signal & system unit-1
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Signal & System
Signal & system
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2Signal & system
Unit-1Signals
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What is a Signal?
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Signal & system
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What is a Signal?Anything which carries information is a signal.
human voice,
chirping of birds,
smoke signals,
gestures (sign language)fragrances of the Àowers
Signals: The Mathematical Way
A signal is a real (or complex) valued function of one or more real variable(s).
one-dimensional signal :- when the function depend on one variable.
Multi ±dimensional signal :- when the function depend on more than one variable.
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Signal & system
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What is a System?
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Signal & system
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What is a system?
Examples of systems include :
1. An oscilloscope: takes a voltage signal as i/p , produce a 2-dimensional image of the voltage signal.
2. A computer monitor: takes voltage pulses from the CPU as inputs and outputs a time varying display.
1.1. Systems are physical models which process the information signalSystems are physical models which process the information signal
2.2. System gives out an output signal in response to an input signalsSystem gives out an output signal in response to an input signals
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Signal & system
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What is a Signal processing ?
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Signal & system
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What is Signal processing?
Processing means operating in some fashion on a signal to extract some useful
informatione.g. we use our ears as input device and then auditory pathways in the brain to extract the
inf ormation. The signal is pr ocessed by a system
The signal processor may be an:-
electronic system, a mechanical system or even it might be a computer program
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Signal & system
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Difference between
Analog Signal processing & Digital Signal processing ?
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Signal & system
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Analog signal processingo analog signal pr ocessing uses elements such as resistors, capacitors, transistors,
diodes etc
o Based on natural ability of the analog system to solve differential equations that
describe a physical system
o The solutions are obtained in real time...
Digital signal processing
Digital signal pr ocessing means that the pr ocessing is done either by a digital hardware or
by a digital computer .
o Relies
on numerical calculati
ons
o The method may or may not give results in real time..
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Signal & system
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Why we use Digital Signal processing ?
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Signal & system
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The advantages of digital approach over
analog approach
o Flexibility: Same hardware can be used to do various kind of signal
processing operation,
o Repeatability: The same signal processing operation can be
repeated again and again giving same results
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Signal & system
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Classification of signals:-
Signal
Continuoustime signal
Discretetime signal
Defined only at discrete times and the independent
variable takes on only a discrete set of values
Defined for a continuum of values
of the independent variable, t.
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Signal & system
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Elementary Signals
There are ten elementary signals that occur
prominently in the study of :-
Digital signals and
Digital signal processing
1. Unit Step signal
2. Unit Impulse signal or Dirac Delta signal
3. Unit Ramp signal
4. Exponential signal
5. Sine signal
Elementary Signals
There are ten elementary signals that occur
prominently in the study of :-
Digital signals and
Digital signal processing
1. Unit Step signal
2. Unit Impulse signal or Dirac Delta signal
3. Unit Ramp signal
4. Exponential signal
5. Sine signal
6. Cosine signal
7. DC signal
8. Sinc signal
9. Rectangular signal
10. Signum signal
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Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
1. Unit Step Signal
°¯®
u!
0for 0
0for 1
n
nnu
°¯®
u!
0for 0
0for 1
t
t t u
Graphically it as shown below Graphically it as shown below
The unit step function is discontinuous at the origin
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Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
Graphically it as shown below
2. Unit Impulse Signal or Dirac Delta Signal
°¯®
{
!!(
0for 0
0for 1
n
nn
´
g
g
!1dt t H
? A 0!t H 0{t
Note:-
The Impulse function is not an ordinary function
Ordinary function defined for all values of t.
The impulse function is 0 everywhere except at t = 0
where it is undefined
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Signal & system
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Relationship Between D.T. unit impulse & D.T. unit step signals
)1()()( ! nununH
)()(0
k nnu ! §
g
H
We can obtain a D.T. unit step signals u(n) by taking the sum of unit samples
We can obtain a D.T. unit impulse signals from a D.T. unit step signal .
Signal & system
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Important properties of unit impulse signal
P1). Sampling (or shifting) property:- Area under the pr oduct of a function x(t) with deltafunction is equal to the value of that function at that instant where the unit impulse is located
´g
g
! )()()(00t xdt t t t x H
P2). Replication property:- Convolution of any function with delta function yields the same function
0),(1
)( {! EHE
EH t t
P3). Scaling property:-
)()()( t xdt t t x !H
Signal & system
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Example :
1
Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
3. Unit Ramp Signal
°¯®
u!
