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Chapter 2
Basic Concepts of Electronics
I
-
+
-
+
Electron
-
(a)
+
(b)
Figure 2.1 Electric current within a conductor. (a) Random movement of electrons
generates no current. (b) A net flow of electrons generated by an external force.
l
I
Vb
E
Va
Figure 2.2 A model of a straight wire of length l and cross-sectional area A. A potential
difference of Vb – Va is maintained across the conductor, setting up an electric field E. This
electric field produces a current that is proportional to the potential difference.
First digit (A)
Multiplier (C)
Second digit (B)
Tolerance (D)
Figure 2.3 The colored bands that are found on a resistor can be used to determine its
resistance. The first and second bands of the resistor give the first two digits of the
resistance, and the third band is the multiplier which represents the power of ten of the
resistance value. The final band indicates what tolerance value (in %) the resistor possesses.
The resistance value written in equation form is AB10C  D%.
Color
Number
Black
0
Brown
1
Red
2
Orange
3
Yellow
4
Green
5
Blue
6
Violet
7
Gray
8
White
9
Gold
–1
5%
Silver
–2
10%
Colorless
Tolerance (%)
20%
Table 2.1 The color code for resistors. Each color can indicate a first or second digit, a
multiplier, or, in a few cases, a tolerance value.
R
I
+
V
R1
R2
+ 10 W -
+ 20 W -
V1
V2
-
I
(a)
VS = 30 V
(b)
Figure 2.4 (a) The voltage drop created by an element has the polarity of + to – in
the direction of current flow. (b) Kirchhoff’s voltage law.
I1
I2
6A
3A
I3
(a)
II==?9 A
(b)
Figure 2.5 (a) Kirchhoff’s current law states that the sum of the currents entering a
node is 0. (b) Two currents entering and one “negative entering”, or leaving.
a
4W
b
e
10 V
+
+
6W
14 V
-
2W
I1
d
c
I3
f
I2
Figure 2.6 Kirchhoff’s current law example.
A
+
30 V
-
+ 20 W -
C
+ 20 W -
V
+
20 W
-
B
+
-
20 V
Figure 2.7 Example of nodal analysis.
1 mV
Rs
100 kW
Electrocardiogram
Vo
1 MW
Ri
Figure 2.8 The 1 mV signal from the electrocardiogram is attenuated by the
resistive divider formed by the 100 kW skin resistance and the 1 MW input
resistance of the oscilloscope.
vi
Slider
vo
Figure 2.9 A potentiometer is a three-terminal resistor with an adjustable sliding
contact shown by the arrow. The input signal vi is attenuated by the potentiometer
to yield an adjustable smaller voltage vo.
Galvanometer
Galvanometer
Rp
(a)
Rs
(b)
Figure 2.10 (a) When a shunt resistor, Rp, is placed in parallel with a galvanometer,
the device can be used as an ammeter. (b) When a resistor, Rs, is connected in series
with the galvanometer, it can be used as a voltmeter.
I1
I2
+
R1
-
R1
b
a
R3
Rx
Figure 2.11 A circuit diagram for a Wheatstone bridge. The circuit is often used to
measure an unknown resistance Rx, when the three other resistances are known.
When the bridge is balanced, no current passes from node a to node b.
i
+
C
v
1
dv/dt
(a)
i
C
-
(b)
Figure 2.12 (a) Capacitor current changes as the derivative of the voltage (b)
Symbol of the capacitor.
+Q
d
-Q
Area = A
Figure 2.13 Diagram of a parallel plate capacitor. The component consists of two
parallel plates of area A separated by a distance d. When charged, the plates carry
equal charges of opposite sign.
C1
C1
C2
C2
(a)
(b)
Figure 2.14 (a) A series combination of two capacitors. (b) A parallel combination
of two capacitors.
V
L
v
1
di/dt
(a)
i
+
L
-
(b)
Figure 2.15 (a) Inductor voltage changes as the derivative of the current. (b)
Symbol of the inductor.
+
i
–10e–5t
L=2H
-
Figure 2.16 Simple inductor circuit.
VC(t)
1
VC(0)
+
+
R
C
-
iC
iR
t
(a)
t
(b)
Figure 2.17 (a) Simple RC circuit with v (0) on capacitor at time t = 0. (b)
Normalized voltage across the capacitor for t  0 (normalized means the largest
value is 1).
