experiment 6

7/21/2019 Experiment 6

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Electrical Circuits I Laboratory (ENRE 2110)

Deanship of Engineering Fall 2007

German Jordanian University Laboratory Experiment (! """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Function Generators and the Oscilloscope

- Objectives:

#$ %o introd&'e the &se of f&n'tion generators for signal generation$2$ %o introd&'e the &se of s'illos'opes for signal meas&rements$

- Introduction and !eory:

) "unction #enerator is a pie'e of ele'troni' test e*&ipment &sed to generateele'tri'al +aveforms$ %hese +aveforms 'an be either repetitive or single,shot (on'e only!

in +hi'h 'ase some -ind of triggering so&r'e is re*&ired (internal or external!$ %he

res&ltant +aveforms 'an be applied to a devi'e &nder test and analy.ed as they progressthro&gh the devi'e/ 'onfirming the proper operation of the devi'e or pinpointing a fa&lt in

it$

)nalog f&n'tion generators &s&ally generate a triangle +aveform as the basis for

all of its other o&tp&ts$ %he triangle is generated by repeatedly 'harging and dis'harging a'apa'itor from a 'onstant '&rrent so&r'e$ %his prod&'es a linearly as'ending or

des'ending voltage ramp$ )s the o&tp&t voltage rea'hes &pper and lo+er limits/ the

'harging and dis'harging is reversed &sing a 'omparator/ prod&'ing the linear triangle+ave$ y varying the '&rrent and the si.e of the 'apa'itor/ different fre*&en'ies may be

obtained$

$i#ure 1% 1aveforms at the o&tp&t of af&n'tion generator$

) 03 d&ty 'y'le s*&are +ave is easily obtained by noting +hether the 'apa'itoris being 'harged or dis'harged/ +hi'h is refle'ted in the '&rrent s+it'hing 'omparator4s

o&tp&t$ 5ost f&n'tion generators also 'ontain a non,linear diode shaping 'ir'&it that 'an



1aveform shapes reveal a great deal abo&t a signal$ )ny time yo& see a 'hange in

the height of the +aveform/ yo& -no+ the voltage has 'hanged$ )ny time there is a flathori.ontal line/ yo& -no+ that there is no 'hange for that length of time$ :traight/

diagonal lines mean a linear 'hange = rise or fall of voltage at a steady rate$ :harp angles

on a +aveform indi'ate s&dden 'hange$ Fig&re sho+s some 'ommon +aveforms$

$i#ure '$ :ome 9ommon 1aveforms$

:ignals s&'h as steps and p&lses that o''&r rarely/ or non,periodi'ally/ are 'alled

single,shot or transient signals$ ) step indi'ates a s&dden 'hange in voltage/ similar to thevoltage 'hange yo& +o&ld see if yo& t&rned on a po+er s+it'h$ ) p&lse indi'ates s&dden

'hanges in voltage/ similar to the voltage 'hanges yo& +o&ld see if yo& t&rned a po+er

s+it'h on and then off again$ ) p&lse might represent one bit of information traveling



thro&gh a 'omp&ter 'ir'&it or it might be a glit'h/ or defe't/ in a 'ir'&it$ ) 'olle'tion of

p&lses traveling together 'reates a p&lse train$ Digital 'omponents in a 'omp&ter

'omm&ni'ate +ith ea'h other &sing p&lses$ &lses are also 'ommon in x,ray and'omm&ni'ations e*&ipment$ Fig&re sho+s examples of step and p&lse shapes and a

p&lse train$

$i#ure % Different p&lse shapes$

;epetitive signals are referred to as periodi' signals/ +hile signals that 'onstantly

'hange are -no+n as non,periodi' signals$ ) still pi't&re is analogo&s to a periodi' signal/+hile a moving pi't&re 'an be e*&ated to a non,periodi' signal$

