Digital Elecronics and Microprocessor
PCC-EC202
By
Dr. Usha Ramdas Kamble,
Associate Professor and
Head Dept. of E&TC ,
SGGSIE&T,Nanded
1
COURSE PLAN
• Number Systems and Codes 03
• Boolean Algebra and Logic Gates- 03
• Simplification of Boolean Functions- 02
• Combinational Logic Design 08
• Sequential Logic Design 08
• Counters and Shift Registers08
• Semiconductor Memories –
06
• Introduction to VHDL/Verilog02
Total hours-40
Analog vs. Digital Signals
The information carrying signals
Analog Signal – Why Analog?
Example:
Telephone voice signal is analog
Digital Signals
Why Digital?
• Consist of pulses or digits with discrete levels or values .
• ExPhotoelectric cell output.
Coded light output.-Fiber optics
Analog and Digital waveforms
Advantages of digital over analog
• 1 -Ex- Analog meter Vs digital meter
• 2 -Ex- Analog clock Vs Digital clock
• 3 -EX-Analog audio Vs Digital audio
• A-Digital systems are easier to design
• B-Information storage is easy
• C-Accuracy is greater
• D-operation can be programmed
• E-Less affected by noise
• F -More digital circuitry can be fabricated on IC chips
Integrated Circuit
• SSI --- <12 gates- ex-Flip Flops
• MSI --- 12 to 99- ex-encoders,decoders
• LSI --- 100 to 9999- small memories and small microprocessors
• VLSI --- 10,000 to 99,999-Large memories and large microprocessors
• ULSI---- 100,000
9
10
Digital ICS
• Bipolar ICs
• Unipolar ICs
Information representation
• Bit- single
• Byte-8 bits
• Word• Nibble-4 bits
• Half word
• Double word
Logic
Positive Logic
Negative Logic
New Symbol
•To distinguish between positive and negative logic
Negative logic NAND
(positive logic NOR)
Motivation
• Applications
• Extension of the COURSE
• VHDL-Is an acronym for VHSIC
(Very High Speed Integrated Circuit
Hardware Description Language )
Course Objectives
To acquaint students with
•1. Digital codes and Boolean Algebra used in digital design.
•2. Real time problem implementation using Boolean functions.
•3. Combinational and sequential logic design and basic digital design
building block.
16
Content of course
•Digital Codes, Boolean Algebra and Logic Families:
BCD codes , binary codes , error detecting and
correcting codes, reflective properties of codes,
Unit distance codes, Theorems and properties of
Boolean algebra, Boolean functions, Canonicals and
standard forms, Other logic operations, Digital logic
gates, Digital IC logic families, Logic design
examples.
17
• Simplification of Boolean Functions: The K-map method: 2, 3, and 4
variable maps, five and six variable maps, Quine McCluskey method
of simplification and NAND-NOR realization.
18
• Combinational Logic Design: Adders, Subtractors, Code converters,
Binary parallel adders, Decimal adders, Magnitude comparators,
Multiplexers, Demultiplexers, Decoders and Encoders, Signed
magnitude numbers and their arithmetic implementation.
19
• Sequential Logic Design: Flip-flops: J-K, D, T, SR flip-flops, Excitation
tables of flip-flops, Conversion of flip flops, Design of Flip Flops,
Applications of Flip Flops.
20
• Counters and Shift Registers: Asynchronous counters, Synchronous
counters, mod-3Counters, mod-5 counters, presettable counters,
shift-counters, Up-down counters, Ripple counters, Shift registers,
Serial in serial out, Serial in parallel out, Parallel in serial out, and
Parallel in parallel out shift registers, Introduction to VHDL/Verilog.
21
• Microprocessors: What is Microprocessor? Princeton and Harvard
Architecture, Overview of 8085 Microprocessor Architecture, Pin
Description of 8085 microprocessor, Survey of 4/8/16/32 bit
Microprocessors, Applications of microprocessors.
22
• Semiconductor Memories: Memory organization and operation,
expanding memory size, classification and characteristics of
memories, sequential memories, Read only memories, R/W
memories, content addressable memories, CCD memories.
23
Course Outcomes (COs):
• Upon successful completion of this course, the student will be able
to:
• Understand fundamentals concepts used in digital circuits.
• Able to solve examples of any number system such as trinary,
quinary etc and study of digital codes and Boolean algebra.
• Able to Design code converter circuits such as binary to gray, Gray
to binary, BCD to exess-3 and excess-3 to BCD etc..
