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Electrical Engineering 348: ELECTRONIC CIRCUITS I

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Electrical Engineering 348: ELECTRONIC CIRCUITS I Dr. John Choma, Jr. Professor of Electrical Engineering University of Southern California Department of Electrical ... – PowerPoint PPT presentation

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Title: Electrical Engineering 348: ELECTRONIC CIRCUITS I


1
Electrical Engineering 348ELECTRONIC
CIRCUITS I
  • Dr. John Choma, Jr.
  • Professor of Electrical Engineering
  • University of Southern California
  • Department of Electrical Engineering
  • Electrophysics
  • University Park Mail Code 0271
  • Los Angeles, California 90089-0271
  • 213-740-4692 Office
  • 626-715-0944 Fax
  • 818-384-1552 Cell
  • johnc_at_almaak.usc.edu
  • Spring Semester 2001

2
EE 348Lecture Supplement Notes SN1
  • Review of Basic Circuit Theory
  • and
  • Introduction To Fundamental
  • Electronic System Concepts
  • 01 January 2001

3
Outline Of Lecture
  • Thévenins Nortons Theorems
  • Basic Electronic System Concepts
  • Steady State Sinusoidal Response
  • Transient Response

4
Thevénins Theorem
  • Concept
  • Two Terminals Of Any Linear Network Can Be
    Replaced By Voltage Source In Series With An
    Impedance
  • Thévenin Voltage Is Open Circuit Voltage At
    Terminals Of Interest
  • Thévenin Impedance Is Output Impedance At
    Terminals Of Interest
  • Linear Load
  • Thévenin Concept Applies To Linear Or Nonlinear
    Load
  • Voltage VL Is Zero If No Independent Sources Are
    Embedded In The Load

5
Thévenin Model Parameters
  • Thévenin Voltage
  • Zero Load Current
  • Voc ? Vth
  • Thévenin Impedance
  • Ohmmeter Calculation
  • Thévenin Voltage Is Set To
  • Zero By Nulling All Independent
  • Sources In Linear Network
  • Superposition

6
Thévenin Example
  • Bipolar Emitter Follower Equivalent Circuit
  • Load Is The Capacitor, Cl
  • Calculate
  • Thévenin Voltage Seen By Load
  • Thévenin Impedance Seen By Load
  • Transfer Function, Vo(s)/Vs(s)
  • 3dB Bandwidth

7
Thévenin Voltage And Impedance
  • Thévenin
  • Voltage Gain
  • Thévenin
  • Impedance

8
Thévenin Output Model
  • Gain
  • Resistance

9
Transfer Function (Gain)
  • Gain At Zero Frequency Is Ath
  • Bandwidth Definition
  • 3dB Bandwidth (Radians/Sec)

10
Frequency and Phase Responses
0.776
45
11
Input Impedance
  • Very Large Zero Frequency Input Impedance
  • Other Characteristics
  • Left Half Plane Pole And Left Half Plane Zero
  • Non-Zero High Frequency Impedance

12
Voltage Delivery To Load
  • Load Voltage
  • If Zl ltlt Zs, Much Of The Source Voltage Is
    Lost In The Source Impedance
  • If Zl Zs, 50 Of The Source Voltage Is
    Lost, Resulting In A factor Of Two Attenuation Or
    6 dB Gain Loss.
  • Many Systems Are Intolerant Of Such A Loss
  • System Problem
  • Voltage Generated By Some Linear Network Is To Be
    Supplied To A Fixed Load Impedance, Zl
  • Because The Source Network Is Linear, Its Output
    Can Be Represented By A Thévenin Circuit (Vs
    Zs)
  • Assume Thévenin Source and Load Impedances are
    Fixed

13
Insertion Of Voltage Buffer
14
Impact Of Voltage Buffer
  • Practical Buffer
  • Zout Very Small
  • Zin Very Large
  • Abuf Near Unity
  • Effect Of Ideal Buffer

15
Nortons Theorem
  • Concept
  • Two Terminals Of Any Linear Network Can Be
    Replaced By A Current Source In Shunt With An
    Impedance
  • Norton Current Is Short Circuit Current At
    Terminals Of Interest
  • Norton Impedance Is Output Impedance At Terminals
    Of Interest And Is Identical To Thévenin Output
    Impedance
  • Linear Load
  • Norton Concept Applies To Linear Or Nonlinear
    Load
  • Voltage VL Is Zero If No Independent Sources Are
    Embedded In The Load

16
Norton Model Parameters
  • Norton Current
  • Zero Load Voltage
  • Isc ? Ino
  • Norton Impedance
  • Ohmmeter Calculation
  • Norton Current Is Set To
  • Zero By Nulling All
  • Independent Sources In
  • Linear Network
  • Superposition

