Giáo trình Electronic circuits 1
Contents
1 Introduction
4
4
4
7
9
1.1 Examples of Electronic Communications Applications . . . . . . . . . . . .
1.1.1 Cellular Radio Systems . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.2 Television . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.3 Cable TV System . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Course Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.1 Course Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.2 Course Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2 Diode-circuit Analysis
12
2.1 The Ideal Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Analysis of Simple Diode Circuits- The DC Load Line . . . . . . . . . . . . 18
2.3 Small-. . . . . . 21
2.4 Small-signal Analysis - The AC Load Line . . . . . . . . . . . . . . . . . . 26
2.5 Zener Diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Introduction to Transistor Circuits
30
3.1 Current-flow Mechanism in the Junction Transistor . . . . . . . . . . . . . 30
3.1.1 The Emitter-Base Junction . . . . . . . . . . . . . . . . . . . . . . 32
3.1.2 The Collector-Base Junction . . . . . . . . . . . . . . . . . . . . . . 34
3.2 Current Amplification in the Transistor . . . . . . . . . . . . . . . . . . . . 36
3.3 Graphical Analysis of Transistor Circuits . . . . . . . . . . . . . . . . . . . 42
3.4 Power Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.5 The Infinite Bypass Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.6 The Infinite Coupling Capacitor . . . . . . . . . . . . . . . . . . . . . . . . 54
4 Bias Stab
56
4.1 Quiescent-point Variations Due to Uncertainties in β . . . . . . . . . . . . 56
4.2 The Effect of Temperature on the Quiescent-point . . . . . . . . . . . . . . 57
4.3 Stability-factor Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5 Small-signal Low-frequency Analysis and Design
58
5.1 The Hybrid Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.2 The Common-emitter Configuration . . . . . . . . . . . . . . . . . . . . . . 60
5.3 The Common-base Configuration . . . . . . . . . . . . . . . . . . . . . . . 63
5.4 The Common-collector (Emitter-follower) Configuration . . . . . . . . . . . 65
5.5 Impedance Reflection in Transistor . . . . . . . . . . . . . . . . . . . . . . 67
2
CONTENTS
3
6 Multiple-transistor Circuits
70
6.1 Cascading of Amplifier Stages . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.2 The Difference Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.2.1 Common-mode Rejection Ratio . . . . . . . . . . . . . . . . . . . . 76
6.2.2 A Constant-emitter Current Source . . . . . . . . . . . . . . . . . . 77
6.3 The Darlington Configuration (Compound Amplifier) . . . . . . . . . . . . 80
7 Feedback-amplifier Fundamentals
83
7.1 Basis Concepts of Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.2 The Gains and Impedances of a Voltage Feedback Amplifier . . . . . . . . 89
7.2.1 Voltage Feedback-Current Error . . . . . . . . . . . . . . . . . . . . 89
7.2.2 Voltage Feedback-Voltage Error . . . . . . . . . . . . . . . . . . . . 94
7.3 Feedback Amplifier and the Sensitivity Function . . . . . . . . . . . . . . . 99
7.4 Examples of Basic Feedback-amplifier Analysis . . . . . . . . . . . . . . . . 99
8 The Field-effect Transistor
100
8.1 Introduction to the Theory of Operation of the JFET . . . . . . . . . . . . 100
8.2 Introduction to the Theory of Operation of the MOSFET . . . . . . . . . . 104
8.3 Graphical Analysis and Bias . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.3.1 Biasing the JFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.3.2 Biasing the Enhancement MOSFET . . . . . . . . . . . . . . . . . . 108
8.4 Small-signal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8.4.1 . . . . . . 111
8.4.2 . . . . . . 111
Chapter 1
Introduction
1.1 Examples of Electronic Communications Appli-
cations
1.1.1 Cellular Radio Systems
Antenna
Transmitter
Frequency
Synthesizer
Receiver
Logic Unit
Control Unit
Figure 1.1: General block diagram of a cellular
mobile radio unit.