• Able to understand and design combinational circuits such as (i)
Multiplexers, Demultiplexers using Gates and ICS.(ii) encoders and
decoders (iii) Parity generators (iv) Adders and subtractors (v)
Logical design problems
• Able to understand and design of sequential circuits such as flip
flops, counters and registers etc.
• Acquire fundamental knowledge of memories such as RAM, ROM,
EPROM etc.
24
Text/Reference Books:
1. M. Morris Mano, Digital Logic and Computer Design, PHI
Publication, New Delhi.
2. William I. Fletcher, An Engineering approach to Digital Design,
PHI Publication, New Delhi.
3. Malvino and D. Leach, Digital Principles and Application, Mc
Graw Hill Book Company.
4. R. P. Jain, Modern Digital Electronics, McGraw Hill Book
Company.
5. Louis Nashelsky, Introduction to Digital Technology, John
Wiley & Sons.
6. Williams H. Gothman, Digital Electronics, PHI Publication, New
Delhi.
25
Course Outcomes
•At the end of this course students will demonstrate the
ability to
•1. Digital codes and their applications, code conversions,
Boolean functions implementation and simplification, Logic
families.
•2. Combinational logic circuits, Implementation of logical
functions using MUX, DEMUX, Decoders and encoders.
•3. Sequential logic circuits such as flip flops, counters and
registers, Design of sequential logic circuits.
•4. Implementation of small digital application
•5. Microprocessors and semiconductor memories.
26
Analog vs digital :
Analog and digital signals are used to transmit
information, usually through electric signals. In both
these technologies, the information, such as any audio
or video, is transformed into electric signals.
The difference between analog and
digital technologies is that –
In analog technology, information is translated into
electric pulses of varying amplitude.
In digital technology, translation of information is into
binary format (zero or one) where each bit is
representative of two distinct amplitudes.
27
Analog Vs Digital
Representat
ion
Example
Waves
Analog signal is a continuous
signal which represents
physical measurements.
Digital signals are discrete
time signals generated by
digital modulation.
Uses continuous range of
values to
represent information
Uses discrete or
discontinuous values to
represent information
Human voice in air, analog
electronic devices.
Computers, CDs, DVDs,
and other digital electronic
devices
Denoted by sine waves
Denoted by square waves
28
Analog Vs Digital
Analog technology records
Technology waveforms as they are.
Samples analog waveforms into a
limited set of numbers and records
them.
Subjected to deterioration by noise
Data during transmission and write/read
transmission cycle.
s
Can be noise-immune without
deterioration during transmission and
write/read cycle.
More likely to get affected reducing
Response to accuracy
Noise
Less affected since noise response are
analog in nature
Analog hardware is not flexible.
Digital hardware is flexible in
implementation.
flexibility
Can be used in analog devices only.
Uses Best suited for audio and video
transmission.
Best suited for Computing and digital
electronics.
29
Analog Vs Digital
pplications Thermometer
PCs, PDAs
Analog signal processing can be
done in real time and consumes
Bandwidth less bandwidth.
There is no guarantee that digital signal
processing can be done in real time and
consumes more bandwidth to carry out
the same information.
Memory
Stored in the form of wave signal
Stored in the form of binary bit
Analog instruments usually have a
scale which is cramped at lower
Errors end and give considerable
observational errors.
Digital instruments are free from
observational errors like parallax and
approximation errors.
Analog instrument draws large
Power power
Digital instrument drawS only negligible
power
Low cost and portable
Cost is high and not easily portable
Cost
30
Positive and Negative Logic
•The same physical gate has different logical meanings depending
on interpretation of the signal levels.
•Positive Logic
•HIGH (more positive) signal levels represent Logic 1
•LOW (less positive) signal levels represent Logic 0
•Negative Logic
•LOW (more negative) signal levels represent Logic 1
•HIGH (less negative) signal levels represent Logic 0
•A gate that implements a Positive Logic AND function will
implement a Negative Logic OR function, and vice-versa.
Positive and Negative Logic
•Given this signal level table:
Inpu
tX Y
L L
L H
H L
H H
•What logic function is implemented?
