UNESCO-NIGERIA TECHNICAL & VOCATIONAL
EDUCATION REVITALISATION PROJECT-PHASE II
NATIONAL DIPLOMA IN
ELECTRICAL ENGINEERING TECHNOLOGY
ELECTRONICS I I
COURSE CODE: EEC234
YEAR II- SEMESTER III
PRACTICAL
Version 1: December 2008
TABLE OF CONTENTS
Department
Electrical Engineering Technology
Subject
Electronics II
Year
2
Semester
III
Course Code
EEC 234
Credit Hours
4
Theoretical
1
Practical
3
Week 1
FIELD EFFECT TRANSISTOR (FET) STATIC CHARACTERISTIC IN COMMON SOURCE
CONFIGURATTION
Week 2
DISCUSSION ON THE RESULT AND ANALYSIS OF FIELD EFFECT TRANSISTOR (FET) STATIC
CHARACTERISTIC IN COMMON SOURCE CONFIGURATION
Week 3
COMMON EMITTER AMPLIFIER CHARACTERISTIC
Week 4
DISCUSSION ON THE RESULT AND ANALYSIS OF COMMON EMITTER AMPLIFIER
Week 5
COMMON BASE AMPLIFIER
Week 6
DISCUSSION ON THE RESULT AND ANALYSIS OF COMMON BASE AAMPLIFIER
Week 7
COMMON COLLECTOR AMPLIFIER (EMITTER FOLLOWER) CHARACTERISTIC
Week 8
DISCUSSION ON THE RESULT AND ANALYSIS OF THE COMMON COLLECTOR AMPLIFIER
CHARACTERISTIC
Week 9
FRQUENCY RESPONSE CHARACTERISTIC OF A COMMON EMITTER AMPLIFIER
Week 10
DISCUSSION ON THE RESULT OF THE FREQUENCY RESPONSE CHARACTERISTIC OF THE
COMMOM EMITTER AMPLIFIER
Week 11
COMMON EMITTER AMPLIFIER IMPEDANCE,POWER AND PHASE RELATIONSHIP
Week 12
DISCUSSION ON THE RESULT OF THE COMMON EMMITER AMPLIFIER IMPEDANCE, POWER
AND PHASE RELATIONSHIP
Week 13
TRANSFORMER COUPLED CLASS A AMPLIFIER
Week 14
DISCUSSION ON THE RESULT AND ANALYSIS FOR THE TRANSFORMER COUPLED CLASS A
AMPLIFIER
Week 15
TRANSFORMER COUPLED CLASS B AMPLIFIER
1
PZgIQ €PyICy 3QANSIS7OR (Ifl7) SVAYIC CHARAC¥'E¥IS’I¥CS
0 CO’MMO¥ SOOCE CONFIGURATION
tion transistors. In this experiment we shall concern ourselves maialy with the N- channel JFET only.
1.
Toinvestigatethe staticoutput(drain) characteristics
of junction field effect Transistor (JFET) int£e com- In the FET the drsin corresponds to the collector of a bimon-source configuration.
2.
To investigate the transfer characteristics of JFET.
polar transistor, the soatce to the emitter, and the date to the
6ue. The major operational ‹difference is that the drain
current (ID) 8 the JFET is controlled by gate-to-source
voltage(VGS),whereas collector current inthebi-polartransistor is controlled by base current.
Like the bi-polar junction transistor, the FET has three
electrodes, namely: the date (G), soume (S), and drain (D).
FETs are made in various forms. The construction and symbolof the junction FET (JFET) type are show in Fig. 5.1
Fig. 5.2 shows the bias arrangement for an N-channelJFET.
Here, plc notice that the gate G is reverse-biased relative to
the source while the drain is forward-biased relatire to the
SOMCg.
Drain (D)
Channel
Depletion.
region
G (G)
VDD
(a) Construction
Vcs
Fig. 52: The bias armngement for an N-channel JFET.
Tbe channel is a resistive patb through wbicb voltage *as
can drive a current D
Vcs
(b) Symbol
Fig. 5.1: JFET
The fF£T bas two forms namely: N-channel and P-Channel
types, v6icâ we analogous to PNP and NPN bi-polar junc-
If a battery +nD is connected across the channel, Ltd the
polarity shown, the negative - charge carriers (electrons) in
the N channel move toward the positive termini of tâe
battery, and electrons from tfie negative ternind of the
battery move through the source into tfie N channel to
replace those that vacated the drain. In this way, current
the circuit will continue as long as the circuit is complete. In
this way, a limited control of current is possible by varying
V
- D
The drain current Ip is controlled essentially by varying a
reverse-biased voltage Vcs Increase in the negative value of
As shown in Fig. 5.3(a), the pinch-off voltage Vp is the
voltage value at which ID no longer increases with increased
VDs probably until Vos(tax)is reached. Fig, SP(b) show
the family of drain characteristics for different values of Yes.
Vcs has the effect of widening the depletion region in the Each output (drain) characteristic can broadly be tubchannel (see Fig. 5.2 above) and blocking the channel and divided into four regions, as clearly marked in Fig. 5.3(a).
consequently.ID decreases.
These are, namely:
If the gate is connected directly to the source (Vcs = 0). D (i) the resistive region, where YDs Vp (region I)
will rise graduallyto the maximum value of Ipy ast6e drainsowce voltage ( Ds) increases to the pinch-off voltage, Vp. (ii) Onset of pinch-off, where +Ds = Vp. (region II)
ID
VGS = 0V
(iii)
Pinch-off region, where VDs > Vp (region III)
(iv)
break-down region (region IV).
From the drain characteristic curves, it is possible to determine the following parameters of JFET:
(i)
drain (or output) resistance,
(Oluos) for VGS = coast. (fed) (S.1)
Vns
AVns
Vm(ma)
(a)
Output (drain) characteristics of JFET when VGA =
for ID = const. (fixed)
(5.2)
(iii) mutual conductance,
OV.
g- BAGS(Sieaeas)
Note that gp can also be determined directly from the transfer characteristic discussed below.
s”
The transfer characteristic which is a plot of ID versusVGA
for a constant value of Yes› is shown in Fig. 5.4. This curry
D
can be plotted also by using the same experimental circuit of
Fig. 5.5 used for plotting the drain characteristics. In tku
C
2--
SGS - -1.0V
i
A
z vr
(b)
for VDs = const. (fixed) (SJ)
4
6
s
Vcs --2.0V
10
20
case however, VDSi keptat some constant value while Ypt
is varied, and I D » measured. When the resultsare plotted
they will resemble what we have in Fig. 5.4.
Alternatively, we can select a value of VDS (Sity, VDS -
+6V) on the drain characteristics (Fig 5.3(b)) and draw i
line vertically upward to intercept the drain characteristic
curves at points A,B,C,D and E. The next step is then tc
determine the corresponding value of ID and VGS at th
points A,B,C,D and E to plot the transfer curve from th
Pamily of output (drain) characteristics of n-channel
JFET.
family of drain characteristic curves. The corresponding
Flg. $3: Ouput characterlstit currts of JFET
values of *GS and Ip, read from the drain characteristic
DSS and that D 0, when VpJ = Yp as seen on the transfer
characteristic curve of Fig. 5.4.
VDs
+ 6V
References
Boylestad, R and Nashelsky; L. Electronic Devices and Circuit Theory. Prentice - Hall, 4th Edition, New Jersey, 1987,
pp. 388 - 390.
Lurch, E. N. Fundamentals of Electronics, 3rd Edition, John
Wiley, New York, 1981, pp. 213 - 220.
'f
3
v,“
-2
-
0
Linear potentiometers - 500f2, 2.5kf2 and 5kf2 (1 each)
Flg. 5.4: JFET transfer characteristic (n<hannel)
curves serve as the coordinates of points on the ID versus
VGs*urve.
Two important points on the transfer characteristic curve
show in Fig, 5.4. are the values Ipss and Vp. When these
points are fixed, the rest of the curve can be obtained
theoretically from the relation.
Ip = IDSS 1 -
2
vGs
(3.4)
VD
JFET, 2N38l9 or any other suitable n-channel JFET (e.g.
