ELECTRONIC CIRCUIT DESIGN 1
402058
Chapter 1
Signals & Amplifiers
ACKNOWLEDGEMENT
This slide is adopted from lecture slides of
Microelectronic Circuits Text by Sedra and Smith,
Oxford Publishing.
Oxford University Publishing
Microelectronic Circuits by Adel S. Sedra and Kenneth C. Smith (0195323033)
13/3/2016
402058 – Chap 1: Signals & Amplifiers
2
INTRODUCTION
IN THIS CHAPTER YOU WILL LEARN…
 That electronic circuits process signals.
 The Thevenin and Norton representations of
signal sources.
 The representation of a signal as sum of sine
waves.
 The analog and digital representations of a
signal.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
3
INTRODUCTION
IN THIS CHAPTER YOU WILL LEARN…
 The signal amplifier.
 How amplifiers are characterized (modeled)
 How the frequency response of an amplifier is
measured and calculated.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
4
1. SIGNALS
 Signal – contains information
 e.g. voice of radio announcer reading the news
 Process – an operation which allows an observer
to understand this information from a signal
 generally done electrically
 Transducer – device which converts signal from
non-electrical to electrical form
 e.g. microphone (sound to electrical)
13/3/2016
402058 – Chap 1: Signals & Amplifiers
5
1. SIGNALS
 Q: How are signals represented?
 A: thevenin form – voltage source vs(t) with
series resistance RS
 preferable when RS is low
 A: norton form – current source is(t) with parallel
resistance RS
 preferable when RS is high
13/3/2016
402058 – Chap 1: Signals & Amplifiers
6
1. SIGNALS
13/3/2016
Two alternative representations of a signal source:
402058 – Chap 1: Signals & Amplifiers
(a) the Thévenin
form; (b) the Norton form.
7
2. FREQUENCY SPECTRUM OF
SIGNALS
 Frequency spectrum – defines a time-domain
signal in terms of the strength of harmonic
components
 Fourier series vs. Fourier transform
13/3/2016
402058 – Chap 1: Signals & Amplifiers
8
WHAT IS A FOURIER SERIES?
 Decomposition – of a periodic function into the
(possibly infinite) sum of simpler oscillating
functions
13/3/2016
402058 – Chap 1: Signals & Amplifiers
9
FOURIER SERIES EXAMPLE
4Va 
1
1
f( x ) 
sin(0t )  sin(30t )  sin(50t ) 

 
3
5
13/3/2016
The frequency spectrum (also known as the line
402058 of
– Chap
& Amplifiers
spectrum)
the1: Signals
periodic
square wave.


10
2. FREQUENCY SPECTRUM OF
SIGNALS
 Q: Can the Fourier Transform be applied to a nonperiodic function of time?
13/3/2016
402058 – Chap 1: Signals & Amplifiers
11
3. ANALOG AND DIGITAL SIGNALS
 Analog signal – is continuous with respect to both
value and time
 Discrete-time signal – is continuous with respect
to value but sampled at discrete points in time
 Digital signal – is quantized (applied to values) as
well as sampled at discrete points in time
13/3/2016
402058 – Chap 1: Signals & Amplifiers
12
3. ANALOG AND DIGITAL SIGNALS
analog signal
discrete-time signal
digital signal
13/3/2016
402058 – Chap 1: Signals & Amplifiers
13
3. ANALOG AND DIGITAL SIGNALS
sampling
quantization
13/3/2016
402058 – Chap 1: Signals & Amplifiers
14
3. ANALOG AND DIGITAL SIGNALS
 Q: Are digital and binary synonymous?
digital
digital and
binary
13/3/2016
402058 – Chap 1: Signals & Amplifiers
15
4. AMPLIFIERS
 Q: Why is signal amplification needed?
 Linearity – is property of an amplifier which
ensures a signal is not “altered” from amplification
 Distortion – is any unintended change in output
13/3/2016
402058 – Chap 1: Signals & Amplifiers
16
4.1. SIGNAL AMPLIFICATION
 Voltage amplifier – is used to boost voltage
levels for increased resolution.
 Power amplifier – is used to boost current levels
for increased “intensity”.
output / input relationship for amplifier
vo (t)  Av vi (t)
voltage gain
13/3/2016
402058 – Chap 1: Signals & Amplifiers
17
4.2. AMPLIFIER CIRCUIT SYMBOL
(a) Circuit symbol for amplifier. (b) An amplifier with a
common terminal (ground) between the input and output
ports.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
18
4.3. POWER AND CURRENT GAIN
 Q: What is one main difference between an
amplifier and transformer? …Because both alter
voltage levels.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
19
4.4. EXPRESSING GAIN IN DECIBELS
 Q: How may gain be expressed in decibels?
13/3/2016
402058 – Chap 1: Signals & Amplifiers
20
5. CIRCUIT MODELS FOR
AMPLIFIERS
 Model – is the description of component’s (e.g.
amplifier) terminal behavior
 neglecting internal operation / transistor design
13/3/2016
402058 – Chap 1: Signals & Amplifiers
21
5.1. VOLTAGE AMPLIFIERS
model of amplifier input terminals
model of amplifier output terminals
Ri
input voltage  vi  (v s )
R  Rs
source i
RL
output voltage  vo  (Avovi )
R  Ro
open-ckt L
volt.
13/3/2016
source and
input
resistances
402058 – Chap 1: Signals & Amplifiers
output
voltage output and
load
resistances
22
5.1. VOLTAGE AMPLIFIERS
 Q: How can one model the amplifier behavior
from previous slide?
 A: Model which is function of: vs, Avo, Ri, Rs,
Ro, RL