4
1.1. EXAMPLES OF ELECTRONIC COMMUNICATIONS APPLICATIONS
5
Antenna
Frequency
Converter
(Mixer)
Power
Amplifier
Carrier
(from Frequency
Synthesizer)
Phase
Modulator
Directional
Coupler
Duplexer
(Isolator)
from
Frequency
Synthesizer
to Receiver
Microphone
Automatic
Power
Control
Power
Output
Detector
Audio
Amplifier
DC Amplifier
Figure 1.2: Cellular transmitter.
6
CHAPTER 1. INTRODUCTION
Antenna
RF
Second Frequency
Converter
First Frequency
Converter
Amplifier
Duplexer
(Isolator)
FM
Demodulator
Second IF
Amplifier
First IF
Amplifier
from
Frequency
Synthesizer
from
Frequency
Synthesizer
from Transmitter
DC Amplifier
For Power
Control
Audio
Amplifier
Speaker
Audio
Filter
Band
Pass
Filter
RF: Radio Frequency
IF: Intermediate Frequency
FM: Frequency Modulation
Digital Data
to logic unit
1.1. EXAMPLES OF ELECTRONIC COMMUNICATIONS APPLICATIONS
7
1.1.2 Television
Synchroni-
zation
High-Power
Linear Amplifier
R
Lens
G
B
TV
Camera
Color
Processor
Amplitude
Modulator
Image
Antenna
Oscillator
Duplexer
High-Power
Class C Amplifier
Audio
Amplifier
Microphone
FM
Modulator
Oscillator
Figure 1.4: TV transmitter.
8
CHAPTER 1. INTRODUCTION
Antenna or
Cable Input
to Audio
Detector
Frequency
Converter
Video
RF Amplifier
IF Amplifier
Amplifier
to Picture
Tube
IF Filter
(SAW Filter)
Video
Demodulator
Automatic
Gain Control
from
to Picture
Tube
Color
Processor
Audio
Amplifier
RF Amplifier
from IF
Amplifier
Audio
Detector
FM
Demodulator
Speaker
Figure 1.5: TV receiver.
1.1. EXAMPLES OF ELECTRONIC COMMUNICATIONS APPLICATIONS
9
1.1.3 Cable TV System
Distribution
TV signals
Amplifiers
(from TV
Station or
Satellite)
Feeder Cable
Trunk Cable
Feeder Cable
Frequency
Converter
Amplifier
Amplifier
Headend
Cable
Station
Amplifiers
from
Frequency
Synthesizer
Amplifier
Amplifier
Coaxial Cable
(Drop)
Figure 1.6: The cable TV system.
10
CHAPTER 1. INTRODUCTION
1.2 Course Outline
1.2.1 Course Overview
Number of Credits: 3
Course Objective
To provide insight into the analysis and design of electronic circuits, both discrete and
integrated. This course covers the analysis and design of diode and transistor circuits at
low frequencies. Gain, sensitivity, and impedances are studied in detail from both analysis
and design points of view.
Prerequisite
Circuit Theory, Electronic and semiconductor devices.
Assessment
• Mid-term exam: 20%
• Final-exam: 80%
Documents
• Required textbook: D. L. Schilling, and Charles Belove, Electronic Circuits: Discrete
and Integrated, McGraw-Hill Book Company, 1968, 1990.
• References:
1. Adel S. Sedra, Kenneth Carless Smith, Microelectronic Circuits, Oxford Uni-
versity Press, 4th Edition, 1997.
2. C. Savant, M.S. Roden, G.L. Carpenter, Electronic design - Circuits and Sys-
tems, Benjamin/Cummings Publishing Company, 1991.
3. T.F. Bogart, Electronic devices and circuits, Macmillan Publishing Company,
1991.
4. Sergio Franco, Design with Operational Amplifier and Analog Integrated Cir-
cuits, McGraw-Hill, 1998.
1.2.2 Course Descriptions
1. Diode circuit analysis
• Nonlinear properties. The ideal diode.
• Semiconductor diode theory.
• Analysis of simple diode circuits. The DC load line.
