EMI Unit II

Signal Generators and Analyzers

1. UNIT II
SIGNAL ANALYZERS AND
SIGNAL GENERATORS
By –
GVNSK Sravya
Asst. Professor
ECE Dept.

2. Contents
Signal Generators
AF Signal Generators
RF Signal Generators
Sweep Frequency Generators
Pulse and Square wave Generators
Function Generators
Arbitrary Waveform Generator
Video Signal Generators
Signal Analyzers
AF, HF Wave Analyzers
Harmonic Distortion Analyzers
Heterodyne wave Analyzers
Spectrum Analyzers
Power Analyzers
Capacitance-Voltage Meters
Oscillators.

3. Signal Generators
Asignalgeneratorisanelectronicdevicethatgenerates
repeatingornonrepeatingelectronicsignalsineitherthe
analogorthedigitaldomain.
Itisgenerallyusedindesigning,testing,troubleshootingand
repairingelectronicdevices.

4. Contd…
Itmustbecapableofproducingstablesignalsoverawide
rangeoffrequenciesfromafewHz.toevenGHz.Ranges.
Amplitudemustbevariableandattenuatorsareusually
providedtochangetheamplitude.Theamplitudemustalso
bevariablefromalowvaluetoahighvalue.

5. Contd…
Signalsourcecanbebroadlyclassifiedasfollows
(i)Fixed(ii)Variable
Infixedsignalgenerators,theamplitudeofthewaveformor
frequencyorbothmaybefixed.
InVariabletype,theamplitudeofthewaveformcanbe
variedfrommillivoltstovoltsandthefrequencyisalso
variableoverawiderange.

6. Considerations in choosing Signal Generator
Thefollowingfactorsmustbeconsideredinselectingor
comparingsignalgenerators.
1.FrequencyRange
2.OutputVoltage
3.Resolution
4.Accuracy
5.Frequencystability
6.Amplitudestability
7.Distortion

7. Basic Standard Signal Generator(Sine Wave)
Thesinewavegeneratorrepresentsthelargestsignalcategory
ofsignalgenerator.
ItcoversafrequencyrangefromfewHz.ToGHz.

8. Contd…
Simplesinewavegeneratorconsistsoftwoblocks
i.e.,anoscillatorandanattenuator.
Theaccuracyofthefrequency,stabilityand
freedomfromdistortiondependonthedesignof
oscillator,whiletheamplitudedependsonthe
designofattenuator

9. AF Sine Wave and Square Wave Generator
The block diagram of an AF sine and square wave generator is
shown below.

10. Contd…
Awienbridgeoscillatoristhebestfortheaudio
frequencyrange.
Thefrequencyofoscillationscanbechangedby
varyingthecapacitanceintheoscillator.
Thefrequencycanalsobechangedinstepsby
switchinginresistorsofdifferentvalues.

11. Contd…
TheoutputoftheWienbridgeoscillatorgoestothe
functionswitch.
Thefunctionswitchdirectstheoscillatoroutput
eithertothesinewaveamplifierortothesquare
waveshaper.
Attheoutput,wegeteitherasquareorsinewave.
Theoutputisvariedbymeansofanattenuator.

12. Contd…
Theinstrumentgeneratesafrequencyrangingfrom
10Hzto1MHz,continuouslyvariablein5
decadeswithoverlappingranges.
Theoutputsinewaveamplitudecanbevariedfrom
5mVto5V(rms).Theoutputistakenthrougha
push-pullamplifier.Forlowoutput,theimpedance
is600Ω.

13. Contd…
Thesquarewaveamplitudescanbevariedfrom0
—20V(peak).Itispossibletoadjustthe
symmetryofthesquarewavefrom30—70%.The
instrumentrequiresonly7Wofpowerat220V—
50Hz.

14. Contd…
Thefrontpanelofasignalgeneratorconsistsofthe
following.
1.FrequencyselectorItselectsthefrequencyin
differentrangesandvariesitcontinuouslyina
ratioof1:11.Thescaleisnon-linear.
2.FrequencymultiplierItselectsthefrequency
rangeover5decades,from10Hzto1MHz.
3.AmplitudemultiplierItattenuatesthesinewavein
3decades,x1,x0.1andx0.01.

15. Contd…
VariableamplitudeItattenuatesthesinewave
amplitudecontinuously.
SymmetrycontrolItvariesthesymmetryofthe
squarewavefrom30%to70%.
AmplitudeItattenuatesthesquarewaveoutput
continuously.
FunctionswitchItselectseithersinewaveor
squarewaveoutput.

16. Contd…
Output available This provides sine wave or square
wave output.
SyncThis terminal is used to provide
synchronization of the internal signal with
anexternal signal.
On-Off Switch

17. RF or Standard Signal Generator
Astandardsignalgeneratorproducesknownand
controllablevoltages.
Itisusedaspowersourceforthemeasurementof
gain,signaltonoiseratio(S/N),bandwidth,
standingwaveratioandotherproperties.
Itisextensivelyusedinthetestingofradio
receiversandtransmitters.

