Recommended Texts:
Fundamentals of Analog Circuits by Thomas L. Floyd and David Buchla, Prentice Hall, 2nd
Ed. (ISBN 0-13-060619-7)
The Essence of Analog Electronics by Colin Lunn, Prentice Hall (ISBN 0-13-360223-0)
Additional Reference Texts:
Analogue and Digital Electronics (a first course) by Peter H. Beards, Prentice Hall, 2nd Ed
1991. (ISBN 0-13-032962-2 hardback 0-13-032889-8 paperback)
Electronics: A Systems Approach by Neil Storey, Addison-Wesley, 2nd Ed. 1998.
(ISBN 0-201-17796-X)
Operational Amplifiers and Linear Integrated Circuits: Theory and Application by James M.
Fiore, West Publishing Co. 1992. (ISBN 0-314-90893-5)
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
1
Introduction
Electronic circuits are used in the manufacture of nearly all consumer products and electronic
technicians are employed in industry to design, maintain, and troubleshoot a large variety of
sophisticated electronic systems. Electronics covers a wide area of applications, such as the
control of industrial processes, sound (audio) amplification, computers and the internet,
telephone systems, radar systems, microwave systems, optoelectronic systems, motor and
generator systems, television, radio, satellite and fibre optic data transmitters and receivers, to
name but a few.
The Electronic Systems modules take a systems approach, i.e. the circuit is viewed as a
“black-box” and the behaviour of the system is studied. An introduction to some of the
components and circuitry that make up electronic systems is covered in the Electric Circuits
and Devices modules.
2
Analogue versus Digital
Electronic systems can be divided into two broad categories, digital and analogue (Note that
the American spelling is analog), however most electronic systems require both.
Analogue systems operate with values that vary continuously and have no abrupt transitions
between levels. Digital systems operate with discrete values.
Analogue Waveform
Digital Waveform
1 0 1 0 1 000 1 0 1 1 10 1
Since most physical quantities vary continuously (such as sound, position, velocity and
temperature) analogue waveforms represent these quantities more realistically. However, the
critical advantage of digital systems is that the data can be processed and transmitted more
efficiently and reliably than with analogue systems. Also, digital signals can be stored and
duplicated without degradation as, for example, on compact disc.
Prior to digital technology, electronic transmission (such as broadcast and telephone) was
limited to analogue technology. Digital technology is primarily used with new
communications media, such as satellite and fibre optic transmission. In order to access the
Internet, a modem is used to convert the digital information in your computer to analogue
signals for your phone line and to convert analogue phone signals to digital information for
your computer.
Digital waveforms generally have two possible states, as shown in the diagram above. These
states are most commonly represented by two voltage levels, a HIGH and a LOW. The states
are also commonly referred to as 1 and 0 or ON and OFF or TRUE and FALSE.
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ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
For a long time, almost all electronic systems were analogue, as most things we measure in
nature are analogue. For example, your voice is analogue, it contains an infinite number of
levels and frequencies. Therefore, if you wanted a circuit to amplify your voice, an analogue
circuit seems a likely choice.
However, demands in the telecommunications and the computer industry have led to a focus
on digital electronics. For example, telephone exchange systems need circuits and devices
that can make logical decisions based on certain input conditions. They need to be reliable
circuits that operate the same way every time. Thus, today most analogue exchanges are now
replaced by digital systems that provide greater capacity of data transfer and increased
reliability and security.
However, digital systems are not always the best option for a given application and in most
electronic systems a combination of both analogue and digital circuits are required.
2.1 Example of an analogue electronic system
A public address system
Original
sound
waves
Speaker
Reproduced
sound waves
Linear amplifier
Audio signal
Amplified audio signal
The original sound waves, which are analogue in nature are picked up by the microphone and
converted to a small analogue voltage called an audio signal. This voltage varies
continuously as the volume and frequency of the sound changes and is applied to the input of
a linear amplifier. The output of the amplifier, which is an increased reproduction of the
input voltage, goes to the speaker(s). The speaker changes the amplified audio signal back to
sound waves that have a much greater volume than the original sound waves picked up by the
microphone.