• Zener diodes.
2. Introduction to transistor circuits
1.2. COURSE OUTLINE
11
• Current flow mechanism in the junction transistor.
• Current amplification in the transistor.
• Graphical analysis of transistor circuits.
• Power calculations.
3. Bias stability
• Quiescent-point variations due to uncertainties.
• The effect of temperature on the quiescent-point.
• Stability factor analysis.
4. Small-signal low frequency analysis and design
• The hybrid parameters.
• The common-emitter configuration.
• The common-base configuration.
• The common-collector configuration.
5. The field-effect transistor
• Introduction to the theory of operation of the JFET and MOSFET.
• Gra
• Large signal analysis. Distortion.
• Small-signal analysis.
6. Multiple transistor circuits
• Cascading of amplifier stages.
• The difference amplifier.
• The Darlington configuration.
• The Cascode amplifier.
7. Feedback amplifier fundamentals
• Basic concepts of feedback.
• The
• Feedback amplifiers and the sensitivity function.
• Input and output impedances.
• Introduction to the design of feedback amplifiers.
Chapter 2
Diode-circuit Analysis
• Developing circuit theory for the semiconductor junction diode.
• Graphical techniques including a treatment of DC and AC load lines
are applied to both small and large signals.
2.1 The Ideal Diode
The volt-ampere (vi) characteristic of the ideal diode in Figure 2.1 shows the
nonlinear character of the diode (comparing with the linear vi characteristic
of the ideal resistor). The diode can be thought of as a switch controlled
by the polarity of the source voltage.
iD
iD
ri
+
p terminal
n terminal
vD
vi
vD
0
-
Figure 2.1: The ideal diode and its vi characteristic.
Example 1: Half-wave rectifier (Clipping circuit)
Rectification: Producing a DC voltage from an AC supply. A typical half-
wave rectifier circuit is shown in Figure 2.2.
12
2.1. THE IDEAL DIODE
13
vD
ri
iD
-
+
+
1
RL
9
vL
vi
-
Figure 2.2:
Half-wave rectifier circuit,
ri = 1Ω, RL = 9Ω.
Case (a): Source voltage is sinusoidal, vi = Vim cos ω0t, where Vim =
10V
Kirchhoff’s voltage law:
vi = iDri + vD + iDRL
or
vi − vD
When the ideal diode conducting, vD = 0, so that current iD flows in the
ri
ri
Diode
Diode
iD
iD
+
vL
+
vL
vi
vi
RL
RL
-
-
(a)
(b)
Figure 2.3: Conducting and nonconducting states of the diode rectifier.
positive direction only when vi > 0. When vi < 0, the diode does not
conduct, so iD = 0. Figure 2.3 summarizes conducting and nonconducting
states of the diode rectifier. Based on this figure, the diode current iD is
ꢁ
ꢂ
ꢀ
Vim
ri+RL
cos ω0t when vi > 0,
when vi < 0.
iD =
0
and the load voltage vL is
vL = iDRL
14
CHAPTER 2. DIODE-CIRCUIT ANALYSIS
Figure 2.4: Waveforms in the rectifier circuit of Example 1.
The load voltage vL and the signal voltage vi are sketched in Figure 2.4.
This is a half-wave-rectified sine wave. Its average value is obtained by
ꢃ ꢄ
ꢅ
π
VL,dc
=
(VLm cos ω0t)d(ω0t) =
=
= 2.86V
(2.1)
π
2
2π
π
−
The Fourier series expansion for vL(t) is
ꢃ
ꢄ
1
1
2
2
vL(t) = VLm
+ cos ω0t +
cos 2ω0t −
cos 4ω0t + . . .
(2.2)
π
2
3π
15π
This shows that the effect of the diode generated not only the DC term, the
one at the same frequency as the source, but also the terms at harmonic
frequencies not present in the source.
If the purpose of the circuit is to produce the DC voltage, then the DC
component g vL(t). It is
done by passive filters as in Figure 2.5.