18. Contd…
Theinstrumentisprovidedwithameansof
modulatingthecarrierfrequency,whichis
indicatedbythedialsettingonthefrontpanel.
Themodulationisindicatedbyameter.
TheoutputsignalcanbeAmplitudeModulated
(AM)orFrequencyModulated(FM).

19. Contd…
Modulationmaybedonebyasinewave,square
wave,triangularwaveorapulse.

20. Contd…
The carrier frequency is generated by a very stable RF
oscillator using an LC tank circuit, having a constant
output over anyfrequency range.
The frequency of oscillations is indicated by the
frequency range control and the vernier dial setting.
AM is provided by an internal sine wave generator or
from an external source.

21. Contd…
Modulation is done in the output wide band amplifier
circuit. This amplifier delivers its output, that is,
modulation carrier, to an attenuator.
The attenuator helps in selecting proper range of
attenuation and the output signal level is controlled and
the output voltage is read by an output meter.

22. Contd…
Frequency stability is limited by the LC tank circuit
design of the master oscillator.
The switching of frequency in various ranges is
achieved by selecting appropriate capacitor.

23. Contd…
Advantages
Output is stable
Output voltage can be controlled according to the requirement
Disadvantages
Frequency stability is limited due to LC tank circuit.
It takes some time to stabilize at new frequency hen the range is
changed.
Isolation between output device and RF oscillator should be
provided. It can be provided by buffer amplifiers.

24. Function Generator
FunctionGeneratorisanelectronictestequipmentused
togeneratedifferenttypesofwaveformsoverawide
rangeoffrequencies.
Someofthecommonwaveformsproducedbyfunction
generatorareSine,square,triangular,sawtoothetc.,
Thefrequencymaybeadjusted,fromafractionofa
HertztoseveralhundredkHz.

25. Contd…
Thevariousoutputsofthegeneratorcanbemade
availableatthesametime.
Forexample,thegeneratorisprovidingasquarewave
andsawtoothwaveatatime,thenthesquarewaveis
usedtoprovidethelinearmeasurementsinanaudio
systemsandsimultaneouslyprovideasawtoothto
drivethehorizontaldeflectionamplifieroftheCROto
provideavisualdisplay.

26. Contd…
Similarly,ifatriangularwaveandsinewavesare
generatedatequalfrequenciessuchthatthezero
crossingsofboththewaveformsaremadetooccurat
sametime,alinearlyvaryingwaveformisavailable.
Thisisusedinthemeasurementofphasedifferenceof
twosignals.

27. Contd…
Functiongeneratoralsohasthecapabilityofphase
lockingtoanexternalsignalsource.
Example,onefunctiongeneratormaybeusedtophase
lockasecondgeneratorandthetwooutputsignalscan
bedisplacedinphasebyoneadjustableamount.

28. Contd…
The block diagram of function generator is shown
below.

29. Contd…
Generally,thefrequencyiscontrolledbyvaryingthe
capacitorintheLCorRCcircuit.
Inthisinstrumentthefrequencyiscontrolledby
varyingthemagnitudeofcurrentwhichdrivesthe
integrator.
Theinstrumentproducessine,triangularandsquare
waveswithafrequencyrangeof0.01Hzto100kHz.

30. Contd…
Thefrequencycontrolledvoltageregulatestwocurrent
sources.
Theuppercurrentsourcesuppliesconstantcurrentto
theintegratorwhoseoutputvoltageincreaseslinearly
withtime.
Anincreaseordecreaseinthecurrentincreasesor
decreasestheslopeoftheoutputvoltageandhence
controlsthefrequency.

31. Contd…
Thevoltagecomparatormultivibratorchangesstatesat
apre-determinedmaximumleveloftheintegrator
outputvoltage.
Thischangecutsofftheuppercurrentsupplyand
switchesonthelowercurrentsupply.

32. Contd…
Thelowercurrentsourcesuppliesareversecurrentto
theintegrator,sothatitsoutputdecreaseslinearlywith
time.
Whentheoutputreachesapredeterminedminimum
level,thevoltagecomparatoragainchangesstateand
switchesontheuppercurrentsource.

33. Contd…
Theoutputoftheintegratorisatriangularwaveform
whosefrequencyisdeterminedbythemagnitudeofthe
currentsuppliedbytheconstantcurrentsources.
Thecomparatoroutputdeliversasquarewavevoltage
ofthesamefrequency.
Theresistancediodenetworkalterstheslopeofthe
triangularwaveasitsamplitudechangesandproduces
asinewavewithlessthan1%distortion.

34. Square Wave and Pulse Generator
Squareandpulsegeneratorsareelectronic
instrumentsthatareusedtogeneraterectangular
pulsesandsquarewave.
Theyareusedtotestthelogiccircuits.
Theyaremadeuseofintransientresponsetestingof
amplifiersalso.