Positiv (H =
Logi
(L =
e
1)
c 0
0) 0
0
1
1
1
1
1
0
Negativ
Logi
e
c 1
1
0
0
1
(H =
(L =
0)
1) 1
0
0
0
Outpu
t
L
H
H
H
Positive and Negative Logic (continued)
• Rearranging the negative logic terms to the standard function table
order:
Positiv (H =
Logi
(L =
e
1)
c 0
0) 0
0
0
1
1
1
1
0
1
1
1
OR
Negativ (H =
Logi
(L =
e
0)
c 0
1) 0
0
0
0
1
1
0
0
1
1
1
AND
Logic Symbol Conventions
•Use of polarity indicator to represent use of negative
logic convention on gate inputs or outputs
X
Y
X
Y
Positive
Logic
Z
CK
T
Logic
Circuit
XY Z
Z
X
Y
Z
Negative
Logic
LL
LH
HL
HH
L
H
H
H
Digital Logic
• Digital logic is the representation of signals and sequences of a digital
circuit through numbers.
• It is the basis for digital computing and provides a fundamental
understanding on how circuits and hardware communicate within a
computer.
35
Logic Gate
• A Digital Logic Gate is an electronic device that makes logical
decisions based on the different combinations of digital signals
present on its inputs.
• Digital logic gates may have more than one input but generally only
have one digital output.
36
Logic
• a particular mode of reasoning viewed as valid or faulty
37
Graduate Aptitude Test in
Engineering
Syllabus
38
Linear Algebra: Matrix Algebra, Systems of linear
equations,
Eigen
values
andeigenvectors.
Calculus: Mean value theorems, Theorems of
integral calculus, Evaluation of definite and
improper integrals, Partial Derivatives, Maxima
and minima, Multiple integrals, Fourier series.
Vector identities, Directional derivatives, Line,
Surface and Volume integrals, Stokes, Gauss and
Green's theorems
39
Differential equations: First order equation (linear and
nonlinear), Higher order linear differential equations
with constant coefficients, Method of variation of
parameters, Cauchy's and Euler's equations, Initial and
boundary value problems, Partial Differential Equations
and
variable
separable
method.
Complex variables: Analytic functions, Cauchy's integral
theorem and integral formula, Taylor's and Laurent'
series,
Residue
theorem,
solution
integrals.
40
Probability
and
Statistics: Sampling
theorems,
Conditional probability, Mean, median, mode and
standard deviation, Random variables, Discrete and
continuous distributions, Poisson, Normal and Binomial
distribution, Correlation and regression analysis.
Numerical Methods: Solutions of non-linear algebraic
equations, single and multi-step methods for differential
equations.
Transform
Theory: Fourier
transform,Z-transform.
transform,
Laplace
41
• GENERAL APTITUDE(GA):
•Verbal Ability: English grammar, sentence completion,
verbal analogies, word groups, instructions, critical
reasoning and verbal deduction.
42
Electronics
and
Communication
EngineeringNetworks: Network
graphs:
matrices
associated with graphs; incidence, fundamental cut set
and fundamental circuit matrices. Solution methods:
nodal and mesh analysis. Network theorems:
superposition, Thevenin and Norton's maximum power
transfer, Wye-Delta transformation. Steady state
sinusoidal analysis using phasors. Linear constant
coefficient differential equations; time domain analysis of
simple RLC circuits, Solution of network equations using
Laplace transform: frequency domain analysis of RLC
circuits. 2-port network parameters: driving point and
transfer functions. State equations for networks
43
•Electronic Devices: Energy bands in silicon, intrinsic
and extrinsic silicon. Carrier transport in silicon:
diffusion current, drift current, mobility, and
resistivity. Generation and recombination of carriers.
p-n junction diode, Zener diode, tunnel diode, BJT,
JFET, MOS capacitor, MOSFET, LED, p-I-n and
avalanche photo diode, Basics of LASERs. Device
technology: integrated circuits fabrication process,
oxidation,
diffusion,
ion
implantation,
photolithography, n-tub, p-tub and twin-tub CMOS
process.
44
Analog Circuits: Small Signal Equivalent circuits of
diodes, BJTs, MOSFETs and analog CMOS. Simple diode
circuits, clipping, clamping, rectifier. Biasing and bias
stability of transistor and FET amplifiers. Amplifiers:
single-and multi-stage, differential and operational,
feedback, and power. Frequency response of
amplifiers. Simple op-amp circuits. Filters. Sinusoidal
oscillators; criterion for oscillation; single-transistor
and op-amp configurations. Function generators and
wave-shaping circuits, 555 Timers. Power supplies.
45
• Digital circuits: Boolean algebra, minimization of Boolean functions;
logic GATEs; digital IC families (DTL, TTL, ECL, MOS, CMOS).