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ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
2.2 Example of a system with both analogue and digital circuits
A CD player
CD Drive
Speaker
01001011010
Digital to analogue
converter
Digital Data
Sound
waves
Linear amplifier
Analogue
reproduction
of music
audio signal
Amplified audio signal
The music is stored in digital form on the compact disk. A laser diode optical system picks
up the digital data from the rotating disk and transfers it to a digital to analogue converter
(DAC). The DAC changes the digital data into an analogue signal that is an electrical
reproduction of the original music. This signal is amplified and sent to the speaker(s) or
earphones for you to listen to. When the music was originally recorded on CD, a process
essentially the reverse of the one described here, using an analogue-to-digital converter
(ADC), was employed.
2.3
Summary of examples of analogue circuits
ADDERS:
AMPLIFIERS:
These are used to add
signals together
Increase signals
ATTENUATORS: Decrease signals
CLIPPERS:
COMPARATORS
:
CONVERTERS:
DETECTORS:
Prevent signals from
exceeding some set
amplitude limits
Compares a signal
against a reference,
usually a voltage
Changes a signal from
one form to another, for
example voltage-tofrequency converters
Remove information
from a signal, for
example a radio detector
removes voice or music
from a radio signal
DIVIDERS:
Performs arithmetic division
of a signal
FILTERS:
Removes unwanted
frequencies from a signal
MULTIPLIERS: Performs arithmetic
multiplication of some signal
characteristic, for example,
amplitude multiplier
OSCILLATORS: Change direct current to
alternating current
RECTIFIERS:
Change alternating current to
direct current
REGULATORS:
Hold some value, such a
voltage or current, constant
SWITCHES:
Turn signals on and off or
change the routing of signals
through an electronic
system.
4
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
3
Linearity
Analogue systems perform certain operations. These operations are usually performed on
signals where signals are electrical quantities, such as voltages or currents. For example, a
microphone converts a human voice into a small voltage whose frequency and level change
with time.
The term Linear Electronics is usually used in the electronics industry when referring to
analogue electronics. In a linear circuit the output is proportional to the input. For example,
a resistor is a linear component in which an increase in current is proportional to the applied
voltage as given by Ohm’s law. In general, a plot that shows the relationship between two
variable properties of a device defines a characteristic curve. For most electronic devices, a
characteristic curve refers to a plot of the current, I, plotted as a function of the voltage, V.
For example, a resistor has an IV characteristic described by a straight line, as shown in
below.
I (mA)
10
R
1
9
8
7
6
5
4
3
2
1
V (V)
1 2 3 4 5 6 7 8 9
Example of IV characteristic curve for a resistor
However, it should be noted that analogue electronic systems may also be non-linear systems.
For example, the diode has a characteristic curve for which the current is not proportional to
the voltage.
I (mA)
10
9
8
7
6
5
4
3
2
1
V (V)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Example of IV characteristic curve for a diode
5
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
4
Periodic Signals
A periodic signal repeats at a regular interval in time, for example, the sinusoidal waveform
shown below. The period (T) represents the time for a periodic wave to complete one cycle.
One cycle is the complete sequence of values that a waveform exhibits before another
identical pattern occurs. The period can be measured between any two corresponding points
on successive cycles.
Periodic waveforms are used extensively in electronics. Many practical electronic circuits
such as oscillators generate periodic waves. Most oscillators are designed to produce a
particular shaped waveform, either a sinusoidal waveform or non-sinusoidal waves such as
square, rectangular, triangle and sawtooth waves.
The most basic and important periodic waveform is the sinusoidal wave. Both the
trigonmetric sine and cosine functions have the shape of a sinusoidal wave. The term sine
wave implies the sine function, whereas the term sinusoidal wave means a waveform with the
shape of a sine wave. A sinusoidal waveform is generated as the natural waveform from
many ac generators and in radio waves. Sinusoidal waveforms are also present in physical
phenomena from generation of laser light, the vibration of a tuning fork, or the motion of
ocean waves.
y(t) = A sin ( t   )
y(t)
Period, T
Amplitude, A
t
Sinusoidal Waveform is a periodic signal
A sinusoidal curve may be expressed mathematically as:
y(t) = A sin (t  )
y(t)
vertical displacement of curve from horizontal axis as a function of time
A
amplitude is the maximum displacement from the horizontal axis