35. Contd…
SquareandPulseGeneratorareusedasmeasuring
devicesincombinationwithaCROtodisplay
waveformeitherattheoutputoratsomespecific
pointsinthecircuitundertest.
Theyprovidebothquantitativeandqualitative
informationofthesystemundertest.

36. Contd…
Thefundamentaldifferencebetweenapulse
generatorandasquarewavegeneratorisintheduty
cycle.
Asquarewavegeneratorhasa50%dutycycle.

37. Contd…
The block diagram of a square wave and pulse
generator is shown below.

38. Contd…
Thebasiccircuitforpulsegenerationisthe
asymmetricalmulti-vibrator.
Thefrequencyrangeoftheinstrumentiscoveredin
sevendecadestepsfrom1Hzto10MHz,witha
linearlycalibrateddialforcontinuousadjustmenton
allranges.

39. Contd…
Thedutycyclecanbevariedfrom25–75%.
Twoindependentoutputsareavailable,a50Ωsourcethat
suppliespulseswithariseandfalltimeof5nsat5Vpeak
amplitudeanda600Ωsourcewhichsuppliespulseswitha
riseandfalltimeof70nsat30Vpeakamplitude.
Theinstrumentcanbeoperatedasafree-runninggenerator,or
itcanbesynchronizedwithexternalsignals.
Triggeroutputpulsesarealsoavailablewhenexternalsignals
aresynchronized.

40. Contd…
Thebasicgeneratingloopconsistsofthecurrent
sources,therampcapacitor,theSchmitttriggerand
thecurrentswitchingcircuit.

41. Contd…
Theuppercurrentsourcesuppliesaconstantcurrent
tothecapacitorandthecapacitorvoltageincreases
linearly.
Whenthepositiveslopeoftherampvoltagereaches
theupperlimitsetbytheinternalcircuitcomponents,
theSchmitttriggerchangesstate.

42. Contd…
Thetriggercircuitoutputbecomesnegativeand
reversestheconditionofthecurrentswitch.
Thecapacitordischargeslinearly,controlledbythe
lowercurrentsource.
Whenthenegativerampreachesapredetermined
lowerlevel,theSchmitttriggerswitchesbacktoits
originalstate.Theentireprocessisthenrepeated.

43. Contd…
The ratio i1/i2determines the duty cycle, and is
controlled by symmetry control.
The sum of i1and i2determines the frequency. The
size of the capacitor is selected by the multiplier
switch.
The unit is powered by an internal supply that
provides regulated voltages for all stages of the
instrument.

44. Contd…
The output waveforms of pulse and square wave are
generated below.

45. Contd…
The output of Schmitt trigger is given to trigger
output, 600 ohm output and 50 ohm output.
Trigger output differentiates the square wave output
from the Schmitt trigger, inverts the resulting pulse
and provides a positive triggering pulse.
Trigger polarity is used to provide the negative
triggering pulse to positive pulse.

46. Sweep Generator
Sweepgeneratorprovidesasinusoidaloutputvoltage
whosefrequencyvariessmoothlyandcontinuously
overanentirefrequencyband,usuallyatanaudio
rate.
Thisgeneratorproducesavaryingsweepvoltageto
drivethehorizontaldeflectionplatesofCRO.

47. Contd…
Theprocessoffrequencymodulationmaybe
accomplishedelectronicallyormechanically.
Itisdoneelectronicallybyusingthemodulating
voltagetovarythereactanceoftheoscillatortank
circuitcomponent,andmechanicallybymeansofa
motordrivencapacitor,asprovidedforinamodern
laboratorytypesignalgenerator.

48. Contd…
Theblockdiagramofasweepgeneratorisshown
below.

49. Contd…
Thefrequencysweeperprovidesavariable
modulatingvoltagewhichcausesthecapacitanceof
themasteroscillatortovary.
Arepresentativesweepratecouldbeoftheorderof
20sweeps/second.
Amanualcontrolallowsindependentadjustmentof
theoscillatorresonantfrequency.

50. Contd…
Thefrequencysweeperprovidesavaryingsweep
voltageforsynchronizationtodrivethehorizontal
deflectionplatesoftheCRO.
Thustheamplitudeoftheresponseofatestdevice
willbelockedanddisplayedonthescreen.

51. Contd…
Toidentifyafrequencyinterval,amarkergenerator
provideshalfsinusoidalwaveformsatanyfrequency
withinthesweeprange.
Themarkervoltagecanbeaddedtothesweep
voltageoftheCROduringalternatecyclesof
thesweepvoltage,andappearssuperimposedonthe
responsecurve.

52. Contd…
Theautomaticlevelcontrolcircuitisaclosedloopfeedback
systemwhichmonitorstheRFlevelatsomepointinthe
measurementsystem.
Thiscircuitholdsthepowerdeliveredtotheloadortest
circuitconstantandindependentoffrequencyandimpedance
changes.
Aconstantpowerlevelpreventsanysourcemismatchandalso
providesaconstantreadoutcalibrationwithfrequency.