2N5484, or equi dent)
Stabilised (dual) power supply unit 0-30V d.c., FARNELL type LT 30-1 or equivalent.
D.C. milliameters (1 No each) with ranges (0-2)mA; (05)mA; and (0-10)mA.
D.C. voltmeters (lNo each) with ranges
(-10'V-0-(+ 10V); aad (0 - 30)V.
Connection leads.
which represents the transfer characteristic curve of Fig. 5.4.
Notice that from Equation (5.4) when Vcs
0, the ID
VDD = -1- UV
Ri
2N3819
0-30V
(-10 • 0 -10)V
Fig. SP: Circuit for investigatlng JFET characteristics
fl8b/ b/i
'
VGS,V
(i)
Connect the circuit of Fig. 5.5, and set RJ to give and
keep Ycs = 0.
(ii)
Adjust Ri, R3 accordingly in order to set Ans - 0
initially. Next, increase Vps in step of lY, starting
from 0V untd a maximum of 10V is reached and
measure the c0«ispondingID in each case. Record
2.
your readings as slow in Table 5,1.
(i?i) Repeat step (ii) for Pcs
+0SV separately.
{b)
(Y) IJsingths saae circuit ofFig. 5.5, setaad keep Vis at
10V.
t
(fi) Pleasure aad record ia Tablc S.2 the values of ID lo
each value of Vcs
0V, -03V, -1.0V, 1.SV, -2.0V
aad -2.W
7ablc 5.1: MzasurUocats oa éraia cbaractcrlstlcs
G9 -
Q9 -
+0.5V +0.25V
io
CGI"
G9-
VGS ^
/G9^
+0V *0.15V *0.5V *0.7ST
4J
0
Froza your grapftsia step 1, estknate tbe ydye o(Yp,
IDSS*
Obtaiareadings /or/D aad Ycsm ole the drain c6aracteristic curves for Vg = 10V. Use tbese resdts to
plot tire transfer characteristic cure. How does this
plot compare Ntâ the one obtained in step 2?
(c) Froa tote grapb in step 1, deteroiac tb ovtpvt
(6aia) resistaace at tote following poiats:
(i) VDS - 1V, VGS - + 0.IV
(ii) VDS = 8V, Vcs = + 0.25V
Compare your results and comment.
(d)
Froa the grapf› in step 1, detemiae
(i)
(ii)
(e)
the voltage gets of the JFET'f0r D
tbe zautizl coaducttoce o(tbe JFET for
Determine this saac factual conductaacc froza the
g 3 )1 III 5(e
’D
-1.0
Using the results in Table 5.2, plot the transfer câar-
60.W, u Pcs =
milliammeter to measure If to ensure accurate
measurnients.
-1.5
Using the results in Table 5.1, plot the drain claracteristic curres.
(a)
(iv) Repeat step (ii) io turn for YGs = -0.W, -0.W and
-0.7V.Uz02mA)fl. I rmmI0B MOD
for,fixed vJ« Pcs - - 0.25V for Pcs -0.SV and
Vcs - -0.75V, it is advisable to use (0-1mA)d.c.
-2.0
§UP•5TI0B9
zazasxrz ip fit /5d rizre aad ix adsq«cu escs when
ix sts
*!
-2.5
Ip, mA
u.a. ii '< a‹°u«›a i» >‹ (a•s•a) d• •iza»••ae a
jssifire ro/xct«/F0sarr
gB8\lf’4ttICBt9 0b éZ8itt tbBt'¥Ckfi9t!CS
&0d C0III§3fC }0\II' US\IN(5.
WEEK 2
TITTLE:
DISCUSSION ON THE FIELD EFFECT TRANSISTOR (FET) STATIC
CHARACTERISTIC IN COMMON SOURCE CONFIGURATTION
OBJECTIVES:
I.
II.
III.
To determine the level of understanding in the students from the experiment conducted
To allow the Students express their feelings and observation with respect to the experiment
To have an interaction the lecturer concerned
REQUIREMENTS:
1. Writing materials such as pencils, biros, etc.
2. Student’s jottings i.e what the students must have jotted down during the experiment
3. Relate the experiment to theory thaught
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
2
1.
To investigate the d.c. requéements of a cooanon emitter (CE) Amplifier for proper operation,
d.c. voltage at the collector relative to ground. VBE* *•e
voltage drop between the base, B and the emitter, E while
CE is the voltage drop between the collector, C aad the E
emitter E. For proper functioning of a transistor amplifier,
2.
To investigate the a.c. characteristics of a CE
we expect DOfDlally theft DBE' (0.6 - 0.7)V and Y =
For a traasistor azaplifier circuit to fraction correctly, :t
slould & properly fed Nt6 a d.c. voltage source. In other
words, the circuit must be correctly blased. This means that
be base, emitter and the collector of the transistor in tire
amplifier circuit must be at certain voltage ‘values either
relative to tle ground or relative to one another.
Consider the CE amplifier showa in Fig. 13.1, wherevoltagedivider biasing method is used,
If the d.c. supply vokage * . = 10V, then we expect V =
5V. If these voltage values are maintained in the ampli£ei
cécuit, then the appropriate vdues of (quiescent) d.c. base
current (IB)and tlen (quiescent) d.c. collector current (If)
will be aaiataized ia tbe circuit.
In a CE amplifier, If - Ip (IElS the d.c. emitter current).
At this juncture it is necessary to state that useful fomiuhe
exist by which we can pre-determine the aforementioned
(biasing) voltages, depending greatly on ow choice of com-
ponents Ri.Rt, Rb and Rd. These formulae can be stated as
f0ll0us:
R
Y$isthe d.c. voltage at the base relative to the ground, Yp is Quiescent dc base voltage, (potential dividing of V«by i
& Ri)
the d.c.voltage at the emitterrelativetogroundand V is the
Ri
C2
Ve
B
Rb
“ CE
Fig. 13.1 circuit diagraza ofa CE amplifier.
Vo
R2V$
RTR
Vi
W C(C by- Y0ltJfl
Ouiesceatde base emitter voltage,
BE- B-
E
(13.2)
When Cp is not in circiiitt£e voltage gain A,of the amplifier
is drastically reduced because a phenomenon for
as
- Vt‹ — 5Rt — \Rp
Quiescent dc collector (or eo›itter) cMreat,
I =1
Plitudeof the input signal and
Etc a/Chan yotogj@n
Quiescent dc collector-emitter voltage,
Y
i
Y - ampbto6o othe output s@pB.
(13.4)
If point X and Y are connected, then Rc and Ri be in
parallel although this may not appear obvious ualess an a.c.
equivalent circuit diagram is provided.
(13.J)
If V is thc output voltage when RLi unconnected, then the
output voltage becomes
Here, the word‘quiescent’ refers to d.c. voltage and current
measurements before any input a.c. signal is applied to the
aniplifier,
In this experiment, we shall compare calculated and
measured values of those voltages specified ia Equations
(I3.1-t3J)
made equal to Rc
R s
R
2 wlten L' connected and LiS
=agaitude(i.e. if Rd
Rd).
Dist«ned ooh
Sea a particdar love) (amplitude) of tbe iapyt sigad is
exceeded, a distorted output sigaal is produced wI›icb is
uadesizable.
A,C. C£cractcztetlcs
The a.c. characteristics of the CE amplifier which we shall
consider are tle fo$o g:
o voltage gain A of the amplifier. (voltage gain is t)ie ratio
of the amplitude of the output signal voltage, Vo over the
amplitude of the applied input signal voltage Vi)
o effect of emitter capacitor, Cp on voltage gain.
o edect of external load RLon voltage gain.
o effect of the magnitude of applied input signal on tbe
(distorted) output signal,
o phase relationship between the input - and output -sigad
Y0)(3ggS.
Ideally, we expect the following characteristics with respect
to the amplifier circuit in Fig. 13.1.
