Engineering science

1. Chapter 4- Information and energy
control systems
4.1 Information systems
4.1.1 block diagram representation of a typical
information system (eg audio-communication,
instrumentation, process monitoring)
4.1.2 qualitative description of how electrical signals
convey system information
4.1.3 function, operation and interfacing of information
system components (eg transducers, transducer
output and accuracy, amplifier types, typical gain,
resolution of analogue to digital and digital to
analogue converters, types of oscillators and
operating frequencies)
4.1.4 effect of noise on a system
4.1.5 determination of system output for a given input

2.  Typical information systems
BS
Base Station (BS)
UE UE
UE
User Equipment (UE)

4. • Communication System
– The purpose of a Communication System is to
transport an information bearing signal from a source
to a user destination via a communication channel
Source Destination
• Source: -discrete events (from an alphabet)
-waveforms (speech, sound, images, video)
• Transmission media: -radio frequency ”on the air”
-satellite channel
-copper wire
-optical fiber

5. Block diagram representation of a
typical information system

6.  Transducer converts the output of a source into an electrical
signal.
 The heart of the communication system consists of three basic
parts,
 the transmitter
 the channel, and
 the receiver.
 The transmitter converts the electrical signal into a format that
is suitable for transmission - modulation.
 Example of modulation:
 amplitude modulation (AM),
 frequency modulation (FM).
 Receiver: The receiver performs carrier demodulation to
extract the message signal contained in the received signal

7. Amplitude and frequency modulation
• In AM broadcast, the information signal that is
transmitted is contained in the amplitude variations
of the sinusoidal carrier.
• In an FM broadcast, the information signal that is
transmitted is contained in the frequency variations
of the sinusoidal carrier.
• The choice of the type of modulation is based on
several factors, such as the amount of bandwidth
allocated, the types of noise and interference that
the signal encounters in transmission over the
channel, and the electronic devices that are
available for signal amplification prior to
transmission.

8. Pulse modulation techniques

9. Time division multiplexing

10. • Digital signals are easier to multiplex than
analog signals
• Multiplexing is the process of allowing
multiple signals to share the same
transmission channel.

11. • Examples of channels:
– Wireless channels: atmosphere (free
space)
– Telephone channels: wirelines, optical
fiber cables.
• Distortions of channels
– Additive noise - thermal noise
– Multipath propagation – fading

12. Analog vs digital communication
• Analog signal - continuous signal, e.g., speech signal.
• Analog signal can be transmitted directly via carrier
modulation over the communication channel and
demodulated at the receiver (Analog communications).
• An analog source can be converted into a digital form and
the digital form can be transmitted via digital modulation
and demodulated as a digital signal (Digital
communications).
• Advantages of digital communications
– Signal fidelity is better controlled.
– Regeneration of the digital signal can be performed without
noise enhancement.

13. Digital Communication Systems
Basic elements of digital communication system

14. • Digital Source, e.g., English text, computer data.
• Fundamental elements of digital communication systems
– Information source: analog or digital
– Source encoder: converts the information source to binary form and
removes the redundancy. (source encoding for data compression)
– Channel encoder: adds redundancy to overcome the effects of noise
and interference introduced by the channel.
– Digital modulator: maps the binary information sequence into signal
waveforms.
– Digital demodulator: convert the received waveform to binary
information sequence.
– Channel decoder: corrects the demodulated errors based on the
redundancy added by the channel encoder.
– Source decoder: recover the original information source.

15. Digital systems
• Advantages
– More resilient to interference and imperfections
– Can be mathematically processed allowing compression or
enhancement of data
– Information can be stored as numerical data: data storage cheap
– Longevity: data can be stored over very long periods of time.
• Disadvantage
– Digital signal will not be an exact copy of the original analogue
signal: sampling error
– Complex processing involved
– Takes time to do
– The transmitter and receiver have to be synchronized

16. Advantages of digital signals
• The most important advantage of digital
communications is noise immunity.
• Receiver circuitry can distinguish between a binary 0
and 1 with a significant amount of noise.
• Digital signals can be stripped of any noise in a
process called signal regeneration
1 0 1 1 0 1
Voltage (V)
Time (sec)
analog signal with noise digital signal with noise

17. Analog Digital
Amplified regenerated
Noise added no noise added
original analog signal original analog signal
signal at repeater 1 signal at repeater 1
signal at repeater 2 signal at repeater 2
signal at repeater 3 signal at repeater 3

18. Conversion from analog to digital
• Translating an analog signal into a digital
signal is called analog-to-digital (A/D)
conversion, digitizing a signal, or encoding.
– The device used to perform this translation is
known as an analog-to-digital converter or
ADC.

19. • An analog signal is a smooth or continuous
voltage or current variation.
– Through A/D conversion these continuously
variable signals are changed into a series of
binary numbers.
Voltage (V)
01101010100111001101010101111
Time (sec)

20. Step 1- sampling
• The first step in A/D conversion is a process
of sampling the analog signal at regular time
intervals.
sample points
Voltage (V)
sampling frequency
1
f =
T
Time (sec)
sampling period (T)

21. Sampling: Time-Domain Plot

22. • How often do we need to sample the signal?
– How large does our sampling frequency f need
to be in order to accurately represent the
signal?
o ae V
o ae V
Vt g ( )
Vt g ( )
l
l
T e sc
i
m( e ) T e sc
i
m( e )
high sampling rate
o ae V
o ae V
Vt g ( )
Vt g ( )
l
l
T e sc
i
m( e ) T e sc
i
m( e )
low sampling rate

23. Minimum sampling frequency
• The minimum sampling rate required in order
to accurately reconstruct the analog input is
given by the Nyquist sampling rate fN given
f N ≥ 2 fm
where fm is the highest frequency of the analog
input.
– The Nyquist rate is a theoretical minimum.
– In practice, sampling rates are typically 2.5 to 3
times the Nyquist rate fN.