53. Arbitrary waveform generator
Thearbitrarywaveformcanbedefinedasawaveformthat
doesn’thaveapredefinedshapeorcharacteristics,its
amplitudeandfrequencycanvaryinarandommanner.
Itpossessperiodicityatsometimesandnonperiodicityat
othertimes.
Itisdigitallybasedsignalsourcecapableofgeneratingany
waveformwithinpublishedlimitsofbandwidth,frequency
range,accuracyandoutputlevel.

54. Contd…
Thiswaveformcanbegeneratedbysuperimposingeither
noiseorDCoffsetvoltagesuponastandardsignalorby
introducinggapsbetweenwaveformburstsorbyperforming
variousmodulations.
Thearbitrarywaveformsareusedastestsignalstodetermine
whetherthetestequipmentisfunctioningproperlyandalsoto
detectanyfaultspresentintheequipment.

55. Contd…
Thearbitrarywaveformgeneratorisusefulfordigital
signalgeneration.
Itgeneratesaperiodicwaveformwhichtheuser
defines.
Itgenerateswaveformsbasedondigitaldatastored
inRAM.

56. Contd…
Thisdigitaldatagivestheinformationoftheconstantly
varyingvoltagelevelsofanACsignalwithoutorwithDC
content.
Inthistypeofwaveformgenerator,digitaldataisstoredin
waveformrandomaccessmemory.
InthistypeaCROisusedtomeasureawaveforminwhich
dataissampled.

57. Contd…

58. Contd…
ADACisusedtoreadbackthememorylocationsandfeeding
thedatapointstherebyreconstructingthesignalatanytime.
Themainobjectiveofarbitrarywaveformgeneratoristo
generateanarbitrarywaveformwithbetterfidelity
repetitively.
Forthis,thesamplingfrequencymustbeselectedatleast
twiceofthatofthehighestfrequencycomponentofthe
sampledsignal.

59. Contd…
Thustoproducedesiredwaveform,thesamplepointsmustbe
sufficientlylargeenough.

60. Video Signal Generator
Apatterngeneratorprovidesvideosignalsdirectly,andwith
RFmodulation,onstandardTVchannelsforalignment,
testingandservicingofTVreceivers.
Theoutputsignalisdesignedtoproducesimplegeometric
patternslikeverticalandhorizontalbars,checkerboard,cross-
hatch,dots,etc.
Itisamultiformatanaloganddigitalprecisionsignal.

61. Contd…
Thesepatternsareusedforlinearityandvideo
amplifieradjustment.Inadditiontothis,anFMsoundsignal
isalsoprovidedinpatterngeneratorsforaligningsound
sectionsofthereceiver.

62. Contd…

63. Contd…
Thegeneratoremploystwostablechainsofmultivibrators,
dividersandpulseshapingcircuits,onebelowtheline
frequencytoproduceaseriesofhorizontalbars,andanother
above15625Hztoproduceverticalbars.
Thesignalsaremodifiedintoshortdurationpulses,which
whenfedtothevideosectionofthereceiveralongwiththe
syncpulsetrain,producefinelinesonthescreen.

64. Contd…
TheMultivibratorsproduceasquarewavevideosignalatm
timesthehorizontalfrequencytoprovidemverticalblackand
whitebars.
Aftereverymcycles,thehorizontalblankingpulsetriggers
themultivibratorsforsynchronizingthebarsignalonevery
line.
AcontrolonthefrontpaneloftheVideoPatternGenerator
enablesvariationofmultivibratorsfrequencytochangethe
numberofbars.

65. Contd…
Similarly,squarewavepulsesderivedeitherfrom50Hz
mainsoffromthemasteroscillatorareusedtotriggeranother
setofmultivibratortogeneratesquarewavevideosignalsthat
arentimestheverticalfrequency.Onfeedingthevideo
amplifiertheseproducehorizontalblackandwhitebars.
Thenumberofhorizontalbarscanalsobevariedby
apotentiometerthatcontrolstheswitchingrateofthe
correspondingmultivibrator.

66. Contd…
Theprovisionofswitchesinthesignalpathofthetwo
multivibratorsenablesthegenerationofvariouspatterns.
IfbothmHandnVswitchesareoff,ablankwhiterasteris
produced.
WithonlythemHswitchon,verticalbarsareproduced,and
withonlythenVswitchon,horizontalbarsaregenerated.
Withbothswitcheson,across-hatchpatternwillbeproduced

67. Contd…
Thehorizontalbarpatternisusedforcheckingvertical
linearity.Thesebarsshouldbeequallyspacedthroughoutthe
screenforlinearity.
Similarly,theverticalbarpatterncanbeusedforcheckingand
settinghorizontallinearity.
Withthecross-hatchpatternformedbytheverticaland
horizontallines,linearitycanbeadjustedmoreprecisely,
becauseanyunequalspacingofthelinescanbediscerned.