For aa undistortcd output sipial the voltage gain of the
amplifier is defined as:
Fig.l32: 180a not-orphan relationship beHecn Y; and
At mid-frequencies within the audio frequency range, the
PROCSDURfi
yudiatedâ Yg, jyy,
D.C. Meaaurtm0nts.
gyp
(i)
aqu épul i iaP out of p#ase with the i°put sig°d ai
p
Zbar, P.B. £‹ ie Electronics,’ A Text - Lab Manual, 19th
Edition, Mc. Graw-Hill, New York,1976, pp. 98 - 102.
Connect the circuit shown in Fig 13.3 and set Vp =
10V. Using a digital voltmeter or AVO meter,
measure +B Vb dBd V‹ 8t QO ts B,E, aad C respectively. Measure V«also.
o NPN transistor type BC 107 or equivalent.
e Resistors 4.7kEI (2 Nos), 3.bk0 , 3b10 , a»d 36 i (all
MW - rated).
o Capacitors 22pF (2Nos)
o Connection lead.
(it)
q$gp$
t Stabilised d.c. power supply unit. FARNELL type LT301 (0 - 30V) or equivalent.
s Sine/Square oscillator. FARNELL type LF-1 0-1 MHZ
or equivdent.
(ml) Apply a 20inV p-p sine wave at 1 KHZ to the input
terminals of the amplifier. Measure the correspondag (uadistortsd) output signd, V usiag aa osciJJo0
o Oscilloscope. Gould OS 255. (0-15) MHZ or equivalent.
o Digital voltmeter or AVO-meter.
Coaaect Cg in tbe circuit but leave out RL »\It of
circuit.
0
â
•
(iv) Disconnect Ce from the circuit and repeat step 5.3.
(x)
Coaagct Csback to the circuit.
$ + V« = 10V
Rl
56it
C1
22,aF
BC107
2#P
5.61
0Y
Wgl33:I'wMeBdmd‹ifsCEamplfes
’f'able 13.1: DC calculated Anti iacnsured values
(ñ)
Coaaect RL t6g ClfCUit byjokdng poiats X had Y
with a coaaection cable aad repeat step (iii).
(vii) Now disconnect Rd frooi tbe circuit.
Yg(yolt) Vy(bolt) Vc(volt)Ie(»A/
Cdculated
Measured
To obtain the measured Ic, use the measured VU d
the measured Vc Equation (13.5)
(viii) Increase gradually the amplitude of the input sink
wave from 20mV p-p unti) a distorted output signd is
noticed on the screen of the oscilloscope (CRO). A,C. Neas«remeats
Measure and record the aniphtude of the input sine
2.
Record all your results in steps (iii), (iv) and (fi).
wave when the distortion just occurs. Sletch the
waveform of the distorted output signd.
’3. Profide properly labelled sketches required ia steps
viii) a»d (x).
(ix) Reduc'e the input signd level back to 20mV p-p and
notice that the distortion disappears.
gUZ5TIOXG
5.10 Keep the input signal of 20inV p-p at 1KHz'and set up
the coiuiection thou in Fig. 13,4 in order to monitor
both the input arid output sigoals simultaneously on
the CRO. Draw to scale the input and output
waveforms observed on the CRO.
(a)
What effect does the change ofRi and Rt have on the
Erasing voltages of the amplifier?
(b)
has capacitor Cp any effect on the biasing of the
amplifier? Giyg your feason? Wky is it desizablg to
connect CE across REV
What effect All a clangs of Vrr have on the operation
of the amplifier ill Fig. 13.3?
(d)
Fig.13.4: Clrcult dlagraoi to demonstrate phase
relationsiilp between input and output signals
R£SULT ANALYSIS
\.
D.C. talculate4 ané measured values.
Using the formulae listed in Equation 13:1 - 13.5 and
component values of resistors Ri, Rz, Rc andRE
given in Fig. 13.3, determineGB, Vp and Vc, (assume
TCE - +iV‹r for your calculation). Fill in these
results into Table 13.1as indicated below.
What, in your opinion, tan cause a distorted otitput
signal if the applied input signal is undistorted?
WEEK 4
TITTLE
DISCUSSION ON THE COMMON EMITTER AMPLIFIER CHARACTERISTIC
OBJECTIVES:
IV.
To determine the level of understanding in the students from the experiment conducted
V.
To allow the Students express their feelings and observation with respect to the experiment
VI.
To have an interaction the lecturer concerned
REQUIREMENTS:
4. Writing materials such as pencils, biros, etc.
5. Student’s jottings i.e what the students must have jotted down during the experiment
6. Relate the experiment to theory thaught
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on the experiment sharing their experience, knowledge
gained and observation.
3
GOMMOH • &AGE AMPLIFIER
1.
To investigate the voltage gain of a common-base
(CB) amplifier.
2.
To investigate the input and output impedance of the
CB amplifier,
BACKGROUND INPORHATION
The most primitive form of the CB transistor amplifier circuit has Wo power supply facilities such as that show in
Fig. 17.1(a).
The‘modern' torm of the CB amplifier looks like a modified
common - emitter (CE) amplifier circuit shown in Fig.
17.1(b). In fact, a common - base amplifier configuration (i.e
earthed base for a.c signals) is obtained from a common emitter amplifier circuit just by connecting a capacitor (C,)
between the base and the earth. Besides, the input terminal
of theNcuit is now between the emitter and the earth.
CI
It should be noted that a NPN - transistor could be used.
instead of the PNP transistor in Fig.17.1(a) and (b).
Cx
r»’
In general the CB amplifier is characterised by very low
input impedance, high voltage gain, and output impedance.
With reference to Fig. 17.1(b), the output impedance of the
amplifier is approximately equal to its load resistance (Rt),
This result is due to the fact that the output resistance of the
transistor is high compared with R,.
In this experiment we shall investigate all the aforementionedproperties of the CB amplifier at some randomly fixed
(s)
Fig. 17.1: Common•base amplifier circuits.
audio frequencies.
Boylestad R. & Nashels , L. Electronic Devices and Cimuit
iJtcoy. Prentice-Hall, New Jersey, 1987, pp. 345 - 348.
The procedure which will be adopted in measuring the input
and output impedances is the same as that described in
detail, in Experiment 15.
Components
Reference
o PNP transistor AC 128 or equivalent
Experiment 15
Havill, R.L. & Walton, A,K, ñ/eiiieitts of Electronics for
Physical Scientist. ELBS & Macmillan, London, 1975, pp. 82
- 85.
o Resistors 1.2kf2, 2.2kf2, 15kf2, 33kD (all MW)
o Capacitors 2.5yF, 10yF and 47yF (all electrolytic)*
• Potentiometers (externally connected) 100f2, Sidi f2and
stO (I linear type). OR Resistance Decade Box
V = -10V
Ri
2.2k
Ct
AC 128
Ci
B
47¿iF
Fig. 17a: Practical circuit diagram of a CB amplifier.
gqulpment
loscope) the resulting output signal (to) across AG.
Record your result as shown in Table 17,1
o Stabilised d.c. Power Supply unit, FARNELL Type LT30-1 0-30V or equivalent
Repeat step (iii) for input signal of the same
« Signal generator FARNELL, Type LF-1 10Hz-1 MHz or equivalent.
amplitude at lkHz and 10kHZ. Obtain tbe corresponding output signal, Vp at each frequency.
Record yollf results.
o fi)sci1loscope GOULD. Type 05 255 0-15 MHz or
equivalent.
Iztpzzt
+ Connection leads.
(v)
PROCEDURE
Voltage gain
(j
(*)
wave across BG. Measure and record the amplitude
of the signal (Vi) across YG.
(«)
connect the circuit shown in Fig. 17.2. Switch on the
power supply unit and set it to Vat = -10V. None of
the potentiometers should, yet be connected in the
circuit. Link up points X and Y with a connection
had,
Connect the signal generator to the mains supply and
switch it on.Set it to produce a 20 mVp-p, 500HZsine
wave. Use the oscilloscope to checl this signal ensuring that it is undistorted.
