SECOND SEMESTER, 2021/2022 SESSION
EEE 244: ELECTRONICS III
FOR HND 1, COMPUTER Engineering
Lecture 5
PREPARED BY ENGR. S. A. FADARE
1
PRESENTED BY ENGR. B. A. OJO
The federal polytechnic, ilaro, ogun state, nigeria
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
RC PHASE SHIFT OSCILLATOR
RC Phase shift oscillator is another sinusoidal oscillator. Its circuit diagram,
feedback factor formula and frequency of oscillation formula are showat the
other half of the slide.
Mode of Operation
Its mode of operation is similar to positive feedback amplifier that satisfies
Barkhausen’s criterion.
The transistor amplifier in its circuit serves as the internal open loop amplifier
for the oscillator.
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EEE244
LECTURE 4
The three RC circuits that are coupled together forms the feedback network. The
output signal of the transistor is coupled to the feedback network circuit input as
E0 and the feedback signal appears at the input terminal of the amplifier as Ei .
For the 3600 phase shift of the input signal, the amplifier produces output signal
that has 1800 phase shift to the input signal. Each RC arm of the feedback
network do 600 phase shift of the output signal as its passes through them to be
fed back to the input signal. Therefore, the feedback network circuit produces a
feedback signal that has 1800 to the output signal and 3600 phase shift to the
input signal.
𝐸𝑖
𝐹𝑒𝑒𝑑𝑏𝑎𝑐𝑘 𝑓𝑎𝑐𝑡𝑜𝑟, 𝛽 =
𝐸0
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
WIEN BRIDGE OSCILLATOR
It has a two stage amplifier circuit configuration with Wein bridge
rectifier at its input terminal..
The first amplifier works as a positive feedback amplifier using
transistor T1 as its internal open loop amplifier. The positive feedback is
fed through series R1C1 and parallel R2C2 to the input of transistor T1.
Both RC circuits determine its frequency of oscillation.
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EEE244
LECTURE 4
The second amplifier works as a negative feedback amplifier to
ensure constant output signal. The negative feedback signal is
derived from R6 R7 voltage divider circuit at the input of transistor T2
through the assistance of the temperature and current sensitive
Tungsten Lamp L3. The resistance of L3 increases with current. So as
the output signal tends to increase, more current will be fed into R3 L3
arm of the bridge rectifier, which causes resistance of L3 to increase.
As a result of this, the negative feedback increases via R6R7 voltage
divider circuit and return the output to the expected constant value
(stabilize the output).
This makes it to be a reliable sinusoidal oscillator free from fluctuation
and effect of ambient temperature. Usually, it is used in audio RF
oscillator.
Though, it uses both positive and negative feedback, the total phase
shift of the feedback signal relative to input signal is 3600 via the 1800
phase shift provided by each transistor.
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
SOLVED PROBLEMS ON RC PHASE SHIFT AND WIEN BRIDGE
OSCILLATOR
1. A 1800KHz RC phase shift RF oscillator was used as base RF oscillator for a radio transmitter. If
the selected capacitance for capacitor of its RC feedback network is 5pF each, what would the value
of each resistor.
Given Parameter: f0 = 1800KHz;
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EEE244
LECTURE 4
𝑓0 =
1
2𝜋𝑅𝐶 6
𝑅=
1
2𝜋 𝑋 1800 𝑋 103 𝑋 5𝑋10−12 𝑋 6
→𝑅=
C = C1= C2= C3= 5pF ;
R = R1= R2= R3= ?
1
2𝜋𝑓0 𝐶 6
Ω → 𝑅 = 7219Ω ≈ 7200Ω
2. An RF transmitter has a 800 KHz Wien bridge RF oscillator. Both the series and parallel RC
circuits of the Wien bridge’s feedback network use equivalent capacitors of 250pF each. Calculate
the resistance of each resistor at both RC circuits.
Given Parameter: f0 = 800KHz;
𝑓0 =
𝑅=
1
2𝜋 𝑅1 𝐶1 𝑅2 𝐶2
=
1
2𝜋𝑅𝐶
→𝑅=
1
2𝜋 𝑋 800 𝑋 103 𝑋 250 𝑋 10−12
C = C1= C2= C3= 250pF ;
R = R1= R2= R3= ?
