Signals & Systems
Final Review
Email:penghe@cqu.edu.cn
Tel:+86-23-65111163
Lab of Optoelectronic Measurement and Imaging,
Department of Optoelectronics Engineering, Chongqing University
CHAPTER 1
Signals & Systems
Chapter 1: Signals & Systems
1. Continuous-time and Discrete-time signals
Signals: functions of one or more independent variables
Continuous-time signal: signals are defined for a
continuum of values of the independent variable;
2. Energy & Power
Energy over t1 t t2:
Average power:
♠
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2121)()(2ttttdttxdttp2121)(1)(121212ttttdttxttdttptt
Chapter 1: Signals & Systems
Total Energy:
(when t1→∞, t2→∞)
Average Power:
♠
Finite Energy Signal :
Finite Power Signal :
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( P 0 )
( E )
dttxdttxETTT22)()(limTTTdttxTP2)(21limdttxE2)(TTTdttxTP2)(21lim
Chapter 1: Signals & Systems
3. Examples of Transformations
A. Time Shift
Replace the independent variable t in the signal x(t) by t-t0
t0>0
t0<0
x(t) x(t-t0)
Right Shift
Left Shift
Delayed
Advanced
B. Time Reversal
x(t) x(t)
C. Time Scaling
x(t) x(at)
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Chapter 1: Signals & Systems
Replace t by at+b (a&b are real constants)
x(t)
x(at+b)
|a|>1:
Time Compressed
|a|<1:
Time Stretched
♠
a<0:
Time Reversal
b≠0:
Time Shift (b>0, left shift; b<0, right shift)
(b>0, advanced; b<0, delayed)
First Shift
Then Scaling
Finally Reversal
Example 1.1~1.3(Illustration)
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Chapter 1: Signals & Systems
4 Periodic Signals:
There is a positive value of T which :
x(t)=x(t+T) , for all t x(t) is periodic with period T .
The smallest T Fundamental Period T0
x1(t) = Acos(3t)+ Bsin(2t)
♠
It is the sum of two periodic signals with T1= 2/ 3, T2=
.
x1(t) is periodic. T0 The smallest multiples of T1 and
T2 in common, T0 = 2.
x2(t) = Acos(t)+ Bsin(2t)
It is the sum of two periodic signals with T1= 2, T2= .
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x2(t) is aperiodic.
Chapter 1: Signals & Systems
Inversely
proportional
Frequency(Hz)
Euler’s Relation:
♠
and