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ELCT 371: Electronics
Pre-Req: CSCE 211, ELCT 222
Dr. Goutam Koley
Room 3A12, 777- 3469, [email protected]
Lecture Hours: Tue & Thurs 12.30 – 1:45 AM
SWGN 2A15
Office Hours: Tue and Thurs 2.30 – 3.30, and by
appointment
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Objective
Objective: To learn the basics of analog circuit design
and analysis
Text book: Electronics, by Allan R. Hambley, 2nd Edition, Prentice
Hall, Upper Saddle River, NJ 07458, 2000
ISBN # 0136919820
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Schedule and Grading
Class: Jan 12 – April 22; 28 lecture days.
Final Exam: Wednesday, April 28, 2010; at 2.00 pm.
Grading:
Homeworks:
Pop Quiz
Midterms:
Final:
Grades (Total 100 points):
A: 90 - 100
B+ : 85 – 90
C: 70 – 74
D+: 65 – 69
(6)
(4)
(2)
(1)
B: 80 – 84
D: 60 – 64
12 %
16 %
32 %
40 %
C+ : 75 - 79
F: <60
All grades will be normalized. The highest overall individual score (out of 100) will
be made 100, and all the others will be multiplied by the ratio before assigning the
final grade. If there are confusions regarding any grading please bring it to my
attention immediately after the grading is done. Otherwise, you may not get benefit
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of any corrections.
Some reminders…




Eating or drinking in class is NOT preferable. However, if
you absolutely have to, you must not disturb others.
Do not enter the class if you are more than 15 minutes
late, without very valid reasons
No retake of exams/tests permitted unless you let me know
prior to the test/exam and have valid reasons
PLEASE ADHERE TO THE UNIVERSITY OF SOUTH
CAROLINA HONOR CODE (No cheating in any form!!!)
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1.4 Basic Amplifier Concepts
An ideal amplifier produces an output signal with a larger amplitude while
maintaining the same waveshape
Microphone Amplifier
1 mV
Loudspeaker
Av=10,000
10 V output
v0 (t )  Avvi (t )(1.2)
vi  input voltage
v0  output voltage
Av  voltage gain
Fig. 1.15
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1.4 Basic Amplifier Concepts
Inverting and Noninverting Amplifiers:
Inverting Amplifier
Noninverting Amplifier
Av 
is a negative number
Av 
is a positive number
v0 (t )  Avvi (t )(1.2)
Fig. 1.16
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1.4 Basic Amplifier Concepts
The Voltage-Amplifier Model
Input impedance Zi for a typical
oscilloscope is a 1 MW resistance in
parallel with 47 pF capacitance
Fig. 1.17
vs is the source voltage
Avo is the open circuit voltage gain
Rs is the source resistance
Ri is the input resistance of the amplifier
RL is the load resistance
Ro is the output resistance of the amplifier
Ri is the equivalent resistance looking into the input terminals of the amplifier and
Ro is the same looking into the output terminals
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1.4 Basic Amplifier Concepts
The Voltage-Amplifier Model
•
•
•
Real amplifiers cannot deliver a fixed voltage to an arbitrary load resistance
Output voltage changes with load resistance - Higher for larger RL and lower
for smaller RL
The amplifier output resistance accounts for the reduction in output voltage
Fig. 1.17
Avo is the open circuit voltage gain of the amplifier, meaning the load is infinite.
Thus there is no drop across the resistances, and v0 = Avovi
• Actual amplifier voltage gain Av=v0/vi is always smaller than Avo
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1.4 Basic Amplifier Concepts
Current Gain
i0
Ai 
ii
i0 v0 / RL
Ri
Ai  
 Av
ii vi / Ri
RL
v0
Av 
vi
is the voltage gain with the load
resistor connected. Note that Av is
smaller than Av0
Fig. 1.17
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1.4 Basic Amplifier Concepts
Power Gain
•
Assuming the input impedance and load impedance are purely resistive, the
average power is the product of the rms current and rms voltage.
Fig. 1.17
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1.4 Basic Amplifier Concepts
Example 1.1: Find voltage gain, current gain, and power gain for the
circuit below
Fig. 1.18
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1.5 Cascaded Amplifiers
Fig. 1.19
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1.5 Cascaded Amplifiers
Example 1.2 Analysis of a Cascaded Amplifier
Fig. 1.20
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1.5 Cascaded Amplifiers
Power gain:
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1.5 Cascaded Amplifiers
Simplified Models for Cascaded Amplifier Stages
Example 1.3 Determining the Overall Model of a Cascaded Amplifier
Fig. 1.20
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1.5 Cascaded Amplifiers
Fig. 1.21 Simplified model for the cascaded amplifiers of Fig. 1.20
Question: Who provides the power to amplify the input signal?
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1.6 Power Supplies and Efficiency


Power supply delivers current from several dc voltages to the amplifier
The total power supplied is the sum of the powers supplied by each voltage
source
Fig. 1.22
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1.6 Power Supplies and Efficiency
Fig. 1.23
Here, Pi = power entering the amplifier from the signal source
Ps = power from the power supply
P0 = output power
Pd = dissipated power
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1.6 Power Supplies and Efficiency
Power Efficiency:
Example 1.4 Determining the Power Efficiency of an Amplifier
Fig. 1.24
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1.6 Power Supplies and Efficiency
Fig. 1.24
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1.7 Decibel Notation

Power gain is often expressed in decibels (dB) as

An attenuator having the output power smaller than the input power, has a
negative decibel gain
The overall gain for cascaded amplifiers is the product of the power gains of
the individual amplifiers

; [expressed in decibels]
Finally,

Power gain can be computed from voltage gain, input resistance and output
resistance as given by equation (1.6)
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1.7 Decibel Notation
[Converted to decibels]
Therefore,
Voltage and Current Gains Expressed in Decibels
[Voltage gain converted to decibels]
[Current gain converted to decibels]
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