lecroy 22_LTXXX-OM-E_Glossary 电路图.pdf

LTXXX-OM-E Rev BISSUED: January2002243 GL O S S A R YO FTE C H N I C A LTE R M S AcquisitionTime: Inasample-and-holdor track-and-holdcircuit, thetimerequiredafter thesampleor track commandfor theoutput toslewthroughafull-scalevoltagechangeandsettletoits final valuewithina specifiederror band. ACSN: auto-correlationsignal-to-noise ADC: analog-to-digital converter. Aliasing: Whenever adynamic signal is synchronouslysampled, apossibilityof misunderstandingits frequency content exists. This difficultyis termed“aliasing” andoccurs whenever thesamplingrateis less than twicethe highest frequencycomponent inthesignal beingmeasured. AND: Logical designation or circuit functionmeaningthat all inputs must beintheTRUE statefor aTRUE output. Aperture Jitter: Inasample-holdor ADC, thejitter betweenthetimeof thesample(or convert)command pulseandthetimetheinput signal is actuallysampled. This jitter is usuallyduetothermal noise. It leads toan uncertaintyinthesampledamplitudeequal todeltat*dV/dt, wheredeltat is theaperturejitter, anddV/dt is therateof changeof theinput voltageat thetimeof sampling. Theterms “aperturejitter” and“aperture uncertainty” areoftenusedinterchangeably. Aperture Uncertainty: Inasample-holdor ADC, thetotal uncertaintyinthetimeof thesample(or convert) commandpulseandthetimetheinput signal is actuallysampled, duetoall causes includingnoise, signal amplitude-dependent delayvariation(as inaflashADC), temperature, etc. Oftenusedinterchangeablywith “aperturejitter,” but “apertureuncertainty” is themoreinclusiveterm. Area: InatimedomainDSO waveform measurement, areais thesum of thesampledvalues betweenthe cursors times thedurationof asample. Artifact Rejection: Usedinsummedaveragingtoexcludewaveforms that haveexceededthedynamic rangeof therecordingsystem. Automatic Setup: Inanoscilloscope, automatic scalingof thetimebase, trigger, andsensitivitysettings. Provides astabledisplayof repetitiveinput signals. Average: SeeMeanValue, SummedAveragingandContinuous Averaging. AWG: arbitrarywavegenerator Bandwidth: Innormal use, thefrequencyrangeover whichthegainof anamplifier or other circuit does not varybymorethan3 dB. BER: SeeBit Error Rate. Binning: A techniquefor combiningpoints inahistogram tobecompatiblewiththeresolutionof thedisplay device. Bit: Anabbreviationof “binarydigit,” oneof thetwonumbers, 0 and1, usedtoencodedata. A bit is often expressedbyahighor lowelectrical voltage. RadioFans.CN 收音机爱 好者资料库 GL O S S A R Y 244ISSUED: January2002LTXXX-OM-E Rev B Bit ErrorRate: Ratioof thenumber of bits of amessageincorrectlyreceivedtothetotal number received. CCD: ChargeCoupledDevice. Anintegratedcircuit that allows thetransfer of avariableamount of charge throughaseries of cells; ananalogshift register. CCTM: clockcertificationtest module Channel: A paththroughanarrangement of components (modules andelectrical or optical cablingor both) alongwhich signals canbesent. Clamping: Holdingacircuit point tosomereferencelevel (frequentlyground)bymeans of alow-impedance element suchas asaturatedtransistor, FET, forward-biaseddiode, relay, etc. Coherent Gain: Thenormalizedcoherent gain of afilter correspondingtoeachwindowfunctionis 1.0 (0 dB) for therectangular windowandless than1.0 for other windows. It defines theloss of signal energyduetothe multiplicationbythewindowfunction. CommonMode Range: Themaximum range(usuallyvoltage)withinwhichdifferential inputs canoperate without aloss of accuracy. CommonMode RejectionRatio: Theratio of thecommon-modeinput voltagetotheoutput voltage expressedindB. Theextent towhichadifferential amplifier does not provideanoutput voltagewhenthesame signal is appliedtobothinputs. CommonMode Signal(Noise): Thesignal (usuallynoise)that appears