+
vR
+
-
VC(t)
I
V
+
V
vC
-
1
VC(t)
-
t
(a)
t
(b)
Figure 2.18 (a) Series RC circuit with voltage step input at time 0. (b) Normalized
voltage across the capacitor.
12
v C (V)
10.8
0.023
0.05
Time (s)
Figure 2.19 Plot of vo for Example 2.8
Amplitude
1
sine
0
T
-1
t
cosine
A = amplitude of sine wave
f = frequency of sine wave in hertz (Hz)
 = angular frequency of sine wave in radians per second
 = phase angle of sine wave in radians
T = 1/f (period in seconds)
Figure 2.20 One period, T, of the sine and cosine waveforms.
y  sin( t )
1
y  sin( 2t )
v (V)
0.5
0
–0.5
–1
0
1
2
3
t (s)
4
5
6
Figure 2.21 Sinusoidal waveforms with different frequencies.
y  sin( t )
1
y  sin( t -  )
v (V)
0.5
0
–0.5
–1
0
1
2
3
t (s)
4
5
6
Figure 2.22 Sinusoidal waveforms with 0º phase angle (solid) and 180º phase angle
(dashed).
Imax
iR
Imax
Vmax
vR
Vmax
Imax
vL
t
iC
Vmax
vC
t
t
iL
(a)
(b)
(c)
Figure 2.23 Plots of the current and voltage as a function of time. (a) With a
resistor both the current and the voltage vary as sin(t), the current is in phase
with the voltage, meaning that when the current is at a maximum, the voltage is
also. (b) For an inductor, the current lags behind the voltage 90. (c) For a
capacitor, the current lead the voltage by 90.
Z1
Ze
Z2
Z1
Z2
(a)
(b)
(c)
Figure 2.24 (a) Series circuit. (b) Parallel circuit. (c) Single impedance equivalent.
RS
v1
vo
+
Rd
-
A(v2 - v1)
v1
-
V+
A
v2
+
vo
V-
v2
(a)
(b)
Figure 2.25 (a) Equivalent circuit for op amp. (b) Symbol of op amp. Many times
V+ and V– are omitted in the op amp symbol, but it is understood that they are
present.
Rf
i
i
-
vi
Ri
A
+
vo
From Ohm’s law:
Figure 2.26 An inverting amplifier. The gain of the circuit is –Rf/Ri
R
Rs
vi
R
vs= 1 V
f
i
A
v
+
Figure 2.27 Inverter circuit attached to a generator that contains an internal
resistance.
o
i
i
Rf
-
-
Ri
A
+
vi
(a)
vo
vi
vo
+
(b)
Figure 2.28 (a) A noninverting amplifier, which also depends on the ratio of the
two resistors. (b) A follower, or buffer, with unity gain.
R
R
i
f
A
Rs
v
o
+
vi
vs= 1 V
Figure 2.29 The gain of the noninverting amplifier is not affected by the addition
of the impedance Rs due to the generator.
R1
R2
v1
R1
v2
-
v3
A
v3
+
R2
Figure 2.30 A differential amplifier uses two active inputs and a common
connection.
vo
R
_
R
R
1
s
+
-
v /2
d
A
+
_
v /2
d
_
v
c
R
+
R
v
o
+
1
s
+
R
+
2
2
Figure 2.31 Differential amplifier attached to a common mode voltage that
contains varying impedances. Adding buffers ensure that fluctuations in Rs does not
affect the gain.
R4 = 1 kW
I
R5 =1.5 kW
4V
R1 = 1 kW
8V
R2 = 500 W
v3
v3
A
+
vo
R3 = 1 kW
Figure 2.32 Differential amplifier for Example 2.13.
R1
Saturated
voltage
vi
vo
-vref = vi
A
vref
+
R2
(a)
vo
vi
(b)
Figure 2.33 (a) A comparator. (b) The input–output characteristic of the
comparator in (a).
R
Threshold
T
P
Q
S
Figure 2.34 Heart beat detector uses a comparator to determine when the R wave
exceeds a threshold.
Gain
Circuit bandwidth
Ideal
gain
Typical open
loop gain
Circuit gain of 10
10
1
100
102
104
Frequency (Hz)
106
Figure 2.35 The typical op amp open loop gain is much larger, but less constant,
than the circuit gain. However the in circuit bandwidth is larger than the open loop
bandwidth.