68. Contd…
Picturecenteringandaspectratiocanalsobecheckedwiththe
cross-hatchpatternbycountingthenumberofsquaresonthe
verticalandhorizontalsidesofthescreen.
Modulated picture signals are available on limited channels
for injecting into the RF section of the receiver.
Similarly, an FM sound signal with acarrier frequencyof 5.5
MHz ±100 kHz, modulated by a 1 kHz tone, is provided for
aligning sound IF and discriminator circuits.

69. Wave Analyzers
Waveanalyzersevaluatethequalityofthewaveform
generated,distortionandstabilityoftheoutput.
WaveAnalyzerisaninstrumentdesignedtomeasurerelative
amplitudeofsinglefrequencycomponentsinacomplex
waveformordistortedwaveform.
Thecircuitistunedtoaparticularfrequencyandallother
componentsarerejectedanditsamplitudecanbedetermined.

70. Block Diagram of a Basic Wave Analyzer
Abasicwaveanalyzerconsistsofaprimarydetector,whichisa
simpleLCcircuit.
ThisLCcircuitisadjustedforresonanceatthefrequencyofthe
particularharmoniccomponenttobemeasured.
Theintermediatestageisafullwaverectifier,toobtainthe
averagevalueoftheinputsignal.
Theindicatingdeviceisasimpledcvoltmeterthatiscalibrated
toreadthepeakvalueofthesinusoidalinputvoltage.

71. Contd…

72. Contd…
SincetheLCcircuitistunedtoasinglefrequency,itpasses
onlythefrequencytowhichitistunedandrejectsallother
frequencies.
Anumberoftunedfilters,connectedtotheindicatingdevice
throughaselectorswitch,wouldberequiredforausefulWave
analyzer.

73. Contd…
Therearetwotypesofwaveanalyzers:
a)FrequencySelectiveWaveAnalyzer
b)HeterodyneWaveAnalyzer
ApplicationsofWaveAnalyzers:
a)ElectricalMeasurements
b)SoundMeasurements
c)VibrationMeasurements

74. Frequency Selective Wave Analyzer
(AF Wave Analyzer)
Thewaveanalyzer,usedforanalyzingthesignalsofAFrange
iscalledfrequencyselectivewaveanalyzer.
Thisanalyzerconsistsofaverynarrowpassbandfilter
sectionwhichcanbetunedtoaparticularfrequencywithin
AFrange(20Hz–20KHz).

75. Contd…

76. Contd…
Thecomplexwavetobeanalyzedispassedthroughan
adjustableattenuatorwhichservesasarangemultiplierand
permitsalargerangeofsignalamplitudestobeanalyzed
withoutloadingtheamplifier.
Theoutputoftheattenuatoristhenfedtoaselective
amplifier,whichamplifiestheselectedfrequency.

77. Contd…
Thedriveramplifierappliestheattenuatedinputsignaltoa
high-Qactivefilter.
Thishigh-Qfilterisalowpassfilterwhichallowsthe
frequencywhichisselectedtopassandrejectallothers.
Themagnitudeofthisselectedfrequencyisindicatedbythe
meterandthefiltersectionidentifiesthefrequencyofthe
component.

78. Contd…
ThefiltercircuitconsistsofacascadedRCresonant
circuitandamplifiers.
Forselectingthefrequencyrange,thecapacitorsgenerally
usedareoftheclosedtolerancepolystyrenetypeandthe
resistancesusedareprecisionpotentiometers.

79. Contd…
Thecapacitorsareusedforrangechangingandthe
potentiometerisusedtochangethefrequencywithinthe
selectedpass-band,Hencethiswaveanalyzerisalsocalleda
Frequencyselectivevoltmeter.
TheentireAFrangeiscoveredindecadestepsbyswitching
capacitorsintheRCsection.

80. Contd…
Theselectedsignaloutputfromthefinalamplifierstageis
appliedtothemetercircuitandtoanuntunedbufferamplifier.
Themainfunctionofthebufferamplifieristodriveoutput
devices,suchasrecordersorelectronicscounters.
Themeterhasseveralvoltagerangesaswellasdecibelscales
markedonit.Itisdrivenbyanaveragereadingrectifiertype
detector.

81. Contd…
Thewaveanalyzermusthaveextremelylowinputdistortion,
undetectablebytheanalyzeritself.
Thebandwidthoftheinstrumentisverynarrow,typically
about1%oftheselectiveband.

82. Heterodyne Wave Analyzer
Waveanalyzersareusefulformeasurementintheaudio
frequencyrangeonly.
FormeasurementsintheRFrangeandabove(MHzrange),an
ordinarywaveanalyzercannotbeused.
Hence,specialtypesofwaveanalyzersworkingonthe
principleofheterodyning(mixing)areused.
ThesewaveanalyzersareknownasHeterodyneWave
Analyzer.