Apply (Vs) the 20 mV p-p , 500HZ sine wave across
the input terminds BG and measllfe (using the oscil-
Without R in circuit meanwhile (i.e short-circuit
points X and Y), apply (Vi) a 20mV p-p, 500HZ sink
Remove the connection lead between X and Y, (R is
now in circuit)
As you apply the 20mY p-p, 500HZ sine wave (u
before) vary R, gently and monitor the line wave V'
on the CRO. Stop varying R when the amplitude of
V'i is exactly one half of Vi. R is then removed from
the circuit and its resistance value is measured.
Record yow result as shown in Table 17.2.
N.B.
the CB amplifier.)
(vii) Repeat steps (s) an6 fi), EU the frequency ot the 2.
input signal changed to lKHz and 10KHz. Record
your results as before,
Retord the measured input and output impedances
as shown in Table 17.2:
Table 17a: Relationship between input and output
impedance with frequency.
(riii) Remove R finally from the circuit, and link up points
X and Y with a connection lead.
Frequency
500lIz
(ix)
Apply a 20mV p-p,500HZsinewaveacross the input
terminals BG, and measure the output signd Vo
without the load Ry IB ClfCllit initially.
( (Obms)
unpedance
uufil I/iz 4/sforñân d"zsappeazs.)
(Z (Oluns)
(x)
Repeat step(ix) withthefrequeacyofthe input signal
changed to lKHz and 10KHz. Record your results as
before.
(xi)
Switch off the power supply unit and disconnect the
RE8ULT ANALYSIS
1.
Input
iortef, otherw’we rHucethe amplitude ofdie iuyut siyuil
tained.
The potentiometer Ry is ihem r‹nnovedficm the circuit and its resistance value is measured. The
measured value in Ohms equals the output impedanC Zo of the amplifier. Record your result as
show in Table 17.2
Record the data for the voltage gain as shown in Table
17.1.
Table 17.1: Relationship beWeen voltage gain and
(mV)
Vo
(mV)
Yoltage gain
l0kHz
Input
izapedance
N.B. Make cure that the mp I signal produced is uwd'ui-
Next, connect the 5k£1 - potentiometer (Ry) in cirtuit
across terminals AG and vary Ry ntil a new output
signal equal to one hNJin aptitude) of vz ’c ob-
l kHz
3.
From your results instep 2, arc yen convincedthattht
input impedance of the CB amplifier is low at all the
frequencies considered? Comment.
4.
Are your measured values of R significantly different
frown the values of Re (collector resistance)? Coament.
gSSSTIOWG
(a) State the major differences between the circuit
diagrams of a CE amplifier (with voltage-divider biasing) and the CB amplifier in Fig. 17.1 (b).
b)
(c)
If a NPN -transistor were used in Fig. 17.2, what other
modification would you expect in the circuit to ensure
its proper operation.
State one area of application of a CB amplifier.
WEEK 6
TITTLE:
DISCUSSION ON THE RESULT AND ANALYSIS OF
COMMON BASE AMPLIFIER
OBJECTIVES:
VII. To determine the level of understanding in the students from the experiment conducted
VIII. To allow the Students express their feelings and observation with respect to the experiment
IX.
To have an interaction the lecturer concerned
REQUIREMENTS:
7. Writing materials such as pencils, biros, etc.
8. Student’s jottings i.e what the students must have jotted down during the experiment
9. Relate the experiment to theory thaught
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
coxxox. cozzzmo*nxrizcrsnpxzwzn*o**OOn)
'"’
1.
its voltage gain
To measure the input and output impedances of a
is approximately unity, i.e.
,
common - collector (CC) amplifier or emitter fol•
lower.
(iii)
its power gain is much greater than unity.
2.
To measure the voltage gain of tbe emitter follower.
(iv)
3.
To measure the power gain ot the emitter follower.
it exhibits no phase difference between the input and
output signals.
4.
To observe the phase relationship between the input
and output signal voltages in the emitter follower.
BACKGROUND INPOR tATION
It is generally known that, for a common•collector amplifier
the input impedañce is usually hundreds of kiloOhms (typically 100kD - 500kCi) while the output impedance is tens of
ohms (typically 10a - 90Ct).
The common - collector amplifier or emitter follower under
consideration is a transistor amplifier in which the output is
taken from the emitted rather than from the collector, as
slows in Fig. 16.1.
N.B. Readers are hereby remindedthatthe techniques used for
measuring input and output impedante already d’is’•
cwsed in Experiment 15 will also be employed in this
experiment. Therefore, readers may vish to rev’is'e them.
For completeness we state without proof the formulae for
obtaining certain parameters of the emitter follower.
Input Impedance, Z,.
With reference to Fig. 16.1, the input impedance Z; of the
amplifier is determined as the parallel combination of RB
and Zt,.
Ci
i.e.
“
The emitter follower has,some important properties which
can be summarised as follows:
its input impedance is high while its output impedance is low. (Tltis impedance characteristic of the
amplifier makes it useful for impedance - matching
applications).
(16.1)
Vo
Fig. 16.1: Clreult diagram ofa common - tiillector
amplifier or emitter follower
(i)
Zi = Rg | | 2t,
( ie› fe dre parameters of the transistor used in the circuit)
and Zb is the input impedance of the transistor in commoncollector configuration). We note that in practice, ht » > 1
ilnd feRE >
In that case,
hie•
Zb = httRE
Output Impedance, z,
The output impeda c of the amplifier, is determine‹I as
the parallel combination of Rp and @
ie› therefore the resistance Z, is usually quite
fe
smali. Consequently, @ drops well below the value of Rp.
Voltage gain, As
0 Oscilloscope. GOULD TJpe OS 255. 15 MHZ range or
equivalent,
o Conllection lead.
The voltage gain of the emitter follower is giYen as:
Vo
v'
'
o Stabilised power supplyunit, FARNELL Type LT 30-1
(0 - 30Y) or equivalent.
PROCBDURfi
RE
RE +
(i)
anh it is usually (
::)
quite small. Therefore, Av can be assumed approximately
equal to unity if we take Rp > > J. Consequently, Ag is just
close to unity,
As we mentioned above, Z« =
The power gain may be calculated from the experimentally
determined values of input impedance Zi, output impedance
@, input signd voltage Vo.and the corresponding output
voltage, V . Thus:
P; (power in) =
(powerout)) =
(iii)
Connect thg circuit shown in Fig. 16.2 with &ts, A
and B linked by a connection lead. Set Vct to + 10V.
Set the signal generator to produce a 2V p-p, 1
sinusoidal signal (Vi) measured across terminal BX.
Use the oscilloscope (CRO) for your mcilSllfflm0llt of
Vi. Move the CRO probes to measure output Vo
across YX. Record your readings shown as in Table
16.1.
Repeat step (ñ) for frequency Vi Set to, IOKHZ and
100 KHZ. Later, removc the connection lead across
points A and B.
Input Impedance
V0
Power gain =
(iv)
(16.4) (’)
Connect the 1- Mfl potentiometer between pouils A
and B, and set it initially to zero resistance.
Set the signal generator to produce a 2V p-p, 1 KHZ
sinusoidd signd (Vi) across BX. Measure with CRO.
(vi)
With the CRO connected across BX, ittcrease slowly
the resistance of the 1-MW input potentiometer until
the input voltage at tlje input to the amplifier) across
BX is 1V p-p. (just one-hall’ the previous value).
Boylestad, R & Nashekky, L. Electronic Devices and Circuit (*)
R«oy. Prentice-Hall, New Jersey, 1987, pp. 340 - 345.
Remove the potentiometer immediately from the cécuit, measure its resistance, and record it as the value
of J.
References
Havill, R.L & Walton, A.R Elements ofElectronits for Physical Scientists. ELBS, London, 1978 Up. 82- 85.
xnrzeiaie eegumsn
Components
o NPN transistor BC 107 or equiralent
o Resistors 4,?kf2, 1 Mfg (all /-W)
o Potentiometers (linear) lMCi, 500f)
o Capacitors (electrolytic) 4.7pF, 10yF.
(viii) Remove the potentiometer from the circuit and link
points A and B with a connection lead.
(ix) Set the signal generator to produce a 1-K1-IZ
sinusoidal signd (V,).