The circuit of Figure 2.5(a) presents a simple RC low-pass filter. For
example, if R and C are adjusted so that RC = 100/ω0 and R ꢀ RL, then
the amplitude of the output voltage Von at the frequency nω0 is
VLn
1 + (nω0RC)2
VLn
ꢆ
Von =
≈
when n ≥ 1
100n
where VLn is the amplitude of the load voltage at the frequency nω0.
2.1. THE IDEAL DIODE
15
L
L
R
R
R
+
+
+
vo
-
+
+
+
C
vo
C
vL
vo
vL
C
vL
C
-
-
-
-
-
(a)
(b)
Figure 2.5: Passive power-supply filters.
Using superposition, the output voltage is
ꢃ
ꢄ
1
1
1
1
vo(t) ≈ VLm
+
sin ω0t +
sin 2ω0t −
sin 4ω0t + . . .
π
200
300π
3000π
Thus, the output voltage consists of a DC voltage VLm/π and a small
ripple voltage vr, where
ꢃ
ꢄ
1
1
vr = VLm
sin ω0t +
sin 2ω0t − . . .
200
300π
The ratio of the rms value of the ripple voltage to the DC voltage is a
measure of the effectiveness of the filter in separating the DC voltage from
the harmonics. For the RC filter above, it follows
1
2
ꢊ
ꢇ ꢈ ꢉ
VLm
280
vr,rms
=
2π[vr(ω0t)]2d(ω0t)
1
2π
VLm
0
ꢁ
ꢂ
ꢋ
1
1
√
=
+
+ . . .
(200)2
(300π)2
2
≈
and
vr,rms
π
≈
≈ 0.011
V
280
Case (b): Repeat case (a), if vi = −5 + 10 cos ω0t
In this case a negative bias is added to the signal. The waveforms of vi and
vL are shown in Figure 2.6. The diode conducts when
π
π
2πn − ≤ ω0t ≤ 2πn +
3
3
16
CHAPTER 2. DIODE-CIRCUIT ANALYSIS
Figure 2.6: Rectifier-circuit waveforms with negative bias.
Thus the load voltage is
ꢀ
π
π
4.5 + 9 cos ωt when 2πn ωt 2πn +
3
vL =
5π
0
when 2πn + ≤ ω0t ≤ 2πn + .
3
3
The average value of vL is
ꢃ ꢄ
ꢅ
π
3
1
VL,dc
=
(−4.5 + 9 cos ω0t)d(ω0t) ≈ 0.98V.
π
3
2π
−
Example 2: Full-wave rectifier
One form of full-wave rectifier is shown in Figure 2.7, it is more efficient to
product a DC voltage with low ripple, found in most DC power supplies.
When vi > 0, D1 is a short circuit, D2 is an open circuit. When vi < 0,
D1 is an opeload current
iL is the same positive direction as in Figure 2.8. The load voltage can be
written as vL = |vi|.
The Fourier series for vL is
ꢃ
ꢄ
2
4
4
vL(t) = VLm
+
cos 2ω0t −
cos 4ω0t + . . .
(2.3)
π
3π
15π
The DC term is 2VLm/π which is twice the DC value of the half-wave
rectifier. If vL is passed through the RC filter as in Figure 2.5(a) with
2.1. THE IDEAL DIODE
17
Secondary
winding
Primary
winding
D1
+
1:1
iL
vL
RL
vi
-
D2
1:1
Ideal
transformer
Figure 2.7: Full-wave rectifier.
Figure 2.8: Full-wave rectifier equivalent circuit and waveforms.
18
CHAPTER 2. DIODE-CIRCUIT ANALYSIS
RC = 100/ω0, then the output ripple voltage is
ꢃ
ꢄ ꢃ
ꢄ
4VLm
3π
1
1
vr =
sin 2ω0t −
sin 4ω0t + . . .
200
2000
and the rms ripple becomes
VLm
vr,rms
≈
210π
The ratio of ripple voltage to DC voltage is
vr,rms
1
≈
≈ 0.0024
VL,dc
420
which is less than that obtained from half-wave rectifier.