R
RL
Ri
RL
i


vo  Avo (v s )
 Avov s
 source Ri  Rs  RL  Ro
Ri  Rs RL  Ro


volt.
source and output and
input

 load
resistances

 resistances
13/3/2016
open-ckt output
voltage
402058
– Chap 1: Signals & Amplifiers
23
5.1. VOLTAGE AMPLIFIERS
 Q: What is one “problem” with this behavior?
 A: Gain (ratio of vo and vs) is not constant,
and dependent on input and load resistance.






R
RL
i
 RL  Avov s Ri
vo   Avo (v s )
 source Ri  Rs  RL  Ro
Ri  Rs RL  Ro


volt.
source and output and
input

 load
resistances  resistances

output
voltage
402058
– Chap 1: Signals
& Amplifiers
The ideal open-ckt
amplifier
model
neglects
this nonlinearity. 24
13/3/2016
5.1. VOLTAGE AMPLIFIERS
 Ideal amplifier model – is function of vs and Avo
only!!
 It is assumed that Ro << RL…
 It is assumed that Ri << Rs…
non-ideal model
ideal model
key characteristics of ideal voltage amplifier model = high input
25
13/3/2016
402058 – Chap
Signals & impedance
Amplifiers
impedance,
low1:output
5.1. VOLTAGE AMPLIFIERS
 Ideal amplifier model – is function of vs and Avo
only!!
 It is assumed that Ro << RL…
 It is assumed that Ri << Rs…
Ri
RL
vo  Avov s
 Avov s
Ri  Rs RL  Ro ideal
non-ideal model
model
key characteristics of ideal voltage amplifier model = source
26
13/3/2016resistance R and 402058
Chap 1: SignalsR& Amplifiers
load –resistance
S
L have no effect on gain
5.2. CASCADED AMPLIFIERS
 In real life, an amplifier is not ideal and will not have
infinite input impedance or zero output impedance.
 Cascading of amplifiers, however, may be used to
emphasize desirable characteristics.
 first amplifier – high Ri, medium Ro
 last amplifier – medium Ri, low Ro
 aggregate – high Ri, low Ro
13/3/2016
402058 – Chap 1: Signals & Amplifiers
27
EXAMPLE 1.3: CASCADED
AMPLIFIER CONFIGURATIONS
 Examine system of cascaded amplifiers on next
slide.
 Q(a): What is overall voltage gain?
 Q(b): What is overall current gain?
 Q(c): What is overall power gain?
13/3/2016
402058 – Chap 1: Signals & Amplifiers
28
EXAMPLE 1.3: CASCADED
AMPLIFIER CONFIGURATIONS
Three-stage amplifier for Example 1.3.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
29
5.3. OTHER AMPLIFIER TYPES
voltage amplifier
current amplifier
transconductance amp.
transresistance amp.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
30
5.3. OTHER AMPLIFIER TYPES
v0
Av 0 
vi
with
i0 0
Ri  
Ro  0
i0
Av 0 
ii
with
v0 0
voltage amplifier
transconductance amplifier
i0
Gm 
13/3/2016 vi
Ri  0
Ro  
current amplifier
transresistance amplifier
Ri  
v0 0
Ri  0
v0
with
Rm 
with
Ro – 
Ro  0
ii i 0
402058
Chap 1: Signals & Amplifiers
31
0
5.4. RELATIONSHIP
BETWEEN FOUR AMP MODELS
 Interchangeability – although these four types
exist, any of the four may be used to model any
amplifier
 They are related through Avo (open circuit gain)
current
to voltage
amplifier
transcond.
to voltage
amplifier
transres.
to voltage
amplifier
 Ro 
Rm
Avo  Ais    GmRo 
Ri
 Ri 
13/3/2016
402058 – Chap 1: Signals & Amplifiers
32
5.5. DETERMINING RI AND RO
 Q: How can one calculate input resistance from
terminal behavior?
 A: Observe vi and ii, calculate via Ri = vi / ii
 Q: How can one calculate output resistance from
terminal behavior?
 A:
 Remove source voltage (such that vi = ii = 0)
 Apply voltage to output (vx)
 Measure negative output current (-io)
33
R–oChap
= -v
13/3/2016  Calculate via
402058
1: Signals
x / io& Amplifiers
Section 1.5.5:
Determining Ri and Ro
 question: how can we calculate input resistance from terminal behavior?
 answer: observe vi and ii, calculate via Ri = vi / ii
 question: how can we calculate output resistance from terminal
behavior?
 answer:




remove source voltage (such that vi = ii = 0)
apply voltage to output (vx)
measure negative output current (-io)
calculate via Ro = -vx / io
Determining the output resistance.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
34
5.6. UNILATERAL MODELS
 Unilateral model – is one in which signal flows only
from input to output (not reverse)
 However, most practical amplifiers will exhibit
some reverse transmission…
13/3/2016
402058 – Chap 1: Signals & Amplifiers
35
EXAMPLE 1.4: COMMON-EMITTER
CIRCUIT
 Examine the bipolar junction transistor (BJT).
 three-terminal device
 when powered up with dc source and operated
with small signals, may be modeled by linear
circuit below.
C
B
E
13/3/2016
402058 – Chap 1: Signals & Amplifiers
36
base
input resistance (r)
Example 1.4.
output resistance (ro)
collector
 examine:
 bipolar junction transistor (BJT):
 three-terminal device
 when powered up with dc source and operated with small signals,
may be modeled by linear circuit below.
short-circuit
conductance
13/3/2016 (g )
m
emitter
small-signal circuit model for
a bipolar junction transistor
(BJT)
402058 – Chap 1: Signals & Amplifiers
37
EXAMPLE 1.4: COMMON-EMITTER
CIRCUIT
 Q(a): Derive an expression for the voltage gain vo /
vi of common-emitter circuit with:
 Rs = 5kohm
 r = 2.5kohm
 gm = 40mA/V
 ro = 100kohm
 RL = 5kohm
13/3/2016
402058 – Chap 1: Signals & Amplifiers
38
input and output share common terminal
source
load
The BJT connected as an amplifier with the emitter as
a common terminal between input and output (called a
39
13/3/2016
402058 – Chap 1: Signals & Amplifiers
common-emitter
amplifier).
6. FREQUENCY RESPONSE OF
AMPLIFIERS
 Reading assignment:
Section 1.6 pg 33-43
Sedra/Smith, Microelectronic Circuits, 7e.
13/3/2016
402058 – Chap 1: Signals & Amplifiers
40
SUMMARY
IN THIS CHAPTER, YOU HAVE LEARNED:
 the Thevenin and Norton representations of
signal sources
 the representation of a signal
 the signal amplifier and its characteristics
 the frequency response of an amplifier
13/3/2016
402058 – Chap 1: Signals & Amplifiers
41
HOMEWORK
Sedra/Smith, Microelectronic Circuits, 7e.
Chapter 1 problems:
1.2, 1.5 ,1.6
1.10, 1.14, 1.15
1.16, 1.17, 1.18, 1.19
1.20, 1.39, 1.43, 1.63
Prepare Chapter 4: Diodes
13/3/2016
402058 – Chap 1: Signals & Amplifiers
42