1hen a timing relationship exists bet+een t+o signals/ those signals are referred

to as syn'hrono&s$ 9lo'-/ data and address signals inside a 'omp&ter are an example of

syn'hrono&s signals$ )syn'hrono&s is a term &sed to des'ribe those signals bet+een+hi'h no timing relationship exists$ e'a&se no time 'orrelation exists bet+een the a't of

to&'hing a -ey on a 'omp&ter -eyboard and the 'lo'- inside the 'omp&ter/ these are

'onsidered asyn'hrono&s$

:ome +aveforms 'ombine the 'hara'teristi's of sines/ s*&ares/ steps/ and p&lses

to prod&'e +ave shapes that 'hallenge many os'illos'opes$ %he signal information may be embedded in the form of amplit&de/ phase/ andor fre*&en'y variations$ For example/altho&gh the signal in Fig&re is an ordinary 'omposite video signal/ it is 'omposed of

many 'y'les of higher,fre*&en'y +aveforms embedded in a lo+er,fre*&en'y envelope$ 6n

this example/ it is &s&ally most important to &nderstand the relative levels and timingrelationships of the steps$ %o vie+ this signal/ yo& need an os'illos'ope that 'apt&res the

lo+,fre*&en'y envelope and blends in the higher,fre*&en'y +aves in an intensity,graded

fashion so that yo& 'an see their overall 'ombination as an image that 'an be vis&allyinterpreted$ )nalog and digital phosphor os'illos'opes are most s&ited to vie+ing

'omplex +aves/ s&'h as video signals/ ill&strated in Fig&re $ %heir displays provide the

ne'essary fre*&en'y,of,o''&rren'e information/ or intensity grading/ that is essential to

&nderstanding +hat the +aveform is really doing$



$i#ure % ) 9omplex signal$

$re*uency and +eriod6f a signal repeats/ it has a fre*&en'y$ %he fre*&en'y is meas&red in ert. (.!

and e*&als the n&mber of times the signal repeats itself in one se'ond/ referred to as'y'les per se'ond$ ) repetitive signal also has a period , t!is is t!e aount o" tie it

ta.es t!e si#nal to co&lete one cycle% eriod and fre*&en'y are re'ipro'als of ea'h

other/ so t!at 1/&eriod e*uals t!e "re*uency and #fre*&en'y e*&als the period$ Forexample/ the sine +ave in Fig&re #0 has a fre*&en'y of . and a period of # se'ond$

olta#eHoltage is the amo&nt of ele'tri' potential = or signal strength = bet+een t+o

points in a 'ir'&it$ Us&ally/ one of these points is gro&nd/ or .ero volts/ b&t not al+ays$

?o& may +ant to meas&re the voltage from the maxim&m pea- to the minim&m pea- of a

+aveform/ referred to as the pea-,to,pea- voltage$

&litude)mplit&de refers to the aount o" volta#e beteen to &oints in a 'ir'&it$

)mplit&de 'ommonly refers to the a3iu volta#e o" a si#nal easured "ro

#round4 or .ero volts$ %he +aveform sho+n in Fig&re ## has an

amplit&de of # H and a pea-,to,pea- voltage of 2 H$

$i#ure 5% Fre*&en'y and amplit&de meas&rements$

+!asehase is best explained by loo-ing at a sine +ave$ %he voltage level of sine +aves

is based on 'ir'&lar motion$ Given that a 'ir'le has 0I/ one 'y'le of a sine +ave has0I/ as sho+n in Fig&re ##$ Using degrees/ yo& 'an refer to the phase angle of a sine

+ave +hen yo& +ant to des'ribe ho+ m&'h of the period has elapsed$ +!ase s!i"t

describes t!e di""erence in tiin# beteen to ot!erise siilar si#nals $ %he+aveform in Fig&re #2 labeled B'&rrentC is said to be 0I o&t of phase +ith the +aveform

labeled Bvoltage/C sin'e the +aves rea'h similar points in their 'y'les exa'tly # of a