Combinatorial circuits: arithmetic circuits, code converters, multiplexers,
decoders, PROMs and PLAs. Sequential circuits: latches and flip-flops,
counters and shift-registers. Sample and hold circuits, ADCs, DACs.
Semiconductor memories. Microprocessor(8085): architecture,
programming, memory and I/O interfacing.
46
• Signals and Systems: Definitions and properties of Laplace transform,
continuous-time and discrete-time Fourier series, continuous-time and
discrete-time Fourier Transform, DFT and FFT, z-transform. Sampling
theorem. Linear Time-Invariant (LTI) Systems: definitions and properties;
causality, stability, impulse response, convolution, poles and zeros,
parallel and cascade structure, frequency response, group delay, phase
delay. Signal transmission through LTI systems.
47
•Control Systems: Basic control system components;
block diagrammatic description, reduction of block
diagrams. Open loop and closed loop (feedback) systems
and stability analysis of these systems. Signal flow graphs
and their use in determining transfer functions of
systems; transient and steady state analysis of LTI
control systems and frequency response. Tools and
techniques for LTI control system analysis: root loci,
Routh-Hurwitz criterion, Bode and Nyquist plots. Control
system compensators: elements of lead and lag
compensation, elements of
Proportional-Integral-Derivative (PID) control. State
variable representation and solution of state equation of
LTI control systems.
48
•Communications: Random signals and noise: probability, random
variables, probability density function, autocorrelation, power
spectral density. Analog communication systems: amplitude and
angle modulation and demodulation systems, spectral analysis of
these operations, superheterodyne receivers; elements of
hardware, realizations of analog communication systems;
signal-to-noise ratio (SNR) calculations for amplitude modulation
(AM) and frequency modulation (FM) for low noise conditions.
Fundamentals of information theory and channel capacity theorem.
Digital communication systems: pulse code modulation (PCM),
differential pulse code modulation (DPCM), digital modulation
schemes: amplitude, phase and frequency shift keying schemes
(ASK, PSK, FSK), matched filter receivers, bandwidth consideration
and probability of error calculations for these schemes. Basics of
TDMA,
FDMA
and
CDMA
and
GSM.
49
•Electromagnetics: Elements of vector calculus: divergence and
curl; Gauss' and Stokes' theorems, Maxwell's equations:
differential and integral forms. Wave equation, Poynting
vector. Plane waves: propagation through various media;
reflection and refraction; phase and group velocity; skin depth.
Transmission lines: characteristic impedance; impedance
transformation; Smith chart; impedance matching; S
parameters, pulse excitation. Waveguides: modes in
rectangular waveguides; boundary conditions; cut-off
frequencies; dispersion relations. Basics of propagation in
dielectric waveguide and optical fibers. Basics of Antennas:
Dipole antennas; radiation pattern; antenna gain.
50
IES : Indian Engineering Services
•Digital Electronic Circuits – Digital electronics circuits
correspond to signals by distinct bands of analog level. All
levels inside a band symbolize the identical signal status.
This includes Transistor as a switching element;
Simplification of Boolean functions, Karnaguh map , Boolean
algebra, and applications; IC logic families : DTL, ECL, TTL,
NMOS, CMOS and PMOS gates and their comparison; Full
adder , Half adder; IC Logic gates and their characteristics;
Digital comparator; Multiplexer Demulti-plexer; Flip flops.
J-K, R-S, T and D flip-flops; Combinational logic Circuits;
Different types of registers and counters Waveform
generators. Semiconductor memories.A/D and D/A
converters. ROM an their applications.
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
Objectives
• Describe the characteristics of an analog signal.
• Describe the characteristics of a digital signal.
• Explain the benefits of converting an analog voice signal into a digital
signal.
• Explain how analog signals are connected from a transmitter to a
receiver.
94
Objectives (continued)
• Explain how digital signals are coupled from a coder to a decoder.
• Explain what Alternate Mark Inversion (AMI) is.
• Explain what Manchester coding is.
• Explain what differential Manchester coding is.
95
Objectives (continued)
• Explain Non-Return to Zero Level (NRZ-L) and Non-Return to Zero
Invert (NRI) signaling.
• Explain the correlation between bandwidth and power loss over the
local loop.
96
7.1 Communication Signals and Protocols
•A communication protocol in telecommunications will
specify:
• What type of signal is to be used for communication.
• How the signal is to be manipulated.
• How the signal is to be placed on the transmission facility.