1
2𝜋𝑓0 𝐶
Ω → 𝑅 = 795.77Ω ≈ 800Ω
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
DIFFERENT TYPES OF OSCILLATOR WAVEFORMS
Waveform is the graphical display representation
of a typical electronic signal.
The cycle of a waveform can be described is a
unique graphical pattern that is repeated
consecutively and sequentially.
The Period of a waveform (T) can be described as
length of time in seconds that a cycle of a wave
occupies.
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EEE244
LECTURE 4
The frequency of a waveform (f) is the amount of
cycles of the waveform that is occupy in a unit
length of time which is basically one second.
A waveform’s cycle is divided into active or on
region of its period (TON) and inactive or off region
of its period (Toff).
Duty cycle of a waveform (D) is the relative
percentage of the time length of on active
period (Ton) to the total period of the cycle. It is
usually express in percentage or fraction.
𝑇𝑜𝑛
𝑇𝑜𝑛
𝐷=
=
𝑇𝑜𝑛 + 𝑇𝑜𝑓𝑓
𝑇
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
MULTIVIBRATOR
EEE244
LECTURE 4
6
Multivibrator can be defined as an electronic
oscillator circuit that produces non sinusoidal
waveforms at its output.
Transistor based multivibrator is usually a two
stage amplifier that output signal of one amplifier
serves as input signal to the second one.
There are basic three types of multivibrator base
states of its output waveform:1. Monostable Multivibrator
2. Bistable multivibrator
3. Astable Multivibrator
Monostable Multivibrator: It is also called one shot multivibrator. It
has one stable state and one quasi-stable state (half stable). The
application of pulse to the trigger terminal causes the circuit to go into
quasi-stable state for a period determined by the time constant circuit.
After that quasi stable state period, the Monostable multivibrator goes
back to its stable state. This process is repeated any time the trigger pulse
is applied. It is called a one-shot multivibrator because it produces a
single pulse at the output for each trigger pulse input.
Bi-Stable Multivibrator: It is a multivibrator that has both states stable.
Hence, it is called flip-flop multivibrator. It requires the application of
external trigger pulse to change from one state to another. A trigger pulse
produces a half-cycle of square wave output while the next trigger pulse
produces the other half-cycle of the square wave output.
Astable Multivibrator: It is a multivibrator that automatically and
continuously produces alternate states of the multivibrator for a period
determine by its time constant circuit. It produces the output non
sinusoidal waves without trigger input signal. Hence, it is also called free
running multivibrator.
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
TRANSISTOR BASED MONOSTABLE MULTIVIBRATOR
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EEE244
LECTURE 4
Transistor based monostable multivibrator is a
two stage transistor amplifier with output signal
of one stage amplifier in a stable state and the
state of the output signal of the second
amplifier is in a quasi-stable state.
As shown in its circuit diagram, as Vcc is applied
(with no trigger pulse signal applied) Q1 will be
in stable cut off state and Q2 will be in stable
conducting (ON) state. Monostable
multivibrator is now at stable state.
As pulse trigger is applied to the base of
transistor Q1, transistor Q1 switch to ON state
and transistor Q2 switch to OFF state for a
momentary period equal to time constant
T1=0.693R2C1. Both will remain in this semi-stable
or quasi-stable state till the expiration of period
T and return to permanent stable state.
As next trigger pulse is applied, both transistor
will alternate their states momentarily again
and return back to permanent stable state.
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
TRANSISTOR BASED BISTABLE MULTIVIBRATOR
Transistor based bistable multivibrator is a two stage
transistor amplifier with output signal of one amplifier
stage connects to an RC circuit and input terminal of the
other amplifier stage, and as trigger pulse signal is
applied each transistor produces a stable output signal
that is opposite to the output signal second transistor.
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LECTURE 4
As initial pulse trigger is applied, transistor Q1 switch to a
stable ON state and transistor Q2 switch to a stable OFF
state. Both will remain in their state permanent till another
similar trigger is applied.
As next trigger is applied, both transistor will alternate
their states – transistor Q1 switches to OFF state and
transistor Q2 switches to OFF state.
Hence, each transitor produces one part of the cycle of
the output signal via the assistance of the first triggering
signal and the second half of the cycle when the
second triggering signal is applied.
Therefore, the bistable multivibrator is called a flip-flop
because of its alternating output signal (ON and OFF) as
triggering signal is manually applied.
