, expressed in bits, proportions, or as percentage of full scale reading; resolution in a video system is the amount of detail in a graphic image RF - radio frequency RISC (reduced instruction set computing) - computing architecture in which fewer processor instructions are defined so that most can be performed in a single processor cycle, improving computing efficiency
Rise time - time required for the leading edge of a pulse to rise from 10% to 90% of its final value RMS (root mean square) - a form of averaging ROM (read only memory) - memory chip used for permanently recorded computer programs and data RS232 - serial interface standard RS423 - serial interface for cables longer than the RS232 24m limit RS449 - physical interface standard for RS422 and RS423 signals RZ (return to zero) - two-state code in which binary 1 symbols are represented by a pulse rather than a level, ie the signal returns to zero for the second part of the system clock cycle SACCH (slow associated control channel) - GSM signalling feature SCM - suppressed carrier modulation SCSI (small computer standard interface) - interface standard for connecting intelligent peripherals such as hard disks, printers, and optical disks; pronounced 'scuzzy' SDH (synchronous digital hierarchy) - ITU-TS standard for transmission of synchronously multiplexed tributary signals; aligned with SONET from 155Mb/s (STM-1) and higher SDLC (synchronous data link control) - the primary data link protocol used in SNA networks SECAM (séquential couleur à mémoire) - French standard for analogue colour television broadcasting SEL - sound exposure level SELCALL (selective calling) - analogue PMR feature which uses tone encoding/decoding Serial interface - datacoms interface in which data is transmitted bit by bit down a single pair of wires SIM Card (subscriber identity module) - used in digital cellular mobile phones to program data such as the unit's telephone number and home network operator SINAD - ratio of combined signal plus noise and distortion, to noise and distortion, expressed in dB Single-mode fibre - an optical fibre that supports only one mode of light propagation Slew rate - maximum rate of change of an amplifier's output when operated within its linear region SMD - surface mount device SNA (systems network architecture) - IBM's proprietary standard for communication between hardware devices SNAP (subnetwork access protocol) - an IP which implements logical link control and enables non-standard higher layer protocols SNMP (simple network management protocol) - originally designed to manage TCP/IP networks, now used more widely SNR (signal-to-noise ratio) - the ratio of overall RMS signal level to RMS noise level in dB SONET (synchronous optical network) - US standard for transmission of synchronously multiplexed tributary signals SPL - sound pressure level SSB (single side band) - radio communication where half of the modulator output is transmitted to reduce channel bandwidth and transmitted power SS7 (signalling system number 7) - ITS digital transmission protocol for interconnection of telephone exchanges Strain gauge - a transducer which changes its resistance in proportion to the applied force STM (synchronous transport module) - SDH frame into which a 'payload' of data is multiplexed for transmission; 'overhead' space is also allowed for network control SVC (switched virtual circuit) - ATM optimisation standard Synchronous data transmission - information is transmitted at predictable times usually defined by a clock signal TCP/IP (transmission control protocol / internet protocol) - set of protocols that allows sharing of applications among PC's, host computers and workstations in a high-speed communications environment TDD (time division duplex) - bi-directional radio access method where the same frequency is used for both transmit and receive modes TDM (time division multiplexer) - multiplexer which combines tributary channels by interleaving the data streams TDMA (time division multiple access) - radio access method where users are allocated an available time slot within a frequency channel on request Thermocouple - temperature transducer formed from two dissimilar metals, which produce a small voltage dependent on the temperature Time base - calibrated sweep generator used to control displays, such as oscilloscopes, or the repetitive variation of a measurement parameter, for instance in network analysers and sweep generators TIMS - transmission impairment measurement standard THD (total harmonic distortion) - the ratio of the sum of harmonic distortion signals to the overall RMS signal, in dB or percent Token-Ring Network - widely used LAN transmission network in which access is controlled by passing a token to each station around the network in a predetermined sequence TOP (technical and office protocol) - Boeing proprietary teletext standard Transconductance - the ratio of the incremental change in the output current of an amplifier to the incremental change of input voltage Transducer - a device which responds to a physical stimulus (heat, light, sound, pressure, motion, flow, etc), and produces a corresponding electrical signal Transceiver - a combined transmitter and receiver Trigger - a stimulus which starts a measurement or display function which then continues under its own control TU (tributary unit) - SDH virtual carrier with pointer attached TUG (tributary unit group) - SDH tributary unit with several TUs interleaved ready for a higher order virtual carrier Twisted pair - two insulated copper conductors that are wound around each other to reduce the effects of induced electrical noise UKAS - United Kingdom Accreditation Service UNI (user network interface) - ATM standard VAR (volt-ampere reactive) - the out-of-phase component of an AC power system which does no useful work VC (virtual carrier) - PDH container with path overhead ready for SDH TU or AU VCI (virtual channel identifier) - ATM standard VCO - voltage controlled oscillator VDEW - German digital PMR signalling system VPI (virtual path identifier) - ATM standard VPT - teletext format VSWR (voltage standing wave ratio) - the ratio of maximum to the minimum voltage along a transmission line, caused by reflections V Series - ITU-TS recommendations governing data transmission over analogue telephone lines; the series includes: V.21 - 300b/s duplex modem, similar to RS422 V.22 - 1,200b/s duplex modem V.22bis - 2,400b/s duplex modem V.23 - 600 or 1,200b/s FSK modem V.24 - interchange circuits, similar to and compatible with RS232 V.32 - up to 9,600b/s modem V.32bis - up to 14.4kb/s modem V.35 - 34-pin 48kb/s interface V.36 - 4-wire datacoms at speeds of 48kb/s and higher V.42 - error correction protocol V.42bis - data compression technique for use with V.42 WAN (wide area network) - datacoms network covering a wider geographical area than a LAN using telecoms links Waveguide - transmission line consisting of a hollow conductor used to guide microwaves from one end to the other White Noise - broadband pseudo-random signal with uniform power in each frequency band Word - the standard number of bits that a processor or memory manipulates at one time; computers and microcontrollers typically use 8, 16 or 32-bit words XNS (Xerox network systems) - a proprietary peer-to-peer protocol developed by Xerox, incorporated into several LAN schemes X-ON/X-OFF (Transmitter On / Transmitter Off) - control characters used for flow control instructing a terminal to start transmission (X-ON) and stop transmission (X-OFF) X Series - ITU-TS recommendations governing data transmission over public data networks; the series includes: X.20 - asynchronous communications interface for use over PSTN X.21 - synchronous communications interface for use over PSTN X.25 - packet-switched data interface ZIF (zero insertion force) sockets - socket for an integrated circuit package which reduces the chances of damage to its pins ZVEI1 - German digital PMR signalling standard |