equallyandinphaseoneachof the differential signal conductors toground. SeeDifferential Input. Continuous Averaging: Sometimes called“exponential averaging,” thetechniqueconsists of therepeated addition, withunequal weight, of successivesourcewaveforms. Eachnewwaveform is addedtothe accumulatedaverageaccordingtotheformula: S(i,new)= N/(N+1)* S(i,old)+ 1/(N+1)* W(i) wherei = indexover all datapoints of thewaveforms; W(i)= newlyacquiredwaveform;S(i,old)= oldaccumulated average; S(i,new)= newaccumulatedaverage; N = weightingfactor (1,3,7.). ConversionCycle: Entiresequenceinvolvedinchangingdatafrom oneform toanother, e.g.,digitizingan analogquantity, changingbinarydatatoBCD, etc. Crosstalk: Unwantedcouplingof asignal from onechannel toanother. Cursor: A visiblemarker that identifies ahorizontal or vertical position, or both, onan oscilloscopedisplay. LeCroyDSOs offer “waveform riding” cursors that convenientlygiveboth thehorizontal andvertical values without selectingoneor theother. DAC: digital-to-analogconverter Data Logger: Aninstrument that accepts input signals (usuallyslowanalog), digitizes them, andstores the results inmemoryfor later readout. Thedigital equivalent of astrip-chart recorder. DC: Direct current. Normallymeans avoltageor current that remains constant. DC LevelShift: A changeinthenominal DC voltagelevel present inacircuit. DC Offset: SeeDC Level Shift. This term mayimplythat theshift is intentional, for example, adjustablebya control knob. RadioFans.CN 收音机爱 好者资料库 TechnicalTerms LTXXX-OM-E Rev BISSUED: January2002245 DC Overload: Anoverloadsignal of longdurationcomparedtothenormal input pulsewidthor dutyratioof acircuit. Dead Time: Inadigital oscilloscope, thedeadtimeis thetimefrom theendof oneacquisition of datatothe start of thenext acquisition. Decimation: Theprocess of reconstructingasourcewaveform withareducednumber of datapoints byusing onlyeverynthdatapoint, wherenis aninteger. DifferentialInput: A circuit withtwoinputs that is sensitiveto thealgebraic differencebetweenthetwo. DifferentialLinearity: A term ofteninappropriatelyusedtomeandifferential non-linearity. DifferentialNon-Linearity: 1. Thepercentagedeparturefrom theaverageof theslopeof theplot of output versus input from theslopeof areferenceline; 2. Thepercentageof variationin ADCs or TDCs from the meanof theanalog(or time)widthof anysingledigital step. It is usuallymeasuredbydrivingtheinput witha largenumber of random amplitudepulses andthenmeasuringtherelativenumber of events ineachdigital bin. DifferentialOutput: A circuit withtwo outputs supplyingonenormal andonecomplementarylevel of output signal. DifferentialPulses: Twooppositepolaritypulses coincident in time. Dithering: Typicallyusedwhenaveragingsignals (which havelownoisecontent)toimprovevertical resolution anddecreasetheeffects of anADCs non-linearities. Thetechniqueapplies different offsets toeachincoming waveform toensurethesignal is not always digitizedbythesameportionof theADC. Theoffsets must be subtractedfrom therecordedsignals beforebeingincludedinthesummedaverage. DigitalFiltering: Themanipulation of digital datatobothenhancedesirableandtoremoveundesirable aspects of thedata. Dropout Trigger: A trigger that occurs if theinput signal drops out for atimeperiodlonger thanapreset amount (between25 ns to20 s onsomeLeCroyDSOs). This is veryuseful for triggeringonmicroprocessor crashes, networkhangups, bus contentionproblems or other phenomenawhereasignal stops occurring. DutyCycle: A computedvalueindigital scopes representingtheaveragedurationabovemidpoint valueas a percentageof theperiodfor timedomainwaveforms. Dynamic Range: Theratioof thelargest tosmallest signal that canbeaccuratelyprocessedbyamodule. Dynamic RAM (DRAM): A random access