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
TRANSISTOR BASEDASTABLE MULTIVIBRATOR
Transistor based astable multivibrator that is
also known as free running multivibrator is
comprises of a two stage transistor amplifier
Q1 and Q2 that automatically produces
alternate output without any triggering signal
applies to any of the transistor.
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EEE244
LECTURE 4
The oscillating frequency is determined by
two internally incorporated RC circuits
R2C1and R3C2.
Both transistor are always in alternate states –
when Q1 is driven into saturation by the
output signal from Q2 , transistor Q2 will be in
off state while Q1 is in active (on) state. Vice
versa, when Q2 is driven into saturation by the
output signal from Q1 transistor Q1 will be in
off state while Q2 is in active (on) state.
ON Time for Q1= OFF Time for Q2 = T1
T1=0.693R2C1
OFF Time for Q1= ON Time for Q2 = T2
T2=0.693R3C2
Total Time Period of the square wave = T
T= T1 + T2 = 0.693(R2C1+ R3C2)
For symmetrical transistor based astable
multivibrator:- C = C1= C2 ; R = R2 = R3.
Therefore ,
T= T1 + T2 = 0.693(R2C1+ R3C2)= 1.386RC
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
UJT BASED MULTIVIBRATOR
UJT oscillator is a sawtooth waveform oscillator. It has its applications
in relaxation oscillator and triggering circuits for control switching.
Its simple mode of operation is based on capacitor C that charges
exponentially to its peak voltage through R1 (just like a basic RC
timing circuit) as voltage VBB is applied.
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At the peak point voltage of capacitor C, E-B1 junctions switch into
lower resistance conduction mode and start discharging the
capacitor C. As C is discharged to zero, the exponential charging
process starts again and repeat the process of charging and
discharging to produce a sawtooth waveform at frequency
determines by the R1C circuit.
EEE244
LECTURE 4
Frequency of oscillation for the sawtooth waveform output =
1
𝑡
𝑖𝑛 𝐻𝑧
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
555 TIMER IC BASED MULTIVIBRATOR
555 timer IC is an 8 pin DIP (Dual Inline
Package) IC (Integrated Circuit) that is used
to generate pulse or square or rectangular
wave. Please take note of the pin layout and
name tag of each pin.
555 Timer IC can be configured and operated
in two modes
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EEE244
LECTURE 4
1. Monostable (on shot) Multivibrator mode
Ground
Trigger
Output
1
8
2
7
3
6
4
5
2. Astable Multivibrator mode.
Furthermore, just like other oscillator, RC circuit
time constant contributed to frequency of
operation on the duty cycle of the output
wave.
Reset
Voltage Supply
(VCC)
Discharge
Threshold
Control Voltage
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
555 Timer IC Based
555 Timer IC Based Astable
Monostable Multivibrator
Multivibrator
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EEE244
LECTURE 4
Monostable multivibrator produces just a single
for each applied trigger for ON time period = T
TMono = 1.1RC
The period T is called Tmono to avoid confusion
with the astable mode on time periods.
Remember frequency is reciprocal of period
1
𝑓=
𝑇
Remember Duty cycle, 𝐷 =
𝑇𝑜𝑛
𝑇𝑜𝑛 +𝑇𝑜𝑓𝑓
=
𝑇𝑜𝑛
𝑇
ON Time for the output wave = TON = 0.693R1C
OFF Time for the output wave = TOFF = 0.693R2C
Total Time Period of the square wave = T
T = TON + TOFF = 0.693(R1+ R2)C
For symmetrical 555 Timer IC based astable
multivibrator:- R = R1 = R2. Therefore ,
T= TON + TOFF = 1.386RC
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
1. SOLVED PROBLEMS ON MODULE 3
1
A symmetrical transistor based astable
multivibrator has its two capacitors to be 10nF
and two resistors 10KΩ.
(i) Determine the period and frequency of its
output waveform
.