'y'le apart (0I K 0I!$ hase shifts are 'ommon in ele'troni's$



$i#ure 6% hase meas&rements$

!e y&es o" Oscillosco&esEle'troni' e*&ipment 'an be 'lassified into t+o 'ategories> analo# and di#ital%

nalo# e*ui&ent or.s it! continuously variable volta#es4 !ile di#ital

e*ui&ent or.s it! discrete binary nubers t!at re&resent volta#e sa&les$ )

'onventional phonograph is an analog devi'e/ +hile a 'ompa't dis' player is a digital

devi'e$ s'illos'opes 'an be 'lassified similarly = as analog and digital types$ For manyappli'ations/ either an analog or digital os'illos'ope +ill do$ o+ever/ ea'h type has

&ni*&e 'hara'teristi's that may ma-e it more or less s&itable for spe'ifi' appli'ations$Digital os'illos'opes 'an be f&rther 'lassified into digital storage os'illos'opes (D:s!/

digital phosphor os'illos'opes (Ds! and sampling os'illos'opes$

nalo# Oscillosco&es

F&ndamentally/ an analog os'illos'ope +or-s by applying the meas&red signal

voltage dire'tly to the verti'al axis of an ele'tron beam that moves from left to right

a'ross the os'illos'ope s'reen = &s&ally a 'athode,ray t&be (9;%!$ %he ba'- side of thes'reen is treated +ith l&mino&s phosphor that glo+s +herever the ele'tron beam hits it$

%he signal voltage defle'ts the beam &p and do+n proportionally as it moves hori.ontally

a'ross the display/ tra'ing the +aveform on the s'reen$ %he more fre*&ently the beam hitsa parti'&lar s'reen lo'ation/ the more brightly it glo+s$

%he 9;% limits the range of fre*&en'ies that 'an be displayed by an analog

os'illos'ope$ )t very lo+ fre*&en'ies/ the signal appears as a bright/ slo+,moving dotthat is diffi'&lt to disting&ish as a +aveform$ )t high fre*&en'ies/ the 9;%s +riting

speed defines the limit$ 1hen the signal fre*&en'y ex'eeds the 9;%s +riting speed/ the



display be'omes too dim to see$ %he fastest analog os'illos'opes 'an display fre*&en'ies

&p to abo&t # G.$

1hen yo& 'onne't an os'illos'ope probe to a 'ir'&it/ the voltage signal travelsthro&gh the probe to the verti'al system of the os'illos'ope$ Fig&re M ill&strates ho+ an

analog os'illos'ope displays a meas&red signal$ Depending on ho+ yo& set the verti'al

s'ale (voltsdiv 'ontrol!/ an atten&ator red&'es the signal voltage and an amplifierin'reases the signal voltage$ 8ext/ the signal travels dire'tly to the verti'al defle'tion

plates of the 9;%$ Holtage applied to these defle'tion plates 'a&ses a glo+ing dot to

move a'ross the s'reen$ !e #loin# dot is created by an electron bea t!at !its t!e

luinous &!os&!or inside t!e CR$ ) positive voltage 'a&ses the dot to move &p +hile

a negative voltage 'a&ses the dot to move do+n$

$i#ure 7% )nalog s'illos'ope$

%he signal also travels to the trigger system to start/ or trigger/ a hori.ontal s+eep$

ori.ontal s+eep refers to the a'tion of the hori.ontal system that 'a&ses the glo+ing dotto move a'ross the s'reen$ %riggering the hori.ontal system 'a&ses the hori.ontal time

base to move the glo+ing dot a'ross the s'reen from left to right +ithin a spe'ifi' time

interval$ 5any s+eeps in rapid se*&en'e 'a&se the movement of the glo+ing dot to blend

into a solid line$ )t higher speeds/ the dot may s+eep a'ross the s'reen &p to 00/000times per se'ond$ %ogether/ the hori.ontal s+eeping a'tion and the verti'al defle'tion

a'tion tra'e a graph of the signal on the s'reen$ %he trigger is ne'essary to stabili.e arepeating signal = it ens&res that the s+eep begins at the same point of a repeating signal/res&lting in a 'lear pi't&re as sho+n in Fig&re $