memoryinwhichtheinternal memorymust berefreshed periodically. ECL: Emitter-coupledlogic, anunsaturatedlogic performedbyemitter-coupledtransistors. Usually, ECL LOGICAL 1 = 1.6 V andLOGICAL 0 = 0.8 V. EMI: Electromagnetic interferencecausedbycurrent or voltageinducedintoasignal conductor byan electromagnetic field. ENBW (Equivalent Noise Bandwidth): For afilter associatedwitheachfrequencybin, ENBW is the bandwidthof anequivalent rectangular filter (havingthesamegainat thecenter frequency)that wouldcollect thesamepower from awhitenoisesignal. RadioFans.CN 收音机爱 好者资料库 GL O S S A R Y 246ISSUED: January2002LTXXX-OM-E Rev B Enhanced Resolution(ERES): A facilityinLeCroyDSOs toincreasetheamplituderesolutionof single-shot waveform measurements. This technique, whichapplies digital filteringtoachieveresolutionenhancement at a reducedbandwidth, is optimum whenthesamplingrateof theinstrument exceeds that requiredfor theinput signal bandwidth. For repetitivesignals, either ERES or Signal Averaging, or both, can beusedtoachieve higher resolutionwithsubstantiallysmaller loss of bandwidththanfor single-shot signals. Envelope: Themaximum, minimum, or maximum andminimum values of asequenceof measured waveforms. InLeCroyDSOs, thenumber is programmablefrom 1 to106. EPROM: Erasable, programmableread-onlymemory. Anintegratedcircuit memoryarraythat is madewitha patternof either all logical zeros or ones andhas apatternwrittenintoit bytheuser withaspecial hardware program. Equivalent Time Sampling (EQT): (Alsoknownas ETS.)A means of exploitingmultipleacquisitions of a repetitivesignal toincreasetheusablebandwidthof adigitizer bymakingit appear to samplemorerapidlythan its maximum single-shot samplerate. Works onlywith stable, repetitivesignals. Extrema: Thecomputationof awaveform envelope, byrepeatedcomparison of successivewaveforms, of all maximum points (roof)andall minimum points (floor). Whenever agivendatapoint of thenewwaveform exceeds thecorrespondingmaximum valueintheroof record, it is usedtoreplacetheprevious value. Whenever agivendatapoint of thenewwaveform is smaller thanthecorrespondingfloor value, it is usedto replacetheprevious value. Falltime: Unless otherwisedefined, thetimerequiredfor apulsetogofrom 90 % to10 % of full amplitude. Canalsorefer generallytothetrailingedgeof apulse. Fast FourierTransform(FFT): Insignal processingapplications, anFFT is amathematical algorithm that takes adiscretesourcewaveform, definedover npoints, andcomputes ncomplexFourier coefficients, which areinterpretedas harmonic components of theinput signal. For a“real” sourcewaveform (imaginarypart equals 0), therearen/2 independent harmonic components. Feedthrough: Anunwantedsignal that passes aclosedgateor disabledinput. FFT: SeeFast Fourier Transform. FFT FrequencyBins: A Fast Fourier Transform (FFT)corresponds toanalyzingtheinput signal withabank of n/2 filters, all havingthesameshapeandwidth, andcenteredat n/2 discretefrequencies. Eachfilter collects thesignal energythat falls intotheimmediateneighborhoodof its center frequency, andthus it canbesaidthat therearen/2 “frequencybins.” Thedistance, inHz, betweenthecenter frequencies of twoneighboringbins is always: deltaf = 1/T, whereT is thedurationof thetime-domainrecords inseconds. Thenominal widthof binis equal todeltaf. FFT FrequencyRange: Therangeof frequencies computedanddisplayedinanFFT is 0 Hz totheNyquist frequency. FFT FrequencyResolution: Inanarrowsense, thefrequencyresolutionis equal tothebin width, deltaf. That is, if theinput signal changes its frequencybydeltaf, thecorrespondingspectrum peakwill bedisplaced bydeltaf. For smaller changes of frequency, onlytheshapeof thepeakwill change. However, theeffective frequencyresolution(i.e., theabilitytoresolvetwo signals