83. Contd…
Inthiswaveanalyzer,theinputsignaltobeanalyzedis
heterodynedwiththesignalfromtheinternaltunablelocal
oscillatorinthemixerstagetoproduceahigherIFfrequency.
Bytuningthelocaloscillatorfrequency,varioussignal
frequencycomponentscanbeshiftedwithinthepass-bandof
theIFamplifier.TheoutputoftheIFamplifierisrectifiedand
appliedtothemetercircuit.

84. Contd…
Aninstrumentthatinvolvestheprincipleofheterodyningis
theHeterodyningtunedvoltmeter.

85. Contd…
TheinputsignalisheterodynedtotheknownIFbymeansof
atunablelocaloscillator.
Theamplitudeoftheunknowncomponentisindicatedbythe
VTVMoroutputmeter.
TheVTVMiscalibratedbymeansofsignalsof
knownamplitude.

86. Contd…
Thefrequencyofthecomponentisidentifiedbythelocal
oscillatorfrequency,i.e.thelocaloscillatorfrequencyis
variedsothatallthecomponentscanbeidentified.
Thelocaloscillatorcanalsobecalibratedusinginputsignals
ofknownfrequency.

87. Contd…
Thefixedfrequencyamplifierisamultistageamplifierwhich
canbedesignedconvenientlybecauseofitsfrequency
characteristics.
Thisanalyzerhasgoodfrequencyresolutionandcanmeasure
theentireRFfrequencyrange.
Withtheuseofasuitableattenuator,awiderangeofvoltage
amplitudescanbecovered.

88. Contd…
Theirdisadvantageistheoccurrenceofspuriouscross-
modulationproducts,settingalowerlimittotheamplitude
thatcanbemeasured.
TwotypesofselectiveamplifiersfinduseinHeterodynewave
analyzers.
Thefirsttypeemploysacrystalfilter,typicallyhavinga
centrefrequencyof50kHz.

89. Contd…
Byemployingtwocrystalsinaband-passarrangement,itis
possibletoobtainarelativelyflatpass-bandovera4cycle
range.
AnothertypeusesaresonantcircuitinwhichtheeffectiveQ
hasbeenmadehighandiscontrolledbynegativefeedback.
Theresultantsignalispassedthroughahighlyselective3-
sectionquartzcrystalfilteranditsamplitudemeasuredona
Q-meter.

90. Contd…
AmodifiedheterodynewaveanalyzerisshowninFig.9.4.

91. Contd…
Inthisanalyzer,theattenuatorprovidestherequiredinput
signalforheterodyninginthefirstmixerstage,withthe
signalfromalocaloscillatorhavingafrequencyof30—
48MHz.
Thefirstmixerstageproducesanoutputwhichisthe
differenceofthelocaloscillatorfrequencyandtheinput
signal,toproduceanIFsignalof30MHz.

92. Contd…
ThisIFfrequencyisuniformlyamplifiedbytheIFamplifier.
ThisamplifiedIFsignalisfedtothesecondmixerstage,
whereitisagainheterodynedtoproduceadifference
frequencyorIFofzerofrequency.
Theselectedcomponentisthenpassedtothemeteramplifier
anddetectorcircuitthroughanactivefilterwithacutoff
frequencyof1500Hz.

93. Contd…
Themeterdetectoroutputcanthenbereadoffonadb-
calibratedscale,ormaybeappliedtoasecondarydevicesuch
asarecorder.
ThiswaveanalyzerisoperatedintheRFrangeof10kHz—
18MHz,with18overlappingbandsselectedbythefrequency
rangecontrolofthelocaloscillator.
Thebandwidth,whichiscontrolledbytheactivefilter,canbe
selectedat200Hz,1kHzand3kHz.

94. Harmonic Distortion Analyzer
AHarmonicDistortionAnalyzermeasuresthetotalharmonic
powerpresentinthetestwaveratherthanthedistortion
causedbyeachcomponent.
Thesimplestmethodistosuppressthefundamentalfrequency
bymeansofahighpassfilterwhosecutofffrequencyisa
littleabovethefundamentalfrequency.

95. Contd…
Thishighpassallowsonlytheharmonicstopassandthetotal
harmonicdistortioncanthenbemeasured.
OthertypesofHarmonicDistortionAnalyzerbasedon
fundamentalsuppressionareasfollows.
a)EmployingaResonanceBridge
b)Wien’sBridgeMethod
c)BridgedT-NetworkMethod

96. Employing a Resonance Bridge
Thebridgeshownisbalancedforthefundamentalfrequency,
i.e.LandCaretunedtothefundamentalfrequency.

97. Contd…
Thebridgeisunbalancedfortheharmonics,i.e.only
harmonicpowerwillbeavailableattheoutputterminaland
canbemeasured.
Ifthefundamentalfrequencyischanged,thebridgemustbe
balancedagain.
IfLandCarefixedcomponents,thenthismethodissuitable
onlywhenthetestwavehasafixedfrequency.

