1. Leo Lam © 2010-2011 Signals and Systems EE235 Today’s Cultural Education: Liszt: Von der Wiege bis zum Grabe, Symphonic Poem No. 13

2. Leo Lam © 2010-2011 Arthur’s knights Who was the largest knight at King Arthur’s round table? Sir Cumfrence, he got his size from eating too much pie.

3. Leo Lam © 2010-2011 Today’s menu Homework 1 due today! Lab starts tomorrow Dirac Delta Function (cont’) System properties –Linearity –Time invariance –Stability –Invertibility –Causality –Memory

4. Recap: Dirac Delta function δ(t) Leo Lam © 2010-2011 “a spike of signal at time 0” 0 It has height = , width = 0, and area = 1 δ(t) Rules 1.δ(t)=0 for t≠0 2.Area: 3. If x(t) is continuous at t 0, otherwise undefined

5. Scaling the Dirac Delta Proof: Suppose a>0 a<0 Leo Lam © 2010-2011

6. Scaling the Dirac Delta Proof: Generalizing the last result Leo Lam © 2010-2011

7. Multiplication of a function that is continuous at t 0 by δ(t) gives a scaled impulse. Sifting Properties Relation with u(t) Summary: Dirac Delta Function Leo Lam © 2010-2011

8. Evaluate Dirac Delta – Another one Leo Lam © 2010-2011

9. Is this function periodic? If so, what is the period? (Sketch to prove your answer) Slightly harder Leo Lam © 2010-2011 Not periodic – delta function spreads with k 2 for t>0 And x(t) = 0 for t<0

10. Energy and power The energy of a signal Definition: An energy signal is any signal such that: Physically: this signal has finite energy Leo Lam © 2010-2011

11. Power The power of a signal Definition: A power signal is any signal such that: Physically: this signal has finite average power Leo Lam © 2010-2011

12. Signal power and energy What is the energy of u(t) Leo Lam © 2010-2011 Why?

13. Signal power and energy What is the power of u(t) Leo Lam © 2010-2011

14. Summary: Signal energy/power Defined Energy and Power of signals Defined Energy signal/Power signal Leo Lam © 2010-2011

15. System Leo Lam © 2010-2011 delay amplifier integrator sifter x(t)

16. System properties Leo Lam © 2010-2011 Linearity: A System is Linear if it meets the following two criteria: Time-invariance: A System is Time-Invariant if it meets this criterion Ifand Then If Then IfThen “System Response to a linear combination of inputs is the linear combination of the outputs.” “System Response is the same no matter when you run the system.”

17. System properties Leo Lam © 2010-2011 Stability: A System is BIBO Stable if it meets this criterion Invertibility: A System is Invertible if it meets this criterion: “If you know the output signal, then you know exactly what the input signal was.” BIBO = “Bounded input, bounded output” If Then “The system doesn’t blow up if given reasonable inputs.” You can undo the effects of the system. If

18. System properties Leo Lam © 2010-2011 Causality: A System is Causal if it meets this criterion Memory: A System is Memoryless if it meets this criterion “The output depends only on the current value of the input.” “The system does not anticipate the input.” (It does not laugh before it’s tickled!) The output depends only on current or past values of the input. If T{x(t)}=y(t) then y(t+a) depends only on x(t+b) where b<=a If T{x(t)}=y(t) then y(t+a) depends only on x(t+a) (If a system is memoryless, it is also causal.)

19. Summary: System properties Leo Lam © 2010-2011