6n addition/ analog os'illos'opes have fo'&s and intensity 'ontrols that 'an beadN&sted to 'reate a sharp/ legible display$ eople often prefer analog os'illos'opes +hen

it is important to display rapidly varying signals in Breal timeC = or/ as they o''&r$ %he

analog os'illos'opes 'hemi'al phosphor,based display has a 'hara'teristi' -no+n as



intensity grading that ma-es the tra'e brighter +herever the signal feat&res o''&r most

often$ %his intensity grading ma-es it easy to disting&ish signal details N&st by loo-ing at

the tra'es intensity levels$

$i#ure 8% %he trigger stabili.es a repetitive +aveform/ 'reating a 'lear pi't&re$

9i#ital Oscillosco&es

6n 'ontrast to an analog os'illos'ope/ a digital os'illos'ope &ses an analog,to,digital 'onverter ()D9! to 'onvert the meas&red voltage into digital information$ 6t

a'*&ires the +aveform as a series of samples/ and stores these samples &ntil it

a''&m&lates eno&gh samples to des'ribe a +aveform$ %he digital os'illos'ope then re,

assembles the +aveform for display on the s'reen$ (see Fig&re #0! Digital os'illos'opes

'an be 'lassified into digital storage os'illos'opes (D:s!/ digital phosphor os'illos'opes(Ds!/ and sampling os'illos'opes$ %he digital approa'h means that the os'illos'ope

'an display any fre*&en'y +ithin its range +ith stability/ brightness/ and 'larity$ Forrepetitive signals/ the band+idth of the digital os'illos'ope is a f&n'tion of the analog

band+idth of the front,end 'omponents of the os'illos'ope/ 'ommonly referred to as the

=d point$ For single,shot and transient events/ s&'h as p&lses and steps/ the band+idth'an be limited by the os'illos'opes sample rate$



$i#ure 10% )nalog os'illos'opes tra'es signals/ +hile digital os'illos'opes samples the

signals and 'onstr&'ts displays$

1hile a D: &ses a serial,pro'essing ar'hite't&re to 'apt&re/ display and analy.e

signals/ a D employs a parallel,pro'essing ar'hite't&re to perform these f&n'tions$ %heD ar'hite't&re dedi'ates &ni*&e ):69 hard+are to a'*&ire +aveform images/

delivering high +aveform 'apt&re rates that res&lt in a higher level of signal vis&ali.ation$

%his performan'e in'reases the probability of +itnessing transient events that o''&r in

digital systems/ s&'h as r&nt p&lses/ glit'hes and transition errors$

9i#ital a&lin# Oscillosco&es1hen meas&ring high,fre*&en'y signals/ the os'illos'ope may not be able to

'olle't eno&gh samples in one s+eep$ ) digital sampling os'illos'ope is an ideal tool for

a''&rately 'apt&ring signals +hose fre*&en'y 'omponents are m&'h higher than the

os'illos'opes sample rate$ %his os'illos'ope is 'apable of meas&ring signals of &p to anorder of magnit&de faster than any other os'illos'ope$ 6t 'an

a'hieve band+idth and high,speed timing ten times higher than other os'illos'opes for

repetitive signals$ :e*&ential e*&ivalent,time sampling os'illos'opes are available +ith band+idths to 0 G.$

%he tradeoff for this high band+idth/ ho+ever/ is that the sampling os'illos'opes

dynami' range is limited$ %herefore/ the dynami' range of most sampling os'illos'opes islimited to abo&t # H pea-,to,pea-$ Digital storage and digital phosphor os'illos'opes/ on

the other hand/ 'an handle 0 to #00 volts$



6n the lab/ the D:,##0 Digital s'illos'ope +ill be &sed$ %he front panel of the

os'illos'ope loo-s li-e Fig&re ##$

Vertical Control Horizontal Control Trigger Control Menus

Menu Boxes Menu Selections

$i#ure 11% D:,##0 s'illos'ope from EA Ele'troni's/ Oorea$

)$ Herti'al 9ontrol>1. HoltsDiv (9#/ 92!> Adjusts the vertical scale factor of the scope

waveform.