R.B You are freeto choose lhe amplitude of Yi. However, ytu
should ensure lhut it doe›' not lead to « undistortrâ
output signal,from the amplifur). Measure the niiJpuf
voltage Yq usingthe CRO.
Ci
BC 107
Ct
4.7jiF
4.7k
Flg.162: Practical clrcult flagrant of an emitRr • follower
2.
Record the measured value of the inputimpeda ce at
IKHz.
clip iagor dts*tortiooresults,use a szaaJler aaiplituds
of iztpvt sigad aad repeat tke expeñaeat. Reaove
3,
Record the measured value of tk oatpat impe&nu
at 1 KHz.
tance aad record the yaIye aslJzs oytput izopedaace,
4. (a) If we assume that for the transistor BC IN
used in Flg. 16.2 hie- 1.5k I and h(# " 1t0,
'J Connect a 560-O potentiometer across the output
teraiiiiab YX and adjust it untf it gires an output
voltage just one - hdf the pieriousvalue (i.e V$2). If
the poteatiooieter froza tke circuit zaeasure its resis-
compute Zi and using the formulae given by
Equations 16.1 & 16.2 respectively,
Pkase zelatloaeblp bet 'eea Yi aa4 Yo.
(xi) Repeat step (§),but aoaitor tks iaput sigaal(Yj) and
output tigaal(V«) simultaneouslyon aDouble - channel CRO. Observe and draw the two waveforms obtained on the CRO.
“B£EULT
1.
v0
(volt)
’0
*i
5,
Frequent
IKHz
Frequent
10 KHz
Frequency
100 KHz
2
2
2
Cozapare your ‹ssults itb tbe acasyrcd
values ia steps 2 a«d3.
Compute the power gain of the emitter - follower
tismg JQtidtioh 1b.4. FOf OUf C0II1}3tlt (i0B, Sg t)1C
voltage gain at lKHz from Table 16.1; Z;and Zo Tom
steps 2 d3 respectively.
YGIS
Fill in the data as appropriate in Table 16.1 belt,
V,
( @)
(b)
6.
Draw the waveforifl5 Hi dlld
Obtained Step (xi).
Deduce the phase relatioaslup you notice beWcen
them.
gUS8TION8
(a)
Is the voltage gain o{the emitter follower frequencydependent? If yes, state your reasons.
(b)
How will the resétance value of REin Fig. 16. 2affect
the input impedance (resistance) of the circuit.
II
Draw the waveforms you would expect to see on tâc
CR0 'J the UI $ (Vi)and OULD\It M@ ( o)
were 180' out of phase.
WEEK 8
TITTLE
DISCUSSION ON THE RESULT AND ANALYSIS OF THE COMMON COLLECTOR AMPLIFIER
CHARACTERISTIC
OBJECTIVES:
X.
XI.
XII.
To determine the level of understanding in the students from the experiment conducted
To allow the Students express their feelings and observation with respect to the experiment
To have an interaction the lecturer concerned
REQUIREMENTS:
10. Writing materials such as pencils, biros, etc.
11. Student’s jottings i.e what the students must have jotted down during the experiment
12. Relate the experiment to theory thought
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the practical, mentioning what happened from the first point up to the last point of
the activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
4
ERE@UEHCT REGPOHfiE CHARATTEhIfiTIC OF A GO%%OY
1.
2.
To investigate the frequency response of a conaion
emitter (CE) amplifier.
To investigate a factor that affects the low-frequency
response of a CE amplifier.
BACK.GROUND INPORHATION
One important characteristic of an amplifier is that it does
not amplify an input signal equally at all frequencies.
For illustration, suppose a sinusoidal wave of a fixed
aaipDtude, Vin (say, 5 mV peak - to - peak) is applied to the
input tcrninds of the amplifier but at three different frequencies (say, 200 Hz, 1000 Hz and 10, 000 Hz). Then the
resulting output sinusoidal signd might have ampDtude (V )
say, 10mV, 20mV and 15mV respectively. Consequently, the
voltage gains of the amplifier at those frequencies are as
follows:
At
2fDHz,
gain =
V _ 10aV
=2
At
1000Hz,
gain =
At
10,000Hg gain =
20mV
=4
bmV
=3
JmV
Thus, the voltage gain of an amplifier is frequency - dependant.
The frequency response of an amplifier is a plot of gain
versus frequency (at many frequency pcints). When these
points are connected smoothly, we produce what is genera#y
known as the frequency response curve as shown in Fig. 14.1
Concerning the frequency response curve we take note of the
following:
(i)
The gain •axis is usually expressed in Decibels (dB)
In other words, gain A dB = 20 l0gl0
(ii)
gain A,
dB
3dB
bandwidth = (f2 - fi)
VO
The frequency axisis always expressed in logarithm
scale. This is so because the range of frequencies
evolved in this type ot experiment is so mde that a
linear division of frequencies cannnt accommodate
all the frequencies involved. It is impossible to divide
linearly between l0Hz and ltD,0tDHz except by the
use of the logarithmic scale! There is a graph paper
kawn zs sent - log graph paper which is suitable and
commody used for plotting frequency response curves.
(ui)
Am (dB) is the maximum gain level; it is always
mailed on the gain- axis. A drop by 3 d8 from Am
leads us to another gain level Anno. A straight
horizontal line through the gain level Anno cut the
frequency response curre at to points A and B. A
vertical line fawn points A and B will intercept tite
frequency- axis at frcqucncie› I and f2 respectively.
The difference in value beWeen f2and ft is called the
bandwidth. (i.e. bandwidth = fi-fi).
Fig. 143: Circuit diagram of a CE amplifier.
The shape of the high-frequency response region YB is
normally affected by parasitic capacitive elements of the
nétwork and active device (transistor) or the frequency dependence of the gain of the active device,
The gain versus frequency characteristic can be determined
In this experiment, we shall concern ourselves with the effect
experimentally by using a sine-wave generator as the signal
of C, (tle coupling capacitor) only on the low-frequency
source and an oscilloscope for observing and measuring the
response. In order to study theeffect we shalliavestigatetbe
input and output signak. This arrangement is shown in Fig.
frequency response of the amplifier with to different values
14.2.
of Ct, as show in Fig. 14.4later.
.0stillosto
Sigñal
GeneY8tofi
Amplifier
8oylestad, R & Nashelsky, L. Electronic Devices and Cimuit
f7ieoy, 4th Edition, Prentice-Hall, New Jersey , 1987, pp.
456 - 475.
o HPN transistor BC 109 or equivalent
o itesistors 1k£i (2Nos), 5.6kf2, l0kf2 , 56k0 (all MW)
Flg 14d: Prnctlcal arrangetnenHor measuringamplifler
o Capacitors 0.UF, 22,uF (2 Nos), 80pF.
Now, we should expatiate on our earlier statement that the
gain of an amplifier is frequent dependent and identify
o Signal Generator FEEDBACK FG GO1 (0-1 MHZ) or
equivalent.
amplifier circuit which are res'ponsib1e fpr that characterisuc.
o Oscilloscope GOULD 0$ 255. (0-15 MHZ) or
equivalent.
Let us consider the circuit diagram of the CE amplifier
show in Fig 14.3.
o Connection leads.
frequency- dependent components in a single stage CE
Capacitors Cs. be and CE are the frequency - dependent
components which affect the low-frequency response. In
other words, they affect the shape of the frequency response
curve of F'y 14.1 only in the region XA.
PR0CP•DURE
try can. uhe . :t.a>*.i.r.,.t4.4«itavs,e‹t,
+ 10V and C‹ = 22,uF (initially).
(ii)
*
Connect the signal generator and the oscilloscope to
the mains and switch them on.
+V
- IOV
11
l0k
Flg. 14.4: Practical circuit diagram of CE amplifer
(iii) 5et the signal generator to produce sine wave signal
Vin — 10mV p-p (fixed) at 10Hz. Check the signal on
the ORO in order to ensure that it is actually
sinusoidal and that its amplitud• is 10mV p-p.
(iv)
Use the arrangement shown in Fig 14.2 to amplify Vi»
and measure the amplitude of the corresponding output signfil Vo• RBcoid your result as shown in Table
14.1.
()
2.