whosefrequencies arealmost thesame)is further TechnicalTerms LTXXX-OM-E Rev BISSUED: January2002247 limitedbytheuseof windowfunctions. TheENBW valueof all windows other thantherectangular is greater thandeltaf (i.e., greater thanthebinwidth). FFT Numberof Points: FFT is computedover thenumber of points (Transform Size)whoseupper bound is thesourcenumber of points. FFT generates spectrahavingn/2 output points. FFT TotalPower: Areaunder thepower densityspectrum infrequency-domainmeasurements. FIFO: First-in, first-out shift registers (sometimes calledfirst-in, first-out memory). Filter: Anelectronic circuit or digital datamanipulationroutinethat either enhances desirableor removes undesirableaspects of ananalogwaveform or its digital representation. Filters areusedtoblockspecific frequencycomponents from passingthroughacircuit, tolinearizeotherwiseidentical components (suchas CCDs)usedinacommoncircuit, or to perform waveform integration, differentiation, or smoothing, just to nameafewtypes. FlashADC: A veryfast analog-to-digital converter, usuallyconsistingof alargeset of fast comparators and associatedlogic, inwhichtheanalogsignal simultaneouslyis comparedto2n 1 different referencevoltages, wherenis theADC resolution. Alsocalledaparallel converter. Floor: Therecordof points that makethebottom (or minimum)of anenvelopecreatedfrom asuccessionof waveforms. FWHM: Full-WidthHalf Maximum. Thewidthof apulseor waveform at 50 % amplitudeusedtomeasure thedurationof asignal. Gate: 1. A circuit element usedtoprovidealogical function(e.g., AND, OR); 2. Aninput control signal or pulseenablingthepassageof other signals. Glitch: A spikeor short-timedurationstructural aberrationonan otherwisesmooth waveform that is normally characterizedbymoregradual amplitudechanges. Indigital electronics, wherethecircuit under test uses an internal clock, aglitchcanbeconsideredtobeanypulsenarrower thantheclockwidth. GlitchTrigger: A trigger on pulsewidths smaller thanagivenvalue. Ground Loop: A longgroundconnectionalongwhichvoltagedrops occur dueeither toheavycircuit current or external pick-up, withtheresult that circuit elements referredtodifferent points alongit operateat different effectivegroundreferences. HF Sync: Reduces thetrigger ratebyincludingafrequencydivider inthetrigger path, enablingtheinput trigger ratetoexceedthemaximum for repetitivesignals. Histogram: A graphical representation of datasuchthat thedatais dividedintointervals or bins. Theintervals or bins arethenplottedonabar chart wheretheheight is proportional tothenumber of datapoints contained ineachinterval or bin. Holdoff byEvents: Selects aminimum number of events betweentriggers. Anevent is generatedwhen the trigger sourcemeets its trigger conditions. A trigger is generatedwhen thetrigger conditionis met after the selectednumber of events from thelast trigger. Thehold-off byevents is initializedandstartedoneach trigger. GL O S S A R Y 248ISSUED: January2002LTXXX-OM-E Rev B Holdoff byTime: Selects aminimum timebetweentriggers. A trigger is generatedwhenthetrigger condition is met after theselecteddelayfrom thelast trigger. Thetimingfor thedelayis initializedandstartedoneach trigger. HPGL: Hewlett-PackardGraphics LanguageFormat; Hewlett-PackardCompany. Hybrid Circuit: A small, self-contained, high-densitycircuit element usuallyconsistingof screenedor depositedconductors, insulatingareas, resistors, etc., with weldedor bondedcombinations of discretecircuit elements andintegratedcircuit chips. IC: IntegratedCircuit. A self-contained, multiple-element circuit suchas amonolithic or hybrid. IntegralLinearity: A term oftenusedinappropriatelytomeanintegral non-linearity. IntegralNon-Linearity: Deviation of ADC responsefrom anappropriatestraight linefit. The