•An analog signal is an electrical signal with continuously
varying amplitude.
•A digital signal is a signal that can assume one of several
discrete states.
97
Sine Waves
98
Voice Signal Composed of Many Sine Waves
99
Digital Signal
100
7.2 Analog Signal
•All electrical signals with varying amplitudes are
called analog signals (analog is short for
“analogous”).
•The transceiver was a device that contained a coil
of wire suspended inside a magnet.
•The limitations of the transceiver were overcome
by the development of the carbon granule
transmitter.
•Devices that convert a signal from one form of
energy to another are called transducers.
101
Conversion of Airwaves into Electrical Waves
102
Electrical Power to the Transmitter
103
Telephone Receiver and Hybrid Network
104
7.3 Connecting the Telephone to the Central
Exchange
• The telephones at our residences and any small businesses connect
via one pair of wires to a switching system called the local central
office.
• Since the switching system is located at the center of the hub, it is
called the central office, central exchange, or central.
• The pair of wires that connects the telephone to the central
exchange is called the local loop.
105
Central Office Exchange Territory
106
Main Distributing Frame (MDF)
107
Cables from Main Distributing Frame to Line
Equipment
108
Telephone Circuit
109
7.4 Analog Signal in the Local Loop
•The telephone receives its power from the central exchange
via the line circuit in the exchange.
•When a telephone is taken off hook, electric current will
flow.
•The transmitter of a telephone and the electronic chip that
provides the tones for a touchtone dial require about 8 V to
function properly.
•A varistor in the circuit limits current flow to a maximum of
60 mA because a current of more than 60 mA contributes to
the possibility of crosstalk.
110
Varistor of Telephone
111
Twisted-Pair Wire
• Twisting the wires that serve one telephone around each other
eliminates crosstalk.
• The tighter the twist, the higher-frequency signal it can carry.
• Data grade (CAT-5) cable has many more twists per inch than voice
grade (CAT-3) cable.
112
7.5 Coupling Analog Signals from One Circuit
to Another
• Transformers
• Capacitor Coupling
• Silicon Controlled Rectifiers (SCRs)
113
Coupling Analog Signals from One Circuit to
Another
•When the transmitter of the telephone converts a voice
signal into an analog electrical signal, the analog signal is a
continuously varying electrical signal.
•The analog signal is a continuously varying dc signal.
• Current flows in one direction only.
• The signal looks like an ac signal that has a center point of 40 mA.
•We can use transformers or capacitors to couple voice
signals from one circuit to another while isolating the dc
voltages of these circuits from each other.
114
Voice Signal in the Local Loop
115
Transformers Used to Couple Voice Signals
•The 40 mA of current through the primary winding sets
up a magnetic field of a certain strength.
•When the local loop transports an analog electrical
voice signal to the primary winding of the transformer,
the analog signal causes the magnetic field established
by the primary winding to vary.
•Variations in the magnetic field cause an analog signal
to be induced into the secondary winding and into the
circuit connected to the secondary winding.
116
Transformers Used to Couple Voice Signals
117
Capacitor Coupling Voice Signals
• In the capacitor-coupled circuit, the 40 mA of current in the local
loop causes the capacitor to charge to a certain value.
• When the local loop circuit transports an analog electrical voice
signal, the analog signal causes the electric charge on the capacitor
to vary in unison with the changes of the analog signal.
• This changing charge on the capacitor is coupled to the next circuit.
118
Capacitor Coupling Voice Signals
119
Strowger Connector Switch
120
Silicon Controlled Rectifiers
•Today, we do not use either transformer or
inductive-capacitive battery feed circuits for coupling
voice signals.
•The line circuit that interfaces a local loop to the central
exchange includes a codec chip and a hybrid network in
the circuit.
• The codec chip converts all analog signals received from the
local loop to digital signals.
• Since the analog voice signal is converted into a digital signal,
we cannot use the same techniques to couple the signal from
one circuit to another.
121
Silicon Controlled Rectifiers
•The technique used to couple digital signals from one
circuit to another is to gate them using silicon controlled
rectifiers (SCRs).
•Electronic gates are placed between two circuits and
are turned on when we wish to connect signals from
one circuit to another.
• Voice signals at the telephone are converted into analog
electrical signals at the telephone.
• Analog electrical signals are converted to digital signals at the
central exchange.
• Digital signals are connected via the PSTN switching network to
a receiver for decoding.