0for 0
0for
n
nnnr
°¯®
u!
0for 0
0for
t
t t t r
Graphically it as shown belowGraphically it as shown below
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Signal & system
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4.Exponential Signal
at Cet x !
Defined by:-
Here
The constants C and a are real constants
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Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
5. Sine Signal
)sin(wt At x ! )sin(wn An x !
Here ,
A = Amplitude
W= Angular frequency
Graphically it as shown below
Here ,
A = AmplitudeW= Angular frequency
Graphically it as shown below
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Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
6. Cosine Signal
)cos(wt At x ! )cos(wn An x !
Here ,
A = Amplitude
W= Angular frequency
Graphically it as shown below
Here ,
A = Amplitude
W= Angular frequency
Graphically it as shown below
Signal & system
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Continuous time Discrete time
Defined by:- Defined by:
7. DC Signal
At x ! At x !
Here ,
A = Amplitude
Graphically it as shown below
Here ,
A = Amplitude
Graphically it as shown below
Signal & system
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Defined by:-
8. Sinc Signal
t
t At c
T
T )sin(sin !
Sinc (t) =1 at t=0
Sinc (t) =0 at t=±1 , ±2, ±3 ««.
Note:- Sinc signal has the shape of sine wave .
amplitude (A) decrease as the value of t increase.
0sin pt c gpt When
Signal & system
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9) C.T.Rectangular Signal
±°
±¯® ee!¹¹
º
¸©©ª
¨¼½
»¬-
«
otherwise 022
Tfor
T t A
T
t r ect A
Defined by:-
Here ,
A=Amplitude
2w= width/duration of the pulse
f= variable
°̄
® ee
!¹¹ º
¸
©©ª
¨
¼½
»
¬-
«otherwise 0
w-for
2
wt A
W
f
r ect A
Time Domain
Frequency Domain
Here ,
A=AmplitudeT= width/duration of the pulse
t= variable
Signal & system
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9) D.T. Rectangular Signal
±°
±¯® ee!¹¹
º
¸©©ª
¨¼½
»¬-
«
otherwise 022
N-for
N t A
N
nr ect A
Defined by:-
Time Domain
Here ,
A=AmplitudeN= width/duration of the pulse
n= variable
Signal & system
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10. Signum Signal
Defined by
:-
°¯®
"!
0for 1
0for 1sgn
t
t t
Graphically it as shown below
Signum signal is an
Odd
Anti-symmetric function
Signal & system
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Relationship Between Step , Ramp , & Delta signals
)()()(
)()()( intint
t t ut r
t r t ut
atediffer entiatediffer enti
eg r ateeg r ate
H
H
p p
p p
Signal & system
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1. Deterministic and non-deterministic signals
2. Periodic and non-periodic signals
3. Even and odd signals
4. Energy and power signals
Classification of C.T. & D.T. signalsClassification of C.T. & D.T. signals
Signal & system
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31Signal & system
Deterministic
Deterministicandand
Non Non--DeterministicDeterministicSignalsSignals
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32Signal & system
Deterministic signals Non-Deterministic signals
Described by mathematical
Expression , l
ookup table ,
or some well defined Rule
Can¶t be Described by
mathematical Expressio
n , look
up table , or some well defined
Rule
Can be periodic & Non-periodic Non-Periodic
It¶s possible to determine Amplitude of such signals at a
given instant of Time.
It¶s not possible to determine Amplitude of such signals at a
given instant of Time
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Periodic and NonPeriodic and Non--periodic Signals periodic Signals
Signal & system
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CT signal is said to be periodic if it repeat itself after a fixed time period T0.
0T t xt x !
Periodic signalPeriodic signal
T0 = fundamental period
? A ? A0
N n xn x !
DT signal is said to be periodic if it repeat itself after a fixed time period N0
N0 = fundamental period
Signal & system
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Periodic Condition for C.T. & D.T.
)().1 1 t xt x !
)()().3 21 t xt xt x ! )()().4 21 n xn xn x !
)().2 1 n xn x !
wT
T2!
11
2
wT
T
!
2
1
N
N N !
w N
T2!
2
2
2
w
T T
!1
1
2
w
N T
!2
2
2
w
N T
!
2
1
T
T T !
Signal & system
pnI ntegerso f Ratio
pnI ntegerso f Ratio
Time period=LCM (T1,T2 ) or (N1,N2 )
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Problem based on periodicity
)500cos(25 t t t x T!