angular frequency in radians per second
t
time in seconds to a point on the curve

phase angle in radians is simply a fraction of a cycle that a waveform is shifted from a
reference waveform of the same frequency. It is positive if the waveform begins before t=0
and is negative if the curve starts after t=0.
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ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
y(t)
Period, T
Amplitude, A
t
y(t)
Period, T
Amplitude, A
t
Examples of Non-sinusoidal Periodic Waveforms
5
Frequency
Frequency is the number of cycle per second, where one complete cycle is 2 radians. Thus
dividing the angular frequency () by the number of radians in one cycle (2) gives the
frequency in hertz.

f 
2
where:
f
frequency in hertz (i.e. number of cycles per second)
angular frequency in radians per second

number of radians per cycle
2
The time in seconds for one cycle is the period, T. Thus the frequency in hertz is the
reciprocal of the period.
1
f 
T
For example, if a signal repeats every 1 ms, then its period is 1 ms and its frequency is
1
1
f  
 1  10 3  1kHz
3
T 1  10
7
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
6
Amplitude of Sinusoidal Wave
The amplitude of a sinusoidal wave is the maximum displacement from the horizontal axis.
For a voltage signal, the amplitude is called the peak voltage (Vp). When making voltage
measurements with an oscilloscope, it is easier to measure the peak-to-peak voltage (Vpp).
The peak-to-peak voltage is twice the peak value.
V(t) = Vpsin ( t   )
Voltage, V(t)
+Vp
Peak Voltage, Vp
Peak-to-Peak Voltage, Vpp
t
-Vp
6.1 Peak Voltage (Vp)
Average Value of Sinusoidal Wave
During one complete cycle, a sinusoidal waveform has equal positive and negative
excursions. Therefore, the mathematical definition of the average value of a sinusoidal
waveform must be zero. However, the term average value is generally used to mean the
average over a cycle without regard to sign. That is, the average is computed by converting
all negative values to positive and then averaging. Thus
Vavg 
2VP

 0.637VP
6.2 Effective Value (rms Value) of Sinusoidal Wave
In order to compare ac and dc voltages and currents, ac voltages and currents are defined in
terms of equivalent heating value of dc. This equivalent heating value is computed with
calculus and the result is called the rms (root-mean-square) voltage or current.
The rms voltage is related to the peak voltage by the following equation.
Vrms  0.707VP
8
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
7
Exercises
7.1 Exercise 1
An oscilloscope shows a wave repeating every 27 s. What is the frequency of the wave?
7.2 Exercise 2
A Digital Multi-Meter (DMM) indicates the rms value of a sinusoidal wave. If the DMM
indicates a sinusoidal wave is 3.5 V, what peak-to-peak voltage would you expect to observe
on an oscilloscope?
7.3 Exercise 3
A voltage waveform is described by the following equation:
V(t) = 20 sin(500 t)
(i)
(ii)
(iii)
(iv)
Determine the peak voltage and the average voltage.
Find the instantaneous voltage at time = 10 ms
Determine the rms voltage.
Find the frequency in hertz and the period of the waveform
7.4 Exercise 4
A voltage waveform is described by the following equation:
V(t) = 100 sin(200t + 0.52)
(i)
(ii)
(iii)
(iv)
Determine the peak voltage and the average voltage.
Find the instantaneous voltage at time = 2 ms
Determine the rms voltage.
Find the frequency in hertz and the period of the waveform
9
ELEK1289 - Electronic systems and practice II - Unit 1 – Introduction to Analogue
8
Analogue System – Black Box Approach
When analysing a complex electronic system, it is usual to break it down into a number of
functional blocks. It is usual to model an analogue system using block diagrams.
A block diagram shows all the individual functions of a system and how the signals flow
through the systems. This is used for system level test and debug.
A schematic diagram shows all the individual parts of the circuit and how they are
interconnected. This is required for component-level troubleshooting.
Troubleshooting begins at system level, where the technician observes symptoms and makes
measurements to determine which function or functions are faulty. This may lead to an entire
module, panel or circuit board being replaced. Component level debug usually takes longer
than system-level debug, so it may be more economical to replace an entire module or circuit
board.
Open Loop System
Input
Signal
Input
Electronic
Function
Output
Signal
Output
Power Supply
Open Loop System
Closed Loop System
FEEDBACK
information feed back
from output to input
Input
Signal
Input
Electronic
Function
Output
Signal
Power Supply
Closed Loop System
10
Output