Electronics I
EENG 3510
Lecture 2
Shengli Fu
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
1
Ideal transfer characteristic
Figure 1.11 (b) Transfer characteristic of a linear voltage amplifier with voltage gain Av.
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
2
Transfer Characteristic with Saturation
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
3
Nonlinear transfer characteristic and biasing
Figure 1.14 (a) An amplifier transfer characteristic that shows considerable nonlinearity. (b) To obtain linear operation the amplifier is biased as shown,
and the signal amplitude is kept small. Observe that this amplifier is operated from a single power supply, VDD.
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
4
Symbol convention
Total instantaneous
quantities
Lower case symbol +
upper case subscript
iA(t), vC(t)
Direct current
quantities
Upper case symbol +
upper case subscript
IA, VC
Incremental signal
quantities
Lower case symbol +
lower case subscript
ic(t), vc(t)
Sine wave signal
Upper case symbol +
lower case subscript
Ia, Vc
Figure 1.16 Symbol convention employed throughout the book.
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
5
Other Amplifiers Types
Type
Circuit Model
Gain Parameter
Ideal Characteristics
Open-circuit Voltage
Gain
Voltage
Amplifier
Avo= vo / vi (V/V)
Short-circuit Voltage
Gain
Current
Amplifier
Aio= io / ii (A/A)
Short-circuit
Transconductance
Transconductance
Amplifier
Gm= io / vi (A/V)
Transresistance
Amplifier
Open-circuit
Transistance
Rm= vo / ii (V/A)
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Ri = ∞
Ro = 0
Ri = 0
Ro = ∞
Ri = ∞
Ro = ∞
Ri = 0
Ro = 0
Copyright  2004 by Oxford University Press, Inc.
6
Low-pass Filter
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
7
High-pass Filter
Microelectronic Circuits - Fifth Edition
Sedra/Smith
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
Copyright  2004 by Oxford University Press, Inc.
8
Operational Amplifiers
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
9
9
Operational Amplifier
 The name “operational amplifier” originates from the use of
this type of amplifier to perform specific electronic circuit
functions or operations, such as scaling, summation, and
integration.
 Why popular?
• One can do almost anything with op amp
• IC op amp has characteristics that closely approach the
assumed ideal.
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
10
History of Operational Amplifiers
• 1952, K2-W, George A. Philbrick Researches, (Vacuum tubes)
• 1963, µA702, Fairchild, (9 transistor), $300, limited to US military
and Aerospace consumer, first solid state monolithic op amp
• 1965, µA709, Bob Widlar of Fairchild, $70(1965), $2 (1969)
• 1967, LM101, National Semiconductor, increased gain, short-circuit
protection, and simplified frequency compensation
• 1968, µA741, Fairchild, similar performance with LM101, different
frequency compensation
• 1974, RC4558, Raytheon Semiconductor, first multiple op amp
• 1975, CA3130, RCA, first FET op omp
• 1976, TL084, Texas Instruments,
• 2006, µA741CD, Texas Instruments, $0.14
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
11
2.1 The Ideal OP AMP
2.1.1 The Op-Amp Terminals
inverting input terminal
output terminal
noninverting input terminal
Circuit symbol for the op amp
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
12
2.1 The Ideal OP AMP
2.1.1 The Op-Amp Terminals (cont.)
•
•
•
No terminal of the op-amp
package is physically
connected to ground
An op-amp may have
other terminals for specific
purposes: frequency
compensation, offset
nulling, etc.
We will omit power-supply
terminals
Figure 2.2 The op amp shown connected to dc power supplies.
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
13
2.1 The Ideal OP AMP
2.1.1 The Op-Amp Terminals (cont.)
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
14
2.1 The Ideal OP AMP
Application examples
LM386:
http://www.national.com/mpf/LM/LM386.html#Overview
LM4950: http://www.national.com/mpf/LM/LM4950.html#Overview
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
15
2.1 The Ideal OP AMP
2.1.2 Function and Characteristics of the Ideal Op-amp
The op amp is designed to sense the difference between the voltage signals
applied at its two input terminals, multiply this by a number of A, and cause the
resulting voltage A(v2-v1) to appear at output terminal.
• No input current, in
other words, the input
impedance is infinite
• The voltage of output
terminal is always
A(v2-v1), independent
of the output current, in
other words, the output
impedance is zero
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
16
2.1 The Ideal OP AMP
2.1.2 Function and Characteristics of the Ideal Op-amp (cont.)
Characteristics of the Ideal Op-amp
1.
Infinite input impedance
2.
Zero output impedance
3.
Zero common-mode gain or
equivalent, infinite common-mode
rejection
4.
Infinite bandwidth
5.
Infinite open-loop gain A
Figure 2.3 Equivalent circuit of the ideal op amp.
Dr. Shengli Fu
Department of Electrical Engineering
University of North Texas
17