Review Outline 1 1. Chapter 1: Signals and Amplifiers 2 ...faculty.weber.edu/snaik/EE3110/02Midterm_Review.pdf · Chapter 3: Semiconductors 3. Chapter 4: Diodes. ... Chapter 1: Signals

EE 3110 Microelectronics I Suketu Naik

1Review Outline

1. Chapter 1: Signals and Amplifiers

2. Chapter 3: Semiconductors

3. Chapter 4: Diodes


21.1 Signals

Signal – contains information

e.g. voice of radio announcer reading the news

Transducer – device which converts signalfrom non-electrical to electrical form

e.g. microphone (sound to electrical)

Process – an operation which allows an observer to understand this information from a signal

generally done electrically


31.4 Amplifiers

Q: Why is signal amplification needed?

A: Because many transducers yield output at low power

levels (mW or nW)

Linearity – is property of an amplifier which ensures a

signal is not “altered” from amplification

Distortion – is any unintended change in output


41.5.1 Voltage Amplifiers

model of amplifier input terminals

sourcevolt.

source andinput

resistances

input vo tag )l e ( ii s

i s

Rv v

R R

model of amplifier output terminals

open-cktoutput

output andvoltageload

resistances

output vo (l )tage Lo vo i

L o

Rv A v

R R

Figure 1.16 (b): voltage amplifier with input signal source


51.5.1 Voltage Amplifiers

Ideal amplifier model – is function of vs and Avo only!!

It is assumed that Ro << RL…

It is assumed that Ri >> Rs…

idealmodel

non-ideal model

i Lo vo s vo s

i s L o

R Rv A v A v

R R R R

Key characteristics of ideal voltage amplifier model

1) Source resistance RS and load resistance RL have no effect on gain

2) High input resistance Ri (>>RS) and low output resistance Ro(<<RL)


6Example 1.3: Cascaded Amplifier Configurations

Figure 1.17: Three-stage amplifier for Example 1.3.

• High Input

Resistance

• Modest

Gain

• Low Input

Resistance

• High Gain

• Low

Output

Resistance

• Unity Gain


7Review Outline





8

Valence electron – is an electron that participates in the formation of chemical bonds.

Lies in the outermost electron shell of an element

The number of valence electrons that an atom has determines the kinds of chemical bonds that it can form.

Covalent bond – is a form of chemical bond in which two atoms share a pair of electrons

By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability

3.1. Intrinsic Semiconductors

valence

electron

covalent

bond


93.2 Doped Semiconductors

p-type semiconductor

doped with trivalent

impurity atom

(e.g. Boron)

n-type semiconductor

doped with pentavalent impurity atom (e.g. Phosphorus)


103.3 Current Flow in Semiconductors

Summary

Holes (absence of electrons, p) and free electrons (n):

p-type semiconductor: holes are majority carriers ( pp ),

free electrons (np) are minority carriers

n-type semiconductor: free electrons are majority

carriers (nn), holes are minority carriers ( pn )

Two distinct mechanisms for current flow (movement

of charge carriers)

Drift Current (IS)

Diffusion Current (ID)


11Mobility

Holes have less mobility than free electrons

Why?

Free electrons are loosely tied to the nucleus and are closer

to the conduction band (higher orbits, see slide 19)

Holes are absence of electrons in the covalent bond

between Si atoms and B

Holes are locked or subjected to the stronger atomic force

pulled by the nucleus than the electrons residing in the

higher shells or farther shells

So, holes have a lower mobility


123.4.1 Physical Structure

pn junction (diode) structure

p-type semiconductor

n-type semiconductor

metal contact for connection


13pn junction: modes of operation

(a) Open-circuit:voltage drop across depletion region = V0 , ID = IS

(b) Reverse bias:voltage drop across depletion region = V0 +VR, ID < IS

(c) Forward bias:voltage drop across depletion region = V0 -VF, ID > IS


14Reverse-Bias Case

Observe that increased barriervoltage will be accompanied by…

(1) Increase in stored uncovered charge on both sides of junction

(2) wider depletion region

pp

p0p

0

0

width of depletion region

electrical permiability of silicon (11.7 1.04 12 )

magn

replace with

itude of electron ch

/

0

arge

P

P

(eq3.31)2 1 1

( )

S

R

F cm

Sn p R

VV V

W

q

A D

W x x V Vq N N

action:

Epp

pp

pp

p0 p

pp

concentration of acceptor atoms

concentration of donor atoms

barrier / junction built-in voltage

externally applied reverse-bias volta

P

P

P

g Pe

P

(eq3.3 22)

A

D

R

N

N

V

J

V

Q A

0

pp

0

magnitude of charge store

0

d on either side of depletion re

replace with

gi Pon

( )

J

R

VV V

A DS R

A

Q

D

N Nq V V

N N

action:


15

Observe that decreased barrier voltage will be accompanied by

(1) Decrease in stored uncovered charge on both sides of junction

(2) Smaller depletion region

0

0

pp

pp

pp

0

width of depletion region

electrical permiability of silicon (11.7 1.04 12 )

magnitude of electron charge

con

replac

P

P

P

/

e with

0

2 1 1( )

A

F

S F c

V

W

q

m

Sn p F

A D

N

V V

W x x V Vq N N

action:

E

pp

pp

pp0

pp

centration of acceptor atoms

concentration of donor atoms

barrier / junction built-in voltage

externally applied forward-bias voltage

P

P

P

0

P

2 (

D

F

A DJ S F

A D

N

V

V

N NQ A q V V

N N

0

pp

0

magnitude of charge stored on either side of

rep

dep

lace wit

letion region

P

h

)

J

FV V

Q

V

action:

Forward-Bias Case


16Review Outline





174.1 The Ideal Diode

Ideal diode – most fundament nonlinear circuit element

Operates in two modes:

Off (reverse biased, (c)), On (forward biased, (d))

Off (Reverse Biased)

Open Circuit

On (Forward Biased)

Short Circuit

On Off p type n type


184.3.5 Constant Voltage-Drop Model

The constant voltage-drop diode modelassumes that the slope of ID vs. VD is vertical @ 0.7V

Negligible difference between values obtained from the exponential model (most accurate)

Example


194.3.1 Exponential Model:

Q: How does one solve

for ID in circuit to right?

A:

Graphical method

Iterative methodTD VV

SD

DDDD

eII

R

VVI

/

eq 4.6

eq 4.7

TD VV

SD eII/


20Terminal Characteristics of Junction Diodes

I-V curve

consists of three

characteristic

regions

forward bias:

v > 0

reverse bias:

v < 0

breakdown:

v << 0


21Exercise 4.4

Find I and V using

(a) Ideal diode model (b) Constant voltage drop model

Ans: 4.4 (a) 2 mA, 0V (c) 0 mA, -5V

4.4


22

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P4.3


23Examples and Excercises

Example 1:

VDD = 5 V

R = 1 kΩ

ID = 1 mA @ 0.7 V

Model

Type/

Parameter

Ideal diode

model

Constant

voltage-drop

model

Exponential

Model: Iterative

Method

VD 0 V 0.7 V0.738 V (2nd

iteration)

ID 5 mA 4.3mA4.262 mA (2nd

iteration)

Excercises

D4.11, 4.12 (a)


244.3.1 Exponential Model:

Q: How does one solve

for ID in circuit to right?

A:

Graphical method

Iterative methodTD VV

SD

DDDD

eII

R

VVI

/

eq 4.6

eq 4.7

TD VV

SD eII/


254.3.7 Small Signal Model

DC analysis: Use constant voltage drop model

AC analysis: Use resistor as diode

Notation:

DC only – upper-case w/ upper-case

subscript, VD

Time-varying only – lower-case w/

lower-case subscript, vd

total instantaneous – lower-case w/

upper-case subscript, vD

DC

AC (time

varying)



Substitute eq.4.9 in eq.4.10

Split this exponential

Redefine total instant current in

terms of DC component (ID)

and time-varying voltage (vd)

Apply power series expansion

to (4.12) and keep upto first

order terms

)()(

)(

/

tvVtv

eII

V

vIti

dDD

VV

sD

T

dDD

TD

1

d

(eq4.14

)

(eq4.8)

(eq4.9)



Small signal approximation

total instant current (iD)

small-signal current (id.)

small-signal resistance (rd.)

accurate for vd < 5mV amplitude (not peak to peak)

somewhat accurate for vd > 5mV

( )

( )

1

d

DD D d

T

D D d

d d

d

Td

D

i

Ii t I v

V

i t I i

i vr

Vr

I

(eq4.14

)


28Example 4.5

V+ = 10 V with 1 V peak amp at

60 Hz (power supply ripple)

R = 10 kΩ

ID = 1 mA @ 0.7 V

Calculate dc voltage and the

amplitude of ac signal across

the diode.


294.4 Zener Diodes

ZZZOZ IrVV

VZK ≈ VZO

We will revisit Zener diode in

section 4.6 (limiter circuit)


304.1.2 Application: Rectifier

Rectifier converts

ac signal in to dc

signal

During positive

cycle, current will

flow through the

diode (forward

biased)

During negative

cycle, no current

will flow through

the diode (reverse

biased)

Off On

Off

On On


31Half Wave Rectifier with a Filter Capacitor


32Full-Wave Rectifier

Center-tapping of the transformer, allowing “reversal”

of certain currents…


33Bridge Rectifier

Documents

Review Outline 1 1. Chapter 1: Signals and Amplifiers 2 ...faculty.weber.edu/snaik/EE3110/02Midterm_Review.pdf · Chapter 3: Semiconductors 3. Chapter 4: Diodes. ... Chapter 1: Signals