2.2 Analysis of Simple Diode Circuits- The DC Load
Line
This section considers simple circuits consisting of independent sources,
diodes and rFigure 2.9 is
analyzed with the actual diode characteristics (not ideal) assumed.
vD
ri
iD
-
+
+
1
RL
9
vL
vi
-
Figure 2.9: Half-wave rectifier circuit.
For the actual diode (neglecting the Zener region), the current and volt-
age are relat
ꢁ
ꢂ
qv
D
mkT
iD = Io exp
−1
(2.4)
where iD: current through diode, A; vD: voltage across diode, V; Io: reverse
saturation current, A; q = 1.6×10−19, C, is electron charge; k = 1.38×10−23
,
J/◦K, is Boltzman’s constant; T: absolute temperature, K; m is empirical
◦
constant between 1 and 2. At room temperature (300◦K),
kT
≈ 25mV
(2.5)
q
2.2. ANALYSIS OF SIMPLE DIODE CIRCUITS- THE DC LOAD LINE
19
From equation (4.4), if vD is negative with magnitude much greater than
mkT/q, the current iD is the reverse saturation current −Io, which is a
function of material, geometry and temperature. If vD is positive with
magnitude much greater than mkT/q, the forward current is
qv
D
mkT
iD ≈ Io exp
(2.6)
Equation (4.4) is sketched in Figure 2.10 for germanium and silicon. The
diode is ”turn on” at approximately 0.2 V for germanium and 0.7 V for
silicon.
Figure 2.10: Diode characteristic. (a) Actual characteristic, (b) Straight-line (piece-
wise linear) characteristic.
The graphical analysis is based on two facts:
• The behavior of the diode is completely characterized at low frequen-
cies by its vi characteristic (nonlinear), which is usually available
graphicmeasurement.
• Other linear elements of the circuit can be replaced by a Th´evenin
equivalent circuit.
Therefore, the circuit in Figure 2.9 can be considered in two parts as
shown in Figure 2.11. The relations for two parts with two unknown vD
and iD can be written
iD = f(vD)
(2.7)
vD = vT − iDRT
(2.8)
20
CHAPTER 2. DIODE-CIRCUIT ANALYSIS
When two parts are connected, these two relations are satisfied simultane-
ously, and the circuit will operate at the point given by the solution of the
equations. The solution can be found analytically if the vi characteristic of
the nonlinear element is known, e. g. the equation (4.4). In Figure 2.11,
the Th´evenin voltage vT = vi and RT = ri + RL.
Thévenin equivalent
of linear portion of circuit
+
iD
RT
vT
Diode or
other nonlinear
element
vD
+
-
-
Figure 2.11: General circuit containing a nonlinear element.
However, if the accuracy required is not great and the behavior of diodes
differs from the theoretical characteristic given by (4.4), then the problem
above can be solved graphically by plotting (2.7) and (2.8) on the same
axes. The intersection of two curves gives the operating point of the circuit
for the particular conditions which determine vD and iD.
An example is shown in Figure 2.12. The straight-line characteristic
of the Th´evenin circuit (usually called the DC load line is drawn for a
DC Th´evenin voltage vT = 1.5 V and Th´evenin resistance RT = 50Ω. The
intersection of DC load line (2.8) and the diode characteristic (2.7) gives the
operating point (often called the quiescent, or Q, point) for these condition.
In Figure 2.e vD ≈ 0.7 V,
iD ≈ 15 mA. If vT changes to 2 V, the DC load line is horizontally shifted
as shown, and the operating point moves to Q2.
As long as RT remains constant, any change in vT corresponds to a
horizontal shift of the load line. Thus, if vT = VTm sin ωt is sinusoidal,
the current waveform iD can be found by choosing several points on the
sine wave and drawing the corresponding load lines to find the resulting
currents. Figure 2.13 shows this technique for VTm = 1.5 V. Note that the
actual diode characteristic causes the distortion in the current waveform
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