122
Coupling Voice Signals via Codecs
123
7.6 Conversion of Voice into Digital Signals
•The standard used in the PSTN to convert analog voice
signals into digital signals is pulse code modulation (PCM).
•Other processes are available:
• Adaptive Differential Pulse Code Modulation (ADPCM)
• Predictive Pulse Code Modulation
•Digital voice signals are connected from one point to
another by connecting the coder portion of one codec via a
transmission medium to the decoder portion of another
codec.
124
7.7 Conversion of the PSTN into a Digital
Network
•Using digital signals to represent voice or data is much
more efficient than using analog signals.
•Analog signals can be carried only so far by a
transmission medium before the signal gets so weak
that it must be amplified. This introduces more noise
into the signal.
•Digital signal regenerators strip all noise out of a signal
by regenerating crisp, clean, new 1s and 0s.
•Although the circuitry between central exchanges is
almost 100% digital, the circuitry that connects our
telephone to the central exchange is mostly analog.
125
Effects of Noise
126
7.8 Digital Data over the Local Loop
• Integrated Services Digital Network (ISDN)
• Asymmetrical Digital Subscriber Line (ADSL)
127
Integrated Services Digital Network (ISDN)
•Provides the ability to place digital data directly into
the ISDN equipment on each end of the circuit.
•Uses twisted-pair copper wire to connect
equipment on the customer’s premises to the local
exchange.
• ISDN lines do not connect to regular line circuits at the central
exchange; they connect to special line interface circuits called
ISDN line circuits.
• If an ISDN line is to be used for the transmission of a voice
signal, The ISDN terminal equipment on the customer’s
premises contains a codec, which converts the analog signal
into a 64,000 bps digital signal.
128
Asymmetrical Digital Subscriber Line (ADSL)
•This service is classified as a digital service, but in fact
uses a modem, and the digital data on the customer’s
premises will be used to modulate an analog signal
transmitted to the central exchange.
• Like ISDN, this ASDL service cannot be interfaced to the
exchange using a regular line circuit.
• ASDL lines are connected at the central exchange to another
ASDL modem.
• The ASDL modem in a central exchange is part of a device
called a Digital Subscriber Line Access Multiplexer (DSLAM).
•ADSL uses high-frequency analog signals, which are
modulated by the digital data to be carried.
129
7.9 Digital Data Coding Techniques
•Alternate Mark Inversion (AMI)
•Non-Return to Zero – Level (NRZ-L)
•Non-Return to Zero – Invert (NRZ-I or NRI)
•Manchester
•Differential Manchester
130
Alternate Mark Inversion Signal
131
NRZ-L Signal
132
NRI Signal
133
Manchester Signal
134
Differential Manchester
135
7.10 Bandwidth vs. Power Loss
• Bandwidth describes the range of frequencies found within a band.
• The bandwidth of a signal determines the information carrying
capacity of the signal.
• When we wish to transfer information over the local-loop twisted
pair, we need high-frequency signals to transfer high data rates.
136
Bandwidth vs. Power Loss
•The higher the frequency transmitted, the greater the
power loss incurred due to:
• Distributed capacitance that exists between the two wires of
the local loop.
• The inductance in the wire itself.
•When a signal is carried by twisted-pair copper wire, it
is especially susceptible to interference (noise) from
signals in adjacent wire pairs.
•It is important to maintain a high signal-to-noise ratio
(SNR).
137
7.11 Summary
• Telecommunications requires a transmitter, medium, and receiver.
• To ensure accurate transmission and reception of signals:
• The transmitter and receiver must use the same protocols.
• Protocols specify the rules and procedures that must be followed to set up
and maintain accurate, reliable communication.
138
Summary
• The signals used in telecommunications are either analog or digital.
• An analog signal is a signal with continuously varying amplitude.
• A digital signal assumes one of a number of discrete voltage levels.
• The transmitter of a telephone creates analog electrical signals. The
local loop was designed to handle these signals efficiently.
139
Summary
• Almost all central exchanges used in the PSTN are digital switching
systems.
• The line interface to these switching systems contains a codec.
• Converts the analog voice signal into a 64,000 bps digital signal.
• Uses PCM
140
Summary
•The wider the bandwidth of an analog signal, the more
information it is capable of carrying in a given
timeframe.
•The use of high-bandwidth signals also makes the data
more susceptible to interference from noise.
• Higher-frequency signals are needed to provide wider
bandwidths.
• Higher-frequency signals encounter higher power losses when
transmitted over twisted-pair copper wire.
141