With Cci - 0.QF, set up another Table similar to
Table 14.1
3.
Using data in Table 14.1, plot Jhe frequency response
curves on a single semilog graph paper, for CCz =
22,uF and Cci = 0.QF.
4.
Determine the bandwidth of the amplifier from the
hequency response"éurves in steps 3 and 4.
(a)
What is meant by the "frequency response’ of an
Repeat steps (iii) and (iv) at signal frequencies of 14
Hz, 18Hz, 20 Hz, 24Hz, 30Hz, 50 Hz, 80Hz, 100Hz,
500Hz, IKHz, 5KHz, 10KHz, 50KHz, 100KHz,
200KHz, 5fDKHz, 7fDKHz and lMHz.
(vi)
Now, change Cc to 0.UF and repeat steps (u) (vj.
1.
With Cct = 2JF, fdl in the results in Table 14.1
(b)
Sketch the frequency response curve (s) you would
expect if th'e coupling capacitors Cci = ltfJoP. CC,
= UF and Cci = 0.UF are used in turn ion 14.1.
Tsble 14.1: Frequency-response date
Frdquenc
10Hz
14Hz
100Hz
200Hz
500Hz
IkIIz
l0kHz
l00kHz
IMHz
vm (oV)
10
IN
10
10
10
10
10
10
10
Vo{wV)
A = 20 logio
Vin
WEEK 10
TITTLE:
DISCUSSION ON THE RESULT OF THE FREQUENCY RESPONSE CHARACTERISTIC OF THE
COMMOM EMITTER AMPLIFIER
OBJECTIVES:
XIII.
XIV.
XV.
To determine the level of understanding in the students from the experiment conducted
To allow the Students express their feelings and observation with respect to the experiment
To have an interaction the lecturer concerned
REQUIREMENTS:
13. Writing materials such as pencils, biros, etc.
14. Student’s jottings i.e what the students must have jotted down during the experiment
15. Relate the experiment to theory thought
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
5
first measured with no load. The rheostat load is
then connected as shown and adjusted until a new
output signal ’‹›ut is equal to one-half the original
measured value of i’‹›ut- out s then removed from
the circuit and its resistance measured. The measured value in ohms equals thc output impedance
Z„ of the 'amplifier.
In measuring the in put and output impedance
care must be taken to maintain an undistorted
input and output signal.
Power Gain
The power gain of an amplifier is the ratio of
output- to input-signal power.
Power gain
Output and input power may be calculated when
the input- and output-signal voltages and impedances are known. Thus
( 16-4)
R‹iut
(16-5)
R„
Substituting the values of Poutand
we have
Power gain =
in ifl Eq. (l 6-3),
!*‹›u t
( 16—6)
The power gain of an audio amplifier is usually
given in decibels (dBL
Power galfl (d B) — 10 log
Fig. 16-2. Kirchhoff's voltage law applied to the output of
the CE amplifier states that 7‹ ‹ = i,. x P, + v„.
therefore decreases. As i,. decreases, the voltage
across R decreases, and r,.„ increases.
A numerical example will illustrate this principle. Assume P„ = 6 V, R, —— l00o n, and i, varies
sinusoidally between 3 mA maximum and 1 mA
minimum. Assume 2 mA is the steady-state collector current with zero base signal. The outputsignal voltage at the collector will vary from 3 to
5 V as in Fig. I 6-3. It is evident that for an NPN
transistor i,. and v, are 180° out of phase.
For an N PN transistor as the input-signal voltage on the base r;, goes more positive, collector
current increases; as v; goes more negative, collector current decreases. Hence, in the circuit of
Fig. 1 6-2, i, is in phase with v . But we just established that v, (the output signal) is 180° out of
phase with i,. Hence v, is 180° out of phase with
r,».
The conclusion that v is 1 80° out of phase with
v„ is equally true for a PN P CE amplifier.
It is possible to demonstrate this phase reversal
experimentally using an oscilloscope and a sine-
Phase RelaGons
lt can be demonstrated that in the common-emitter
amplifier the output-signal voltage at the collector
v,. is 180° out of phase with the input-signal voltage
at the base •’in- Refer to the circuit in Fig. 1 6-2.
The output voltage v ., from the collector to the
emitter twhich is at ground potential) will vary inversely with the collector current i,.. This relationship can be demonstrated by means of Eq.
( 16-8), which is an application of Kirchhoff's voltage raw to l‹*.<° O tpii
/'r it .
p
i (mA)
2|
jutting P, un tit the voltage i ,. ucre s S A is
470 n
equal to i'„.
AUDIO
OSCILLATOR
TO AMPLIFIER
IN PUT
4. The out put impedance nut If ct C k amplifier
may be measured expei‘imentally by connecting
a rheostat fi„„ IFJg. l 6- l b) as a variable load in
the collector circuit. Struts adjusted u ntil the
load vol tagC ’out equals one-half the no-load
voltage. The resistance of the rheostut then
eQuals the output impcdance ot’ the anaplifier.
5. The power gain of an amplifier is defined as
Power grtin
where R „ and nut tire the know n or measured
values of input and output impcdance. respect ivel y. of the circuit.
6. The power gain of an amplifier is usu‹ill y stuled
in decibe1s t‹1B):
Power gain (d B) — l t4 log ' "'
’out
lbs
Fig. 16-4. Diode rectifier with input and output waveforms.
wave input with external sync/trigger as in preceding experiments. It is also possible to determine
experimentally the phase relationship between the
input and output signals in a CE amplifier using the
test circuit shown in Fig. l 6-4s. The diode rectifies
the audio signal injected by the AF generator. The
rectified waveform appearing across the 5000-f1
load is shown in Fig. 1 6-4b. This negative-going
waveform is now injected into the base of the
grounded-emitter amplifier. The output waveform
is then observed on an oscilloscope at the collector. A 1 80° phase reversal will appear on the oscilloscope as a signal reversal, that is, as a positi vegoing waveform. The amplifier must not be overdriven during this process.
SUMMARY
1. The input impedance Z „ o R; of an amplifier
is defined as
R in
’in
where v„ is the signal voltage on the base and
i „ is the signal currcnt in the base.
2. N;, may be determine‹1 experimentally by measuring v; and i; and computing their ratio.
3. £;, may also be computed by inserting a rheostat ñ,. in the base circuit as in Fig. l 6- 1, injecting an audio sine wave into the base, and ad100 Basic Electronics
7. 1 n a C E amplifier the out put-signal voltage at
the collector is 1 80° out of phase with the inputsignal voltage at the base.
SELF.TEST
Check your- understanding by answering these
questions.
I . I n Fig. l 6- 1 R ,. is adjusted until the voltage
U „, — U„, . To find the input impedance of the
amplifier it is neces sary io measure the
of
*. In dig. I 6- 1 , f'„ — 0.5 V,.q„ U , = 1 V,q„ and
R ,. — 1000 D. The input impedance of the
amplfier is
f1.
3. The rms voltage measured at the collectoi of
the amplifier in Fig. 1 6- 1 ri is 4.6 4' without
load. When a 250-0 load is connected act oss
the out pu i. the rms voltage measured at the
collector load is 2.3 V. The output impedance
of the circuit is
II.
4. An oscilloscope. externall y li‘igSeied by the
output signal at the collector of Fig. 1 6- I and
connected to observe the input signal › „ , is ‹adjusted to show a sin31e sine wave, whose positive alternation leads the negative al1CI’nation.
When the oscilloscope is connected ft om collector to ground, the
alternation of
the sine wave observed on the scope le‹ids the
alternation by
deli ees.
5. I f the rectified out put i „„ of Fig. 1 6-4 b is injected into the input of Fig. 1 6- 1 n. the waveform observed with an oscilloscope at the collector will be a
-going rectified si ygnal
voltage.
WEEK 12
TITTLE
DISCUSSION ON THE RESULT OF THE FREQUENCY RESPONSE CHARACTERISTIC OF THE
COMMOM EMITTER AMPLIFIER
OBJECTIVES:
XVI. To determine the level of understanding in the students from the experiment conducted
XVII. To allow the Students express their feelings and observation with respect to the experiment
XVIII. To have an interaction the lecturer concerned
REQUIREMENTS:
16. Writing materials such as pencils, biros, etc.
17. Student’s jottings i.e what the students must have jotted down during the experiment
18. Relate the experiment to theory thought
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
OBJDC¥IPEB
1.