)50sin(5)100cos(2 nnn x ! T
t t t x 3sin3)3sin(4 !
)2cos(6)sin( nnt x T!
)4sin(3 t t x !
Signal & system
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Problem based on periodicity
)18sin(412sin10 t t t x TT !
n j
en x¼½»
¬-«
! 4T
)sin(481nn x !
)4cos(6)3sin( nnn x T!
)7cos(45sin t t t x !
Signal & system
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Energy and Power SignalsEnergy and Power Signals
Signal & system
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Energy signalEnergy signal
The total Energy of a Continuous time signal x(t) over an interval is defined as:-
´!2
1
2t
t
dt t x E
21 t t t ee
21 t t t ee
For discrete-time sequence x[n]? A§!
2
1
2
n
n
n x E
A signal is called ³energy signal´ if
? A§´
g!
g!
g
g
g!
g!n
n
n x E
dt t x E
2
2
f or C.T.
f or D.T.
g E 0
Signal & system
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Power signalPower signal
g
!́
gp
N
N
N
n x N
P 2
121lim
g P 0
The total power of a Continuous time signal x(t) is defined as:-
For discrete-time sequence x[n]
g!́
gp
T
T
T
t xT
P 2
2
1lim g! ´
gp
2/
2/
21lim
T
T
T
t xT
P
g! ´
gp
2/
2/
21lim
N
N N
n x N
P
Signal & system
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Energy signals Power signals
0<E< 0<P<
Non-periodic Periodic
Time limited Exist over an infinite time
P=0 E=
Difference b/w Energy signal & power signal
gpp t a s A 0 gp{ t a s A 0
Signal & system
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Problem based on Energy & Power
gg! t f or t t x sin10
Identify wheat her it is an E nergy signal or Pow er S ignal
0"!
a f or et xt a
)(2 t uet x t !
Signal & system
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Even and Odd SignalsEven and Odd Signals
Signal & system
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t xt x !
Even Signal or Symmetrical signal
C.T. Even signal
D. T. Even signal
? A ? An xn x !
Where,
X(t)=value of the signal for positive ³ t ´.
X(-t)=value of the signal for negative ³ t ´.
Where,
X(n)=value of the signal for positive ³ n ´.
X(-n)=value of the signal for negative ³ n´.
Signal & system
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Odd Signal or Antisymmetricalsignal
Odd Signal or Antisymmetricalsignal
C.T. Odd signal
C.T. Odd signal
D. T. Odd signalD. T.
Odd signal
)()( n xn x !
Where,
X(t)=value of the signal for positive ³ t ´.
X(-t)=value of the signal for negative ³ t ´.
Where,
X(n)=value of the signal for positive ³ n ´.
X(-n)=value of the signal for negative ³ n´.
t xt x !
Signal & system
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? At xt xt xo !2
1
Decomposing a C.T. signal intoDecomposing a C.T. signal into Even and Odd PartEven and Odd Part
? At xt xt xe !2
1Even part is given by
:-
Odd part is given by:-
? At xt xt x oe ! A given signal can be
expressed as the
sum of Odd part & Even part
Signal & system
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? An xn xn xo!
2
1
? An xn xn xe !2
1
Even part is given by:-
Odd part is given by:-
? An xn xn x oe ! A given signal can be
expressed as the
sum of Odd part & Even part
Decomposing a D.T. signal intoDecomposing a D.T. signal into Even and Odd PartEven and Odd Part
Signal & system
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1.) Identify Even & Odd Signals:-
Problem based on Even & odd
Signal & system
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2. Function x(t) is shown draw Even & Odd part.
Problem based on Even & odd
Signal & system
X(t)
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Solution :-
Even Part
Signal & system
X(t)
X(-t)
X(t) + X(-t)
1 /2 [X(t) + X(-t)]
X(t)
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Odd Part
Solution :-
Signal & system
X(t) - X(-t)
X(-t)
X(t)
1 /2 [X(t) + X(-t)]
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3. Even & odd Part of a signal are shown in fig draw the signal X(t)
Signal & system
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Solution:-
Signal & system
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4. Find Even & Odd parts of signal
Signal & system
X(t)
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Solution:-
Even part
Signal & system
X(t)
X(- t)
X(t) + X(-t )
1 /2 [X(t) + X(-t)]
X(t)
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Solution:-
Odd part
Signal & system
( )
X(- t)
X(t) + X(-t )
1 /2 [X(t) + X(-t)]