ELCT 371: Electronics Pre-Req: CSCE 211, ELCT 222 Dr. Goutam Koley Room 3A12, 777- 3469, [email protected]@engr.sc.edu Lecture Hours: Tue & Thurs.

ELCT 371: ElectronicsPre-Req: CSCE 211, ELCT 222 Dr. Goutam Koley

Room 3A12, 777- 3469, [email protected]

Lecture Hours: Tue & Thurs 12.30 – 1:45 AMSWGN 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, 2000ISBN # 0136919820

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Schedule and Grading

Grading: Homeworks: (6) 12 %Pop Quiz (4) 16 %Midterms: (2) 32 %Final: (1) 40 %

Class: Jan 12 – April 22; 28 lecture days.

Final Exam: Wednesday, April 28, 2010; at 2.00 pm.

Grades (Total 100 points):A: 90 - 100 B+ : 85 – 90 B: 80 – 84 C+ : 75 - 79C: 70 – 74 D+: 65 – 69 D: 60 – 64 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 of any corrections. 3

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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An ideal amplifier produces an output signal with a larger amplitude while

maintaining the same waveshape

1.4 Basic Amplifier Concepts

)2.1()()(0 tvAtv iv

iv input voltage

0v output voltage

vA voltage gain

Microphone

1 mV

Amplifier

Av=10,000

Loudspeaker

10 V output

Fig. 1.15

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Inverting and Noninverting Amplifiers:

1.4 Basic Amplifier Concepts

)2.1()()(0 tvAtv iv

vAInverting Amplifier is a negative number

Noninverting Amplifier vA is a positive number

Fig. 1.16

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The Voltage-Amplifier Model

1.4 Basic Amplifier Concepts

Fig. 1.17

vs is the source voltage

Rs is the source resistance

RL is the load resistance Ro is the output resistance of the amplifier

Ri is the input resistance of the amplifier

Ri is the equivalent resistance looking into the input terminals of the amplifier andRo is the same looking into the output terminals

Input impedance Zi for a typical oscilloscope is a 1 Mresistance in parallel with 47 pF capacitance

Avo is the open circuit voltage gain

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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

1.4 Basic Amplifier Concepts

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

Fig. 1.17

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1.4 Basic Amplifier Concepts

Fig. 1.17

ii i

iA 0

Current Gain

L

iv

ii

L

ii R

RA

Rv

Rv

i

iA

/

/00

iv v

vA 0

is the voltage gain with the loadresistor connected. Note that Av is

smaller than Av0

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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.

1.4 Basic Amplifier Concepts

Fig. 1.17

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Example 1.1: Find voltage gain, current gain, and power gain for the circuit below

1.4 Basic Amplifier Concepts

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Fig. 1.18

1.5 Cascaded Amplifiers

Fig. 1.19

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1.5 Cascaded Amplifiers

Fig. 1.20

Example 1.2 Analysis of a Cascaded Amplifier

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1.5 Cascaded Amplifiers

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Power gain:

Simplified Models for Cascaded Amplifier Stages

Example 1.3 Determining the Overall Model of a Cascaded Amplifier

Fig. 1.20

1.5 Cascaded Amplifiers

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Fig. 1.21 Simplified model for the cascaded amplifiers of Fig. 1.20

1.5 Cascaded Amplifiers

Question: Who provides the power to amplify the input signal?

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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

1.6 Power Supplies and Efficiency

Fig. 1.22

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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

1.6 Power Supplies and Efficiency

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Power Efficiency:

Example 1.4 Determining the Power Efficiency of an Amplifier

Fig. 1.24

1.6 Power Supplies and Efficiency

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Fig. 1.24

1.6 Power Supplies and Efficiency

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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

Power gain can be computed from voltage gain, input resistance and output resistance as given by equation (1.6)

1.7 Decibel Notation

; [expressed in decibels]

Finally,

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[Converted to decibels]

Therefore,

Voltage and Current Gains Expressed in Decibels

[Voltage gain converted to decibels]

[Current gain converted to decibels]

1.7 Decibel Notation

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