17
ThéveninNorton Relationship
  • From Thévenin Model
  • From Norton Model
  • ThéveninNorton Equivalence

18
Current and Voltage Sources
  • Ideal Voltage
  • Source
  • Ideal Current
  • Source

19
Voltage Amplifier
  • Ideal Properties
  • Infinitely Large Input Impedance, Zin
  • Zero Output Impedance, Zout
  • Sufficiently Large Voltage Gain, Av, Independent
    Of Input Voltage, VI and Output Voltage Vo
  • Circuit Schematic
  • Symbol

20
Transconductor
  • Ideal Properties
  • Infinitely Large Input Impedance, Zin
  • Infinitely Large Output Impedance, Zout
  • Sufficiently Large Transconductance, Gm,
    Independent Of Input Voltage, VI and Output
    Voltage Vo
  • Circuit Schematic
  • Symbol

21
Current Amplifier
  • Ideal Properties
  • Zero Input Impedance, Zin
  • Infinitely Large Output Impedance, Zout
  • Sufficiently Large Current Gain, Ai, Independent
    Of Input Voltage, VI and Output Voltage Vo
  • Circuit Schematic
  • Symbol

22
Transresistance Amplifier
  • Ideal Properties
  • Zero Input Impedance, Zin
  • Zero Output Impedance, Zout
  • Sufficiently Large transresistance, Rm,
    Independent Of Input Voltage, VI and Output
    Voltage Vo
  • Circuit Schematic
  • Symbol

23
Max Voltage Current Transfer
  • Voltage
  • Transfer
  • Current
  • Transfer

? Maximum Voltage Transfer Requires Very Small
Zth
? Maximum Current Transfer Requires Very Large
Zth
24
Power Dissipated In The Load
  • Sinusoidal Steady State
  • Load Power

25
Maximum Power Transfer
  • Condition
  • Max Power

26
Example50 ? Transmission Line
  • Parameters
  • Antenna RMS Voltage Signal Is 10 ?V
  • Transmission Line Coupling To RF Stage Behaves
    Electrically As A 50 Ohm Resistance
  • Power To RF Input Port
  • Maximized When RF Input Impedance Is 50 Ohms
  • dBm Value

27
Second Order Lowpass Filter
  • Lowpass Filter
  • Unity Gain Structure (Gain At Zero Frequency Is
    One)
  • Ideal Transconductors
  • KVL
  • (Solve For Vo/Vs)

28
Filter Transfer Function
  • Generalization
  • Parameters
  • DC Gain H(0) 1
  • Undamped Resonant Frequency ?o
    (gm1gm2/C1C2)1/2
  • Damping Factor ? (gm2C1 / 4gm1C2)1/2

29
Lowpass 2nd Order Function
  • Poles At s p1 s p2
  • Undamped Frequency
  • Damping Factor
  • P1 P2 Real Results In ? gt1 (Overdamping) Or ?
    1 (Critical Damping)
  • P1 P2 Complex Requires P1 P2 Conjugate Pairs,
    Whence ? lt 1 (Underdamping)

30
Lowpass Critical Damping
  • Critical Damping ? ? 1 ? p1 p2
  • Frequency Response
  • Bandwidth Constraint
  • Bandwidth

H(j?) in dB
H(0)
Slope 40 db/dec
-3 dB
?
B
31
Lowpass Overdamping
  • Overdamping ? ? gt 1 ? p1 lt p2
  • Poles Are Real Numbers
  • Dominant Pole System Implies p1 ltlt p2
  • Dominant Pole Bandwidth
  • Transfer Function Approximation
  • Bandwidth Approximation
  • Gain-Bandwidth Product

32
Lowpass Frequency Response
3-dB Down
33
Lowpass Phase Response
34
Lowpass Step Response
  • Input Is Unit Step X(s) 1/s
  • Overdamped (? gt 1)
  • Critical Damping (? 1 ? ?o p1 p2)

35
Real Pole Step Response Plots
95 Line
36
Lowpass Underdamping
  • Overdamping ? ? lt 1 ? p1 p2 ?oe j?
  • Circuit Bandwidth
  • Proportional To ?o
  • Equal To ?o For ? 0.707
  • Frequency Response Peaking
  • H(j?) Not Monotone Decreasing Frequency
    Function If ? lt 0.707
  • Non-Zero Frequency Associated With Maximal
    H(j?)

37
Underdamped Frequency Response
3-dB Line
38
Underdamped Phase Response
39
Delay Response
  • Steady State Sinusoidal Response
  • If Phase Angle Is Linear With Frequency
  • Constant Time Shift, Independent Of Signal
    Frequency
  • No Phase Angle Is Ever Perfectly Linear Over
    Entire Passband
  • Envelope Delay

40
Underdamped Delay Response
41
Underdamped Step Analysis
  • Input Is Unit Step X(s) 1/s
  • Underdamped (? lt 1)
  • Characteristics
  • Damped Oscillations
  • Oscillation For Zero Damping (? 0)
  • Undamped Frequency Is Oscillatory Frequency For
    Zero Damping

42
Underdamped Step Response
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