2.
with amplifier factors (for transformer
To determine the d.c. power dissipated by the
amplifier.
To investigate the relationship between load resistance Rg and efficiency, q of the amplifier.
To ver
that the maximum possible efficiency, q of
the amplifier is less than 50%.
amplifiers) such as:
(i)
d.c. power dissipation by the amp
(ii)
power efficiency of the class-A ai
(iii) impedance matching to the resist
D.c. power dlnatpatlon by the as
Fitst, we should determine the input d
Bipolar junHidn transistor amplibers can be classified in
different wa One of such way is according to claxs e.g.
Class A, Class B, Class AB and class C. Class A amplifiers,
ia turn, cao be sub-divided into series-fed class-A amplifier
and transformer-coupled class A amplifier, A series - fed
class A amplifier has characteristically low efficiency (its
maximum possible efficiency does not exceed 25%) while
transformer-coupled class A amplifier bas a higher efficiency(its maximum possible efficiency’is notgreater than 50%).
Later on we shall define efficiency and explain how its value
can be calculated! At tbis stage, we skall coacera ourselves
tained from the dc power supply unit (V
current, Ip from the supply unit. Therei
to Fig. 20.1 we can calculate Pi(d ) as:
i(dc) -
cc !Q
where, Vp = d.c. supply voltage
Up - d.c. quiescent @llector ciii
co can be practically determined by mea
a.c. input signal is applied) when a d.u
nected between the terminals X and Y.
Nr: Nt
EC 109
No > N2
10fyiF
OV
Fig. is.i: Schematic circuit diagram of a transformer-coupled Class-A amplifier
Next, assumiisg aa ideal.. traiisfoitnér, the a.c. power, (Pq„j)
developed acid the iaaasfbmzer
power, (Pi) &1i
The. Jr
to the load..
A also :tAe a.c
Ni
*=
Nz
= step-down turns ratio needed to make the
load resistance appear as a lafgér effective
resistance seen from the treesformcr primary.
across the foafi can be expressed as:
For Tx;lmp1e, the effective resistance (R‘;_) seen Eroding into
the primary .of ,a IS:1 transfocrmer uu acted to .an ootpiit
Rc
where VL ^ ibe rois of the ac voltage across ,the :W
foraicr secoadazy.
load of 40 is obtained as:
Nr"
3
. RL =. Lbe load resistor acro8s tbr rraosfozazcrse‹x›a-
dary ceriz›iaals.
Gooscqn0ntly, for the transformer-coupled ampliEer the
oaly power lost is that dissipated by .the: power transistor
(are ti•c coflccior - cminer junction) as ‹alcuisted by the
folioseing equation:
where Pg - power ‹dissipated (as heat) by the amplifier.
15 4 = 0.9kO
Proai the foregoing, we can dcduue ibat diffcrmt Rp leads
tn different Valués of R'p and flown Equatim %J this reads
consequence to different Pqp). However, there is a •
.ti‹;uIar load due, RLFch ca•pt‹›dum - $o{uo)
a•dm•x rum efficiency,of the amplifier.. (as shown inP-quiIncidentally, one of oiur tasks in this experiment iS to dctermiisthc load resistance (Ri) which gives m•*••'iuinefficico-
Power e&cicocy of the class - A amplifier can be calculated
Boyteitaii, R.. iad Nashglslty, L. 2ffecfzonic Zie4icnr wild Circuit 77izoJ. Prentice - Hull; New Jerseyi 1987, pp. d03 - M.
where Pgpj and Pi(gt) arc obtainable from Equations 20.Z
For a class - A transfoimer-coupled amplifier, the mszimnm
tbeorc0cal efficiency is. 50%. This is one of the claims we
s
Lurch E2'J. FundArncnrafs ‹if£ieceo tics. 3rd Edkio•, 3ohn
Wiley, New York, t96J, pp. 352 - 354.
NPN transistor BC 109 or equivalent
• Resistors”1JcL2, 33kU, 220k62 (eacb MW)
The resistance seen looking into the primary of the traasformet is related lo the resistance connected aiross the
secondary. T£e ratio of sccnndnry resistance io primary
resistance may be expressed as:
Rc’
N2
,
o Capacitors, (Electrolytic) lQuF (16V), l0tjrF (10Y)
• Audio frequency (Step-down) transformer. RS Gtoi:k No
21?-567 or equivalent.
o Stabilise.d.: d.c. po.wcr siipp.Iy. FARNELL LT 30-1 or
equivalgnt
o AVO meter
wbere RL
Resistance of load conncclnd across the
transformer secondary.
R'p = Elective r+sista•ce seen looking into
transformer primary.
• Oscilloscope.GOtlLD OS 255 or equivalent
• Sice/S qu are wave oscillator PARNEnc or- i or
equivalent
e Resistance Decade Box. Type JJ.
(vi) Next, re-connect the amplifigr circuit to -1- Voc (1.e,
.+ 10V) d.a, supply and pass the signal wa.reform V;
o Coa»ec6o Lead.
set the AVO eieter to read dc curient'and co•nca it
between terminals X and Y.
Increase tho signal amplitude Vi gradually from the
10mV until you just begin“ to observer a clipi›ed (distorted) output' voltage Vi_(p.gpj across A-B. Now,
measure and record t1ie;ampbtudes of the new i•put
(Vi) and output signals Y -p).
lfiBi Reñieinber, Pa(xc) =
, VL(rms) =
.
:Meafiure.und recoFd.l£iQ and Vq• (Repeat the cns•
tance,'Rj set on the resistance decide box'to'4£2, 6£1,
8D; l0f2, 2tM, 40d, and 3£Of2 in turn, and mcerd the
corresponding Vi and Vp
f#Bf#lCac)=fCgFw
(iv) &wlkuho8Mopoumrsup§yedrssxwcMeAVO
decade bi›x iicrna terminals A-B and set it to RL =
1 Record iir eieasured‘values I and V Calculits
your dissipated power Pity) once and.for all.
2.
Record all you i easured values ofV . and Vigil
and Yyyy fin varying Rr in steps (vi) - (viii. Calculate tbe corresponding P tee) and Po (using Equations 20.2 and 20.3 as set.out in Table 20.1.
cigiul generator to pioduce xinmvo,. (Vi), l0mV
occilloscopc (GIRO). Mea while, diaco0occt the
CñO from the circuit.:
’
T tile 20.1: Power dlsalpeicd by the umpllfler
Lzmd resistance
2
4
3.
Usiag your aieasurcd vatxss Of VL{zas) Ie varyñzg
Rr. caIotIat< tbc afbci•acy of tk• atapl¥ ›r, y a• set
2
8
10
(a). Comment on the relationship between the lend resistance Rr and Pp(se) as obtained Table 20.1. Docs
4.
From tfie data in Table 20.2, determine the load resistance value Mwhich gives mnzimum eEkicncy of the
5.
Check Table 20.2 to sec whether of not the elficiency,
p exceeded S0% fur any value of Rs
If 'the 'audio ’frequency transformer were removed
coaipl*tcly from the circuit and the eolieaor load
were replaced by RL (previous}y rrinnemed acfosi
terminals A-B) would you expect the efficiency of the
azopliñer to iztcreuse or decrease io caasequcacc2
Comz•cnt bAoDy oo your xaswcr.
WEEK 14
TITTLE:
DISCUSSION ON THE RESULT AND ANALYSIS FOR THE TRANSFORMER COUPLED CLASS A
AMPLIFIER
OBJECTIVES:
XIX.
XX.
XXI.
To determine the level of understanding in the students from the experiment conducted
To allow the Students express their feelings and observation with respect to the experiment
To have an interaction the lecturer concerned
REQUIREMENTS:
19. Writing materials such as pencils, biros, etc.
20. Student’s jottings i.e what the students must have jotted down during the experiment
21. Relate the experiment to theory thought
PROCEDURES:
 The lecturer should start by given a general introduction of the discussion on the experiment
.
