ELEC 101
AC Circuits 1
2009/10 Spring
Sinusoidal (AC) Circuits
1
Basics
A
Sinusoids are important
AC has advantages over DC for simple
transmission and low transmission loss.
1. Most signals are sinusoids (sine/cosine waves)
2. Sinusoids are building bloc
(34)
10
In the ideal op amp circuit below,
(a) find the complex transfer function G = Vo/Vi in terms of Z1
and Z2 .
(b) If the circuit is a high pass filter, find Z1 and Z2 in terms of R1,
R2 and C and sketch the circuit. (8)
(c) Find the complex transfer
(16)
2
Find VO / VS in terms of R, C and jw. If C = 1F , R1 = 1k, R2
= 10k, find the complex transfer function G (= VO / VS ). Is the
op amp circuit a low pass filter? Assume the op amp is ideal.
(16)
R1
C
R1
VS
R2
VO
VO
R2
= 1+
1
VS
R1 +
jC
1
1
R
R
= 1+
2 VDD 8V Given VT =1V K = 0.25mA/V2 2k 3.5V RD VD VS IDS
Find VDS and IDS for VG = 3.5V
MOS is in saturation mode
I DS = K (VGS  VT ) 2 = 0.25m(3.5  1) 2 = 1.5625mA
VDS = VDD  I DS R D = 8  (1.5625m )2k 4.875V
I DS = 8  4.875 = 1.5625mA 2k
(19) 4
(270)
(34)
1
(a) Show that the resistivity of intrinsic (pure) silicon (Si) is 2278 m.
(b) A silicon is doped with Indium (group 3) atoms to 0.026 m,
find the type of silicon (ntype Si or ntype Si). Find also the
indium atoms concentrations required. H
Example 1: (From Ex1.24, Electric Circuits, 5th Ed. Nilsson/Riedel)
a) In the circuit shown in Fig. 1, identify which elements have the voltage current
reference polarities defined using the passive sign convention.
b) The numerical values of the for each
Example 1: (From D2.10 Introduction to Electrical Engineering by Irwin)
Find the equivalent resistance at the terminal AB in Fig 1.
A
Fig. 1
6
2
1
RAB
2
6
1
2
B
Answers to Example 1:
A
Combining the 2 and 1 resistors on the right
and the two 2 resistors
Example 1: (From 2.33, Introduction to Electrical Engineering by Irwin)
Computer Vo in the network in Fig. 1
6
4
+
4
Fig. 1
8 Vo
36V
48V

Answers to Example 1:
4
4
+
+
4
6A
6
8 Vo
6 4 12A
6A
8 Vo
48V

2.4
14.4V
4

8 Vo

Vo = 14.4
8
= 8V
2.4 + 4 + 8
Example 1: (From P57, Circuits, Devices and Systems by Smith and Dorf)
Given the circuit of Fig. 1, determine the impedance presented to:
(a) A direct current i = I = 20mA
i
(b) A sinusoidal current
+
i = 20 2cos(5000t + 60)mA
L=1H
Fig. 1
C=0.25 VC
F
V
A
Department of Electronic & Computer Engineering
THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY
ELEC101 BASIC ELECTRONICS
Homework #2
(This Homework is not required to submit)
1. (3.32) Find i0(t) for t>0 in Figure P3.32.
2. (3.38) In the circuit shown
ELEC 101
18
Transient Circuits 25
Bistable Circuit
2009/10 Spring
Schmitt trigger
R1
Bistable circuit has two stable states.
R2
A positivefeedback loop can generate a
bistable circuit.
R1
V
VI
R2
V
+Vsupply
V
VO
V
VO
Vsupply
+Vsupply
VO
VTL
VTH
0
VO stab
ELEC 101
Transient Circuits 1
2009/10 Spring
Transient Circuit
Example
Study the behavior of a network as a function of
time after a sudden change in the network occurs
due to the switches opening and closing.
Example
switch opens at t = 0
iL
t=0
2k
You h
ELEC 101
1
Basic Elements 1
2009/10 Spring
Fundamental
Multiplier for prefix will be
given in tests and exam
Derived from Basic Quantities
1021 zepto (z)
1024 yocto (y)
1015
1018
1021
1024
peta (P)
exa (E)
zetta (Z)
yotta (Y)
Can use the unit to check
equ
ELEC 101
Bipolar Transistor 1
2009/10 Spring
Bipolar Transistor (BJT)
1
A Short History of Transistor
1945  Transistors as amplifiers
William Bradford Shockley, John Bardeen ,
Walter Houser Brattain in Bell Telephone
Laboratories
The three of them won th
ELEC 101
DC Circuits 1
DC Circuits
1
Basic Definitions
A
Circuit diagram
is a graphical representation of a circuit
(closed connection of elements).
Node a (wire, or
contains no element)
Example
+ v1
Branch
voltage
Node b
R1
Node c
i4
Branch
current
R2
R
ELEC 101
DC Circuits 1
DC Circuits
1
Basic Definitions
A
Circuit diagram
is a graphical representation of a circuit
(closed connection of elements).
Node a (wire, or
contains no element)
Example
+ v1
Branch
voltage
Node b
R1
Node c
i4
Branch
current
R2
R
ELEC 101
1
Diode Circuits 1
Diode (or PN junction diode)
First nonlinear circuit element
b
2009/10 Spring
ID  VD Curve
(or ID  VD Characteristics)
VD
Twoterminals passive element with
nonlinear IV characteristics.
ID
ID
VD < 0
a
Reverse
breakdown
reg
ELEC 101
A
Signals and Instruments 1
Basics in signals
f(t)
b
t
Signals contain information about a variety
of things and activities in our physical
world.
Periodic Waveforms
A waveform v(t) is periodic with period T if
v(t) = v(t + nT)
Square Wave
Vm
0
V
ELEC 101
1
Op Amp Circuits 1
2009/10 Spring
Voltage Amplifier
also called VoltageControlled VoltageAmplifier or VtoV converter
a Circuit Model of voltage amplifier
Vi
RO
Ri
VO
AVVi
Vi : input voltage
VO : output voltage
Ri : input resistance
RO : outpu
ELEC 101
Semiconductor 1
1
Conductor and Insulator
a
Conductor
The outer shells of most metal atoms are
partially filled. Hence the outer electrons
are loosely bounded and can easily escape
from the metal atoms.
b
+

+
+
+
+


+


+


+
+
+
+


+
Example 1: (From P117, Circuits, Devices & Systems, by R.J. Smith and R.C. Dorf)
It is desired to increase the conductivity of silicon by a factor of 1000 by doping with
arsenic (Group V) element. Specify the doping density and identify the important cha