2. 9#92 5en&> Shows the channel function and channel waveform

display On/Off.

3. 5ath 5en&> Shows the ath functions than can !e applied to the currentwaveforms.

". 9#92 osition> Adjusts the vertical position of the scope waveform.



$ bserve the +aveform yo& see on the s'ope$ 9hange the HoltsDiv to in'rease

its amplit&de on the s'reen by 'hanging the fa'tor on the y,axis/ also/ 'hange the

%imeDiv to expand it on the x,axis for better vie+$ 8o+/ 'o&nt the n&mber ofdivisions on the y,axis and m&ltiply it +ith the fa'tor for 9# to get the ea-,to

ea- voltage of the +aveform$ ;e'ord this val&e$ 1hat is the amplit&de of the

signalR 1rite it do+n$ )lso/ 'o&nt the n&mber of divisions on the x,axis for a f&ll'y'le/ and m&ltiply +ith the time fa'tor sho+n on the s'ope s'reen$ 1hat does

this representR 9al'&late the fre*&en'y of the signal$ Did it mat'h the 1 >?@ yo&

s&ppliedR

$ 9onne't the 'ir'&it sho+n in the fig&re$ 9onne't the passive probe to 9#/ and'onne't its other tip to the 'ir'&it$ 9onne't the G8D of the probe to the lo'ation

sho+n$ bserve and re'ord the amplit&de (pea- voltage!/ as +ell as the fre*&en'y

of the voltage a'ross the 2 O Ω resistor$

$ ress the 9# men&$ 6n the se'ond

men& box +here is says cou&lin#/ 'hoose9C$ ;e'ord the graph on yo&r note boo-

(ma-e s&re to get the amplit&des andfre*&en'ies in yo&r plots!$

7$ 8o+/ 'hange the 'o&pling of 9# to C

'o&pling$ 1hat is the differen'e

bet+een 9C and C 'o&plingR1hat happened to the +aveformR

M$ Dis'onne't the s'ope probe from the 'ir'&it$

;e'onne't the o&tp&t from the F$G$ to the s'opedire'tly$ 5a-e s&re that yo& still have 5< in the)mplit&de S3T$ 8o+/ s+it'h to a rectan#ular ave$ ;e'ord the +aveform yo&

see (:-et'h it!$ 6n'rease the 3 amplit&de to 8< then 12<$ 1hat happens to the

amplit&de of the signalR ;e'ord the val&es yo& obtain$

$ ress the Aat! b&tton$ 6n the rit!etic +indo+/ 'hoose IN C?1$ 1hathappens to yo&r s*&are +aveR %&rn the rit!etic f&n'tion o"" / +hat happens

no+R

#0$ 9hange the F$G$ o&tp&t to be a trian#ular +aveform$ :et the amplit&de to

12</ and re'ord the amplit&de and fre*&en'y of the signal 'oming o&t of the F$G$and then s-et'h it$

##$ From the nstruments/ volta%e sources men& 'hoose pulse %enerator $ :et the

amplit&de to 12</ and fre*&en'y to 10>?@$ :et the &ulse idt! +B;<= to be

10<$ 5eas&re the +aveform and s-et'h it$ %hen/ 'hange the +B ;<= to 60<$

5eas&re the +aveform and s-et'h it$ 1hat does the d&ty 'y'le doR

Function

Generator

5 V

1.2 K

2 K

CH

G

experiment 6

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