T(f)
T(f)
PB
PB
1.0
1.0
0.1
0.1
0.01
0.01
1
fc
10
(a)
100
f
1
10
fc
(b)
Figure 2.36 (a) Low-pass filter. (b) High-pass filter.
100
f
T(f)
T(f)
PB
PB
1.0
1.0
0.1
0.1
0.01
0.01
1
f1 10
(c)
f2
100
f
1
PB
f1
10
f2
100
f
(d)
Figure 2.36 (c) Bandpass filter. (d) Bandstop filter. (PB denotes passband)
R
L
(a)
vo
vi
-
-
+
-
+
C
+
+
vi
R
vo
-
(b)
Figure 2.37 Low-pass filter. (a) RC circuit. (b) RL circuit.
R
C
(a)
vo
vi
-
-
+
-
+
R
+
+
vi
L
vo
-
(b)
Figure 2.38 High-pass filter. (a) RC circuit. (b) RL circuit.
Input signal
Low-pass filter
corner frequency
2
High-pass filter
corner frequency
Output
1
Figure 2.39 A low-pass filter and a high-pass filter are cascaded to make a
bandpass filter.
Th
Tl
T
Figure 2.40 A square wave of period T oscillates between two values.
555
+5V
1 Ground
Vcc
8
2 Trigger
Discharge
7
3 Output
Threshold
6
8
4
Ra
7
4 Reset
Control
3
5
Rb
(a)
6
2
5
1
Th = -ln(0.5)(Ra+Rb)C
C
5V
0V
(b)
Tl = -ln(0.5)RbC
(c)
Figure 2.41 The 555 timer (a) Pinout for the 555 timer IC. (b) A popular circuit that utilizes
a 555 timer and four external components creates a square wave with duty cycle > 50%. (c)
The output from the 555 timer circuit shown in (b).
7/8 Vref
Analog output
6/8 Vref
5/8 Vref
4/8 Vref
3/8 Vref
resolution 
2/8 Vref
1
2
1/8 Vref
n
Vref
0V
000
001
010
011
100
101
110
111
Figure 2.42 The ideal static behavior of a 3-bit DAC. For each digital string, there
is a unique analog output.
b2
Vref
R
b1
b0
3-to 8 decoder
7
6
5
4
3
2
1
0
R
R
Vo
R
R
R
R
R
Figure 2.43 A 3-bit voltage scaling DAC converter.
111
110
Digital output
101
100
011
010
001
000
0/8
1/8
2/8
3/8
4/8
5/8
6/8
7/8
Vref
Figure 2.44 Converting characteristic of 3-bit ADC converter.
Clock
Clock
Vin
Digital
control
logic
+
_
Digital
output
DAC converter
Figure 2.45 Block diagram of a typical successive approximation ADC.
Vout
111
110
101
100
1/2 Vref
011
010
001
0
1
111
110
101
100
011
010
001
000
2
3
4
Conversion cycle
Figure 2.46 The possible conversion paths of a 3-bit successive approximation
ADC.
(a)
Amplitude
1
0
-1
0
1
2
3
(b)
Amplitude
1
4
5
6
Time
x[n]  xa (nT )
0
-1
0
5
10
15
20
25
Sample
30 numbers
Figure 2.47 (a) Continuous signal. (b) Sampled sequence of the signal in (a) with
a sampling period of 0.2 s.
Magnitude
(a)
Original
fC
Magnitude
Magnitude
(b)
(c)
Sampling
Sampled
function
signal
Frequency
fS-fC
(d)
Low-pass
filter
(e)
2fSS
2f
Frequency
Frequency
Frequency
Magnitude
fn
Reconstructed
signal
ffSS
Magnitude
fC
fC
Frequency
Figure 2.48 (a) Spectrum of original signal. (b) Spectrum of sampling function. (c) Spectrum of
sampled signal. (d) Low-pass filter for reconstruction. (e) Reconstructed signal, which is the same as
the original signal.
Bus (address, data, control signal)
ROM
RAM
CPU
I/O
Figure 2.49 General block diagram of a microcomputer system (arrows represent
the data flow direction).
Problem
Application software
Editor Complier
Linker
Operating System
CPU
Figure 2.50 Three levels of software separate the hardware of microcomputer
from the real problem.
Cathode
Deflection
control
Screen
Figure 2.51 Sketch for cathode ray tube (CRT). There are two pairs of electrodes to
control the deflection of the electron, but only one pair is shown.