98. Contd…
IndicatorscanbethermocouplesorsquarelawVTVMs.
Thisindicatesthermsvalueofallharmonics.
Whenacontinuousadjustmentofthefundamentalfrequency
isdesired,aWienbridgearrangementisused.

99. Wien’s Bridge Method
Thebridgeisbalancedforthefundamentalfrequency.
Thefundamentalenergyisdissipatedinthebridgecircuit
elements.
Onlytheharmoniccomponentsreachtheoutputterminals.
Theharmonicdistortionoutputcanthenbemeasuredwith
ameter.
Forbalanceatthefundamentalfrequency,C1,C2,C,
R1=R2=R,R3=2R4.

100. Contd…

101. Bridged T-Network Method
LandC’saretunedtothefundamentalfrequency,andRis
adjustedtobypassfundamentalfrequency.
Thetankcircuitbeingtunedtothefundamentalfrequency,the
fundamentalenergywillcirculateinthetankandis
bypassedbytheresistance.
Onlyharmoniccomponentswillreachtheoutputterminals
andthedistortedoutputcanbemeasuredbythemeter.

102. Contd…
TheQoftheresonantcircuitmustbeatleast3-5.

103. Contd…
OnewayofusingabridgeT-networkisgiveninFig.9.8.

104. Contd…
TheswitchSisfirstconnectedtopointAsothat
theattenuatorisexcludedandthebridgeT-networkisadjusted
forfullsuppressionofthefundamentalfrequency,i.e.
minimumoutput.
MinimumoutputindicatesthatthebridgedT-networkistuned
tothefundamentalfrequencyandthatthefundamental
frequencyisfullysuppressed.

105. Contd…
TheswitchisnextconnectedtoterminalB,i.e.thebridgedT-
networkisexcluded.
Attenuationisadjusteduntilthesamereadingisobtainedon
themeter.
Theattenuatorreadingindicatesthetotalrmsdistortion.

106. Contd…
Distortionmeasurementcanalsobeobtainedbymeansof
awaveanalyzer,knowingtheamplitudeandthefrequencyof
eachcomponent,theHarmonicDistortionAnalyzercanbe
calculated.
However,distortionmetersbasedonfundamentalsuppression
aresimplertodesignandlessexpensivethanwaveanalyzers.
Thedisadvantageisthattheygiveonlythetotaldistortion
andnottheamplitudeofindividualdistortioncomponents.

107. Capacitance –Voltage Analyzers
Thecapacitancevoltageanalyzersarespeciallyusedto
measureandanalyzethecapacitanceversusvoltage(CV)and
capacitanceversustime(CT)characteristicsofspecial
semiconductordevicessuchasPNjunctiondiodes,schottky
diodes,metalinsulatedsemiconductors(MIS),FET’setc.,
Thecharacteristicsofsuchdevicescanbetestedusingahigh
frequencysignaloftypically100KHz.or1MHz.

108. Contd…
Insemiconductordevices,dopingprofiles,oxide
characteristics,densityofmobileions,lifetimeofminority
chargecarriers,thresholdvoltageetc.,areveryimportant
characteristics.
ByusingCVAnalyzerormeter,theCVandCT
characteristicscanbeusedtodeterminetheabovementioned
characteristics.

109. Features of CV analyzers
Sensitivetosmalltestdevices
Smallsignalvoltages
Internalsupplyprovides50mAfrom-20Vto+20Vwith
resolutionupto5mV.
At100KHz.,largeleakyorforwardbiaseddevicesupto
20mFcanbetested.
Readingsupto1000/sec.
SupplyvoltageisDc,staircaseorpulse.

110. Spectrum Analyzer
Themostcommonwayofobservingsignalsistodisplaythem
onanoscilloscope,withtimeastheX-axis(i.e.amplitudeof
thesignalversustime).Thisisthetimedomain.
Itisalsousefultodisplaysignalsinthefrequencydomain.
Theinstrumentprovidingthisfrequencydomainviewisthe
spectrumanalyzer.

111. Contd…
ASpectrumAnalyzerBlockDiagramprovidesacalibrated
graphicaldisplayonitsCRT,withfrequencyonthehorizontal
axisandamplitude(voltage)ontheverticalaxis.
Displayedasverticallinesagainstthesecoordinatesare
sinusoidalcomponentsofwhichtheinputsignaliscomposed.
Theheightrepresentstheabsolutemagnitude,andthe
horizontallocationrepresentsthefrequency.

112. Contd…
Theseinstrumentsprovideadisplayofthefrequency
spectrumoveragivenfrequencyband.
Spectrumanalyzersuseeitheraparallelfilterbankoraswept
frequencytechnique.
Inaparallelfilterbankanalyzer,thefrequencyrangeis
coveredbyaseriesoffilterswhosecentralfrequenciesand
bandwidtharesoselectedthattheyoverlapeachother,as
showninFig.9.9(a).