24. Step 2-quantization
• The actual analog signal is smooth and continuous
and represents an infinite number of actual voltage
values.
– It is not possible to convert all analog samples to a
precise binary number.
– Therefore, samples are converted to a binary number
whose value is close to the actual sample value.
• The A/D converter can represent only a finite number
of voltage values over a specific range.
• An A/D converter divides a voltage range into discrete
increments, each of which is represented by a binary
number.

25. A/D conversion
• The process of mapping the sampled analog
voltage levels to these discrete, binary values is
called quantization.
• Quantizers are characterized by their number of
output levels.
• An N-bit quantizer has 2N levels and outputs binary
numbers of length N.
– Telephones use 8-bit encoding → 28 = 256 levels
– CD audio use 16-bit encoding → 216 = 65,536 levels

26. Quantization

27. Quantization: Illustration
2m p
∆v =
L

29. Transducers
Definition:
A transducer is a device, which converts one type of
physical property, quantity or condition into another easily
usable form
Advantages of transducers
If the output signal from the transducer is in electrical form
then it is convenient to handle and has many advantages.
– Ease of amplification
– Ease of integration and differentiation
– Ease of convertibility from analog to digital and vise versa
– Remote controllability and easy data transmission capability
– Compatibility with microprocessors and computers

30. Categorization of transducers
• Input (sensors) and output (actuators and
displays)
• Active (where external excitation source is
needed) and passive
• Analog (continuous in time domain) /digital
(discrete in time domain and may
quantized in amplitude) and carrier
• Primary and secondary

31. Input and output transducers
• Input Transducers convert a quantity to an electrical signal (voltage)
or to resistance (which can be converted to voltage). Input
transducers are also called sensors.
Examples:
– LDR converts brightness (of light) to resistance.
– Thermister converts temperature to resistance.
– Microphone converts sound to voltage.
• Output Transducers convert an electrical signal to another quantity
Output transducers can be either an actuator or a display
Examples:
– Lamp converts electricity to light.
– LED converts electricity to light.
– Loudspeaker converts electricity to sound.
– Motor converts electricity to motion.
– Heater converts electricity to heat

32. Signal conditioning
• Amplification
– To strengthen the signal
– Before transmission, repeater stations and before usage
• Level shifting
– To make bipolar signal to uni-polar signal
• Filtering
– To remove noise
– Limit bandwidth for sampling
• Linearising
– To convert nonlinear quantities into linearly varying quantities
– Eg: use of exponential amplifier if the transducer response is
logarithmic
• Isolation
– To amplify only the ac component of the electrical signal
– To avoid distortions of signals

33. Amplification
• Amplifier types
– By construction
• IC amplifiers (eg:-operational amplifiers)
• Transistor/FET amplifiers (VMOS)
• Valve amplifiers
– By application
• Pre-amplifier
• Power amplifier (eg:-push pull amplifiers)
• Intermediate stage amplifiers
• Low noise amplifiers

34. Noise rejection by filtering

35. Noise
• Any electrical signal transmitted from one point to another
point is classified as having two parts, the desirable part
and undesirable part, which is noise
• There are three types of noise:
(a) External noise
(b) Internal noise.
(c) Cross talk
• External Noise
External noise is noise that is generated outside the
device or circuit. Below are the primary sources of external
noise:
– Lightning
– Solar noise
– Cosmic Noise
– Man-made noise

36. • Internal Noise
Internal noise is caused by electrical interference generated within the
device or circuit. Below are the primary sources of internal noise:
– Shot noise
The name originates from the sound that it produces at the audio output of
a receiver. The sound is similar to that leaf shot falling on top of a tin roof.
This noise is caused by the random arrival of carriers (holes and electrons)
at the output element of electronic devices, such as diode and transistor.
– Thermal noise
It is caused by rapid and random movement of electrons within a conductor
due to thermal agitation. Since particles such as free electrons are in
movement, they posses kinetic energy that is directly related to the
temperature of the resistive body. Below is the equation shows the
mathematical relationship that was developed by Johnson

37. • Cross Talk
Many of us have experienced listening to other telephone
conversations. This type of noise called cross talk occurs as a
result of inductive and capacitive coupling from adjacent channels.
Subscriber loops and trunk circuits commonly multiplexed together
to form bundled cables often have severe cross talk, particularly in
long lengths of cable.
Noise measurements
Several mathematical tools have been developed to evaluate the
effects of noise based on its magnitude. There are two types of
measurements:
(a) Signal-to-Noise Ratio
The ratio of signal power to noise power.

38. (b) Noise Figure and Noise
– Noise factor is a measure of how noisy a device is. It
is the ratio of signal-to-noise power at the input
of a device to the signal-to-noise power at its
output. Expressed in decibels, noise factor is called
noise figure.