(ii) Sketch two cycles of its ideal output
waveform
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EEE244
LECTURE 4
The frequency of its waveform, 𝑓 = 𝑇
1
𝑓=
𝐻𝑧 = 7.246 𝐾𝐻𝑧
0.138 𝑋 10−3
(ii) Two cycles of the output waveform
0.069
mS
0.069
mS
Given Parameter: C=C1 =C2 =10nF =10-8F;
R =R1 =R2 = 10KΩ = 104Ω
(i) The period of its output waveform,
T = 0.69(R1C1 + R2C2) = 1.38(RC)
T = 1.38(104)(10-8) S = 1.38 X 10-4 S = 0.138mS
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
2. SOLVED PROBLEMS ON MODULE 3
Design a monostable 555 timer multivibrator for
digital system button that will allow control from
the button after five seconds the button is pressed
to produce another output. The button produces a
10% duty cycle negative going pulse to give an
output of 75% duty cycle. Use a100 nF capacitor
for your design. Draw your final circuit diagram.
EEE244
LECTURE 4
∴𝑅=
𝑡𝑝𝑜𝑢𝑡
3.75
=
𝛺
1.1𝐶 (1.1)(10−7 )
R= 34090909.09 𝛺 ≈ 34𝑀Ω
Given parameters:
14
𝐷𝑒𝑡𝑒𝑟𝑚𝑖𝑛𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑡𝑖𝑚𝑖𝑛𝑔 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟
𝑡𝑝𝑜𝑢𝑡 = 1.1𝑅𝐶
The period of oscillation, T = 5 seconds
Duty cycle of the input , Din= 10 %
4
Reset
VCC
8
7
Discharge
Output
3
6
Threshold
Control
5
2
Trigger
Ground
1
34.1MΩ
Duty cycle of the output, Dout = 75 %
The timing capacitor, C = 100 nF =
10-7
Determination of the output pulse width
𝑡𝑝𝑜𝑢𝑡 = 𝐷𝑜𝑢𝑡 𝑇 =
75
100
VCC
Output
Signal
100 nF
Input Pulse
from digital
button
5 𝑆 = 3.75 𝑆
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
3. SOLVED PROBLEMS ON MODULE 3
a) Provided you are given a 1000 pF capacitor,
design an astable 555 timer multivibrator with
an oscillation frequency of 100 MHz and a duty
cycle of 75%..
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EEE244
LECTURE 4
Determining the ON period for the output waveform
75
𝑇𝑂𝑁 = 𝐷𝑜𝑢𝑡 𝑇 =
10−8 𝑆 =
100
7.5 𝑋 10−9 𝑆 𝑜𝑟 7.5 𝑛𝑆
Determining the OFF period for the output waveform
Given parameters:
𝑇𝑂𝐹𝐹 = 𝑇 − 𝑇𝑂𝑁 = 10 𝑛𝑆 − 7.5 𝑛𝑆 = 2.5 𝑛𝑆
The frequency of oscillation, 𝑓0 = 100 MHz =
108 Hz
Determining the lower bias resistor, R2
Duty cycle of the output, Dout = 75 %
𝑇𝑂𝐹𝐹 = 0.69𝑅2 𝐶
∴ 𝑅2 =
The timing capacitor, C = 1000 pF = 10-9 F
𝑇𝑂𝐹𝐹
0.69𝐶
=
2.5𝑋10−6
0.69𝑋10−9
𝛺 = 3.623188 𝛺 ≈ 3.6 𝛺
Determining the upper bias resistor, R1
Determining the period of oscillation
𝑇=
1
𝑓0
=
1
𝑆
108
=
10−8
𝑆 or 10 𝑛S
𝑇𝑂𝑁 = 0.69(𝑅1 + 𝑅2 )𝐶
∴ 𝑅1 =
𝑇𝑂𝑁
0.69𝐶
− 𝑅2 =
7.5𝑋10−6
0.69𝑋10−9
− 3.623188 𝛺 ≈ 7.2 𝛺
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
Assignment
16
EEE244
LECTURE 4
List twenty applications of
oscillators and multivibrators in
computer engineering.
Send your answer to
suraju.fadare@federalpolyilaro.edu.ng
after module 3 lecture 5 class is held
but before the next class (module 4
lecture 6 class).
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO
END OF
EEE244
LECTURE 4
EEE244
LECTURE 4
17
CONTACTS DETAILS FOR ANY QUESTION OR CLARIFICATION:
WHATSAPP: 08050555549
EMAILS: suraju.fadare@federalpolyilaro.edu.ng & asfadare@gmail.com
EEE244: ELECTRONICS III ; NEEII & PEEII ; FEDERAL POLYTECHNIC, ILARO, OGUN STATE, NIGERIA ; ENGR. S. A. FADARE & ENGR. B. A. OJO