 A general summary of the pratical, mentioning what happened from the first point up to the last point of the
activities that took place during the experiment
 The lecturer should allow the students to give their on contribution base on their understanding.
 Finally, the students should be given chance ask questions, where the students will be asking question
associated with the experiment
ASSIGNMENT:
. An assignment should be given to students to write report on experiment conducted, sharing their experience,
knowledge gained and observation.
EAPERlMEMT
Push-pull Power Amplilie:r
d&lECTtVES
1. To define class. B operation
2. To connect and st.gnat-tr.ace a pus:hop.ull audio
‘° power afliplifier
class B. Curre'nt bows for more than '180° but less
than 360', as i r i z. *a- i ‹•. I t is clear from the current waveforms tr.« ir « ingle transistor operating:
into a rexistive told were biased class B or AB,.
signal distortion would ace ur. A pu'sft-pull circuii
INTRODUCTORY INFORMATION
Class B Operation
High-power audio systems require .more audio
power than a single outpui stage can provide. One
solution is to use two or more transistors connected in .push-pull. Push-pull amplifier circuits .are
operated either class B or class AB..
In the preceding experiment we learned that in
class A operation the erriitter-base section of ihe
transistor is forward-biased for the entire period of
the input signal. Current flows for 360° and the
output is undistorted, as in Fig. 22-1 rr.
In class B opera:ti'on, the emitter base of a lransistor is forward-biased by the signal during onehalf of the input signal an'd reveise-biased during
the other half. The. collector-current waveform of a
class B circuit appeam as in Fig. 22- I b. Note that
current bows for approximately 180° and is cut off
during the remainder of the cycle.
Class AB operation lies between class A and
Push-pull Amplifier
When biased foi‘ class AB or ciass B operation.
push-pull output urnplitiers can handle a signal ampIitude approximated y t w ice as large as lhat nf a
conventional class A poxs'c r amplifier. For this
reason .c]ass 8 and class AB output siages can
deliver mure po\v.er than a single-ended class A
stage.
A push-put 1 output .stage is shown in Fig. 22'-2
@.. and @„ are output iransistors connected as
common-emitter amplifiers in a balanced circuit.
T.. an input transformer. couples 9,. called the
driver. to stages O: and Q z.
The bases of Q.. and .@, are connecied to the
ends of the CT secondary of T.. Hence ihe bases
receive two sis••!s. cqual in itmpli£ude but 186'
oul of pfiase. For a line-wave input, the base of Q
will be positiv e when the base of J„ is negalive.
When 9.. swings negative. the base of @, goes positive. As. a result. when current flc •s in the collector of @.., n0 Current flows in Q,. ancl vice versa.
The collector currents of g„ anJ g, Row in op-
posite directions through the primary of T . the
output tr¿»sfcrmer. Suppc.se the magnctic field
\fiat the collector current of @ sets up about the
primary is expanding whe.c collector current in g.,
is increusing. At Ibe same time collector current in
@, is decreasi.ng, and tfie resulting magnetic field is
moving in the same direction as the fietd arising
from @... Thus the fields aid and ipduce a larger
emf in the secondary than either could alone.
:Q.. -and @„ are .two medium-power t ransistors,
operated close to c]as 9 B, with just enough forward
bias l supp|ied by. R, ’and the comtiination of ft,; and
A. j to cause .a small collector idling current In how
Ag. z2-‹. Current waveforms in lay ttass A, (d} «lass B, (d)
class AB amplifier.
in /.. and g7., which prevent cmssox'er Jistonion.
The waveform in Fig. 2-'-1 shows the distunion
which occurs when traijsisturs in a push-pull staye.
6. A C E amplifier has a voltage gain of 50, an
input impedance of 1 000 Al, and an out put
impedance of 2fJt) iL The pou.'er gai n of this
amplifier is
7. The decitael power gain of the amplifier in question 6 is
d B.
MATERIALS REQUIRED
■ Power str ppl y: Variable regu lated low-voltage dc
so rce
m Equipment: Oscilloscope; EV M: AF sine-wave
generator
■ Resistors: '/z-W 470-, 56t)-f1, two I -. 4.7-, 8.2-,
I 8—k I
■ Capacitors: Two 25-QF 50—V; l 00-QF 50-V
■ Semiconductors: 2N 6004; I N 41 ñ4, or equivalent
■ Miscellaneous: SPST switch ; 2-W 5ooo-n potentiometer
PROCEDURE
Input Impedance
Power Gain
1. Connect the circuit of Fig. 1 6- 1 o . Note that fi ,
is a 1000-f1 res istor, not a potentiometer.
2. Power on. Adju st the A F sine wave generator
for 1 000 Hz ‹ind set the generator Seve J
(output) control for 70 percent of iiio-iivium
iiii di.s touted oil tpat, i'„„ as observed with an
oscilloscope ccinnec ted across the out put.
With an oscilloscope. measure and recorcl in
Table I 6-1 the peak -to-peak vol tage a. v„
across A C. b. >„, or r„ across BC. and c.r„u,
in the output.
4. Compute i ,. across R . by sub trac ting t „, from
i .„ . Record in Table 1 6- I . Compute and
record i„ and II „,. Show your‘ computations.
Output Impedance
7. Co rnpute and record in Tablc I 6-1 the voltage
gain and power gain (in decibels) of the circuit
under load. Show your computations.
Effect of Unbypassed Emitter Resistor
8. a. Do not chair gr tlir le vel nf the inytit .si gnal.
Remove bypass capacitor Cz from the circuit.
With an oscilloscope observe the output signal
i'„,t. Why has the output of the amplifier
dropped so dramatically?
b. With C, still out of the circuit, increase the
generator output until you, Equals 1 V p-p. Repeat steps 3 through 7.
Phase Relationship
5. Do itot i ‹i rv th‹• ink tit-siquail /e ‹•/. C.on nect a
5000-D rheostat 6„„. as in Fig. 1 I›- I h. across
the output. Adjust R„„, until the measui cd
outpul signal v„„ equ ‹its one -half the out put
measured in step 3c.
6. Re mo›'e ñ„,t fro m th e ci rcuil. M ensure and
record its resistance . This is the value or the
output impedance „R u , of the amplifier.
NOTE: The output impedance of the amplifier is not
a fixed quantity: it depends on the load resistance
and transistor voltages.
9. Power off. Remove R from the circuit and
conncct points A to B. Connect the half-wave
rectifier circuit shown in Fig. 16-5. The
1000-H z signal from the generator is coupled
to the in put of the half-wave rcctifier. Thc
output of the half-wave rectifier is connected
as the A F signal source for the CE amplifier in
Fig. 1 6-1 .
10. i'ower on. Reset the signal generator so that „
is at thc same yr«k-ve›/zr/ye level as in step 3b.
11. With an oscilloscope observe two cycles of the
TABLE 6- . CE Amplifier Impedance and Power Measurements
V p-p
?-7
Gain
relation lips in the cii cuit of Fig. I ñ- I . Follow
AUDIO
TO INPUT 0F
AMPLIFIERS FIG 16 \
QUESTIONS
I, (‹i) I I yuu wished la me SUFC ›',. (8’0tl?l/C itCI“0S8 @ ,')
fig. 16-5. Adding signal rectifier to experimental groundedemitter amplifier.
TABLE 16-2. Phase RelationS in CE Amplifier
4.
input signal waveform. Draw this waveform in
Table [6-2.
12. Observe no cycles of the output waveform.
Draw them in proper time phase wlth ltte inpul
in Table 16-2.
cd11 iu any substanliatinj9 é‹ita in 1his experiment,
13. Explain in deiall a method, other than the oce
USCd IO this procedure, for deterninin/ ‹h‹ Answers t0 Self-Test
input impedance of a CE amplifier. Follow this tptypp g
procedure and record your results.
a §gg
)4. Explain in detail a method, other than the one
j ¿Jr
used in this procedure, for vcrify›ny the phase
4. cj›rvr. pa ir ’r. IXU