113. Contd…
Typically,anaudioanalyzerwillhave32ofthesefilters,each
coveringonethirdofanoctave.
Forwidebandnarrowresolutionanalysis,particularlyatRF
ormicrowavesignals,theswepttechniqueispreferred.

114. Contd…

115. Basic Spectrum AnalyzerUsing Swept Receiver Design
Referringtotheblockdiagram,thesawtoothgenerator
providesthesawtoothvoltagewhichdrivesthehorizontalaxis
elementofthescopeandthissawtoothvoltageisfrequency
controlledelementofthevoltagetunedoscillator.
Astheoscillatorsweepsfromf
mintof
maxofitsfrequencyband
atalinearrecurringrate,itbeatswiththefrequency
componentoftheinputsignalandproduceanIF,whenevera
frequencycomponentismetduringitssweep.

116. Contd…
Thefrequencycomponentandvoltagetunedoscillator
frequencybeatstogethertoproduceadifferencefrequency,
i.e.IF.
TheIFcorrespondingtothecomponentisamplifiedand
detectedifnecessary,andthenappliedtotheverticalplatesof
theCRO,producingadisplayofamplitudeversusfrequency.


117. Contd…

118. Contd…
Thespectrumproducediftheinputwaveisasingletoned
A.M.isgiveninFigs9.10,9.11,and9.12.

119. Contd…

120. RF Spectrum Analyzer
The frequency range covered by this instrument is from 1
MHz to 40 GHz. The basic block diagram (Fig. 9.13) is of a
spectrum analyzer covering the range 500 kHz to 1 GHz,
which is representative of a super heterodyne type.
The input signal is fed into a mixer which is driven by a local
oscillator. This oscillator is linearly tunable electrically over
the range 2 —3 GHz.

121. Contd…
The mixer provides two signals at its output that are
proportional in amplitude to the input signal but of
frequencies which are the sum and difference of the
input signal and local oscillator frequency.

122. Contd…
TheIFamplifieristunedtoanarrowbandaround2
GHz,sincethelocaloscillatoristunedovertherange
of2—3GHz,onlyinputsthatareseparatedfrom
thelocaloscillatorfrequencyby2GHzwillbe
convertedtoIFfrequencyband,passthroughthe
IFfrequencyamplifier,getrectifiedandproducea
verticaldeflectionon the CRT.

123. Contd…
Fromthis,itisobservedthatasthesawtoothsignal
sweeps,thelocaloscillatoralsosweepslinearlyfrom
2—3GHz.Thetuningofthespectrumanalyzerisa
sweptreceiver,whichsweepslinearlyfrom0to1
GHz.

124. Contd…
Thesawtoothscanningsignalisalsoappliedtothe
horizontalplatesoftheCRTtoformthefrequency
axis.(TheSpectrumAnalyzerBlockDiagramisalso
sensitivetosignalsfrom4—5GHzreferredtoas
theimagefrequencyofthesuperheterodyne.

125. Contd…
Alowpassfilterwithacutofffrequencyabove1
GHzattheinputsuppressesthesespurioussignals.)
Spectrumanalyzersarewidelyusedinradars,
oceanography,and bio-medicalfields.

126. Power Analyzers
In modern Industrial applications, number of
electronic appliances connected to ac line.
Due to this, it is observed that the input connected to
every device may not be a clean steady sinusoidal
waveform with constant amplitude.
Hence, when any device does not work properly, it is
necessary to check the quality of input power.

127. Contd…
So, if the power line and the appliances are perfect,
no power problem would be observed.
But practically, load connected to ac line and power
distribution both contribute to power problem.
Power analyzers evaluate power problem and also
provides complete documentation of tests performed.

128. Contd…
The block diagram of a power analyzer is shown for
a 3-phase, 4 wire system of supply.

129. Contd…
The current in each line and line voltages are sensed
using dedicated sensors.
The line voltages are sensed by using sensors Vry,
Vyband Vbr.
The current in each line are sensed by using Cr, Cy
and Cb.
These sensed currents and voltages are selected
sequentially by using multiplexer.

130. Contd…
The multiplexer combines all the above signals into a
single channel.
The output of the multiplexer is connected to ADC.
The analog signal gets converted to digital signal
which is given to the micro controller.
According to the program stored in memory of micro
controller, computation and calculations are done.

131. Contd…
Finally, the calculated the quantities are displayed
using the display unit.
Parameters measured by the Power Analyzer
The power analyzer measures all the line currents
and line voltages at set sampling rate.
It can also calculate power and related quantities and
can carry out harmonic analysis of voltages and
currents.

132. Contd…
Power Supply used
Supply frequency of 50 Hz. Or 60 Hz.
3 –phase, 4 wire system power supply.
In some cases, 3 –phase, 3 wire system is also used.

133. Contd…
Applications
Product Development
Troubleshooting areas of Power distribution
To monitor power and operation of the device
malfunctioning
To indicate problem cause using a recorded event