This document discusses signals and systems in 3 paragraphs: 1) Signals are variables that carry information and can be continuous or discrete functions of independent variables like time, space, etc. Examples given are electrical, biological, acoustic, and video signals. 2) Systems process input signals to produce output signals. Examples of systems include electrical circuits, aircraft/spacecraft dynamics, algorithms for data analysis. 3) Systems can be interconnected by cascading, providing feedback, or connecting in parallel to build more complex systems or modify their responses. Interconnections are represented using signal flow diagrams.

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HINDUSTHAN
INSTITUTE OF TECHNOLOGY
COIMBATORE
B.E. (ECE) – 2013 Regulations
Second B.E. (ECE) – III Semester
EC8352– Signals and Systems
UNIT-1
HAKKEM.B/ASSISTANT PROFESSOR/ECE

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1) Signals
Signals are variables that carry
information
2) Systems
Systems process input signals to
produce output signals.
Signals and Systems

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SIGNALS
Signals are functions of independent variables that carry
information. For example:
• Electrical signals --- voltages and currents in a circuit
• ECG--- Time is often the independent variable for signals. The
electrical activity of the heart recorded with electrodes on the
surface of the chest — the electrocardiogram (ECG or EKG).
• Acoustic signals --- audio or speech signals (analog or digital)
• Video signals --- intensity variations in an image (e.g. a CAT scan)
• Biological signals --- sequence of bases in a gene


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THE INDEPENDENT VARIABLES
• Can be continuous
— Trajectory of a space shuttle
— Mass density in a cross-section of a brain
• Can be discrete
— DNA base sequence
— Digital image pixels
• Can be 1-D, 2-D, ••• N-D
• For this course: Focus on a single (1-D) independent variable
which we call “time”.
Continuous-Time (CT) signals: x(t), t — continuous values
Discrete-Time (DT) signals: x[n], n — integer values only

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CT Signals
• Most of the signals in the physical world are CT
signals—E.g. voltage & current, pressure,
temperature, velocity, etc.

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DT Signals
• Examples of DT signals in nature:
— DNA base sequence
— Population of the nth generation of certain
species
• x[n], n — integer, time varies discretely

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ECG Signals
I -D Signals

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Many human-made DT Signals
Ex.#1 Weekly Dow-Jones
industrial average
Why DT? — Can be processed by modern digital computers
and digital signal processors (DSPs).
Ex.#2 digital image

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SYSTEMS
For the most part, our view of systems will be from an
input-output perspective:
A system responds to applied input signals, and its response
is described in terms of one or more output signals

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• An RLC circuit
• Dynamics of an aircraft or space vehicle
• An algorithm for analyzing financial and economic
factors to predict bond prices
• An algorithm for post-flight analysis of a space launch
• An edge detection algorithm for medical images
EXAMPLES OF SYSTEMS

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SYSTEM INTERCONNECTIONS
• An important concept is that of interconnecting systems
— To build more complex systems by interconnecting
simpler subsystems
— To modify response of a system
• Signal flow (Block) diagram
Cascade
Feedback
Parallel +
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