1  

6.002x CIRCUITS AND ELECTRONICS

Introduction and Lumped Circuit Abstraction

2  

6.002x is Exciting!

What’s behind this?

3  

…and this

Chip photo of Intel’s 22nm multicore processor codenamed Ivy Bridge

Photograph  courtesy  of  Intel  Corp.  

4  

n  Prerequisites

n  AP level course on electricity and magnetism; e.g., MIT’s 8.02 (check it out on MIT OpenCourseware)

n  It is also useful to have a basic knowledge of solving simple differential equations

n  Textbook Agarwal and Lang (A&L) Underlined readings (in course-at-a-glance handout) are very important as they stress intuition

n  Weekly homeworks and labs must be completed by the deadline indicated on the assignment

n  Assessments

ADMINISTRIVIA

Homeworks 15% Labs 15% 1 Midterm 30% Final exam 40%

5  

What is engineering?

What is 6.002x about?

Purposeful use of science

Gainful employment of Maxwell’s equations From electrons to digital gates and op-amps

6  

Sim

ple

ampl

ifie

r ab

stra

ctio

n

Inst

ruct

ion

set

abst

ract

ion

Pent

ium

, MIP

S

Soft

ware

sys

tem

s O

pera

ting

sy

stem

s, B

rows

ers

Filt

ers

Ope

rati

onal

am

plif

ier

abst

r.

-+"

Dig

ital

abs

trac

tion

Prog

ram

min

g la

ngua

ges

Java

, C++

, Mat

lab,

Pyt

hon

Com

bina

tion

al lo

gic

f

Lum

ped

circ

uit

abst

ract

ion

6.002x

Nat

ure

as o

bser

ved

in e

xper

imen

ts

Phys

ics

laws

or

“abs

trac

tion

s”

l

Max

well’

s l

Ohm

’s

V

= R

I

abst

ract

ion

for

tabl

es o

f da

ta

Cloc

ked

digi

tal a

bstr

acti

on

Ana

log

sub

syst

ems

Mod

ulat

ors,

os

cilla

tors

, RF

am

ps,

po

wer

supp

lies

Mic

e, t

oast

ers,

son

ar, s

tere

os, a

ngry

bir

ds,

spac

e sh

uttl

e, iP

AD

6.

172,

6.17

3 6.

455

+ –"

R

C

L

M

S

V  

6.06

1

6.00

4, 6

.846

 

6.00

6.03

3

7  

Consider

V

Suppose we wish to answer this question: What is the current through the bulb?

The Big Jump from physics

to EECS

Lumped Element Abstraction

Reading: Skim through Chapter 1 of A&L

8  

Apply Maxwell’s

Faraday’s

Continuity

Others

tBE∂∂

−=×∇

tJ

∂∂

−=⋅∇ρ

0

Eερ

=⋅∇l l l

tdlE B

∂∂

−=⋅∫φ

tqdSJ∂∂

−=⋅∫

0εqdSE =⋅∫

l l l

We could do it the Hard Way…

Integral form Differential form

V

I ?  

9  

Instead, there is an Easy Way… First, let us build some insight: Analogy

I ask you: What is the acceleration? You quickly ask me: What is the mass?

I tell you:

You respond:

Done ! ! !

10  

Instead, there is an Easy Way…

In doing so, you ignored l the object’s shape l its temperature l its color l  point of force application l  …

Point-mass discretization

F a?

11  

The Easy Way… Consider the filament of the light bulb.

We do not care about l how current flows inside the filament l its temperature, shape, orientation, etc.

A

B

We can replace the bulb with a discrete resistor for the purpose of calculating the current.

12  

The Easy Way…

Replace the bulb with a discrete resistor for the purpose of calculating the current.

A

B

13  

The Easy Way…

R represents the only property of interest! Like with point-mass: replace objects with their mass m to find

mFa =

In EECS, we do things the easy way…

A

B

A

B

R

I + – V R

VI =

14  

RVI =

V-I Relationship

R represents the only property of interest!

and RVI =

relates element V and I R

called element v-i relationship

A

B

R

I + – V

15  

R is a lumped element abstraction for the bulb.

16  

16  

Lumped circuit element described by its vi relation

Power consumed by element = vi

Lumped Elements

+  

-­‐  

Voltage source  

+"–"V i

v

i

v

+  

-­‐  

Resistor  i

v

i

v

17  

Lumped element examples whose behavior is completely captured by their V–I relationship.

Demo only for the sorts of questions we as EEs would like to ask!

Exploding resistor demo can’t predict that! Pickle demo can’t predict light, smell

Demo

18  

Not so fast, though … A

B Bulb filament

Although we will take the easy way using lumped abstractions for the rest of this course, we must make sure (at least for the first time) that our abstraction is reasonable.

are defined for the element V I In this case, ensuring that

19  

A

B

black box

I +

–

I must be defined.

V

20  

I

I into = I out of

True only when in the filament! 0=∂∂tq

AImust be defined. True when

BA II = only if 0=∂∂tq

We’re engineers! So, let’s make it true!

So, are we stuck?

BI

AS BS

AS

BS

21  

V

defined when ABV 0=∂∂tBφ

outside elements dlEVABAB ⋅= ∫

see A & L Appendix A.1

Must also be defined.

So let’s assume this too!

So

Also, signal speeds of interest should be way lower than speed of light

A

B

I +

–

V

22  

Welcome to the EECS Playground The world

The EECS playground Our self imposed constraints in this playground

0=∂∂tBφ Outside

0=∂∂tq Inside elements

Bulb, wire, battery

Where good things happen

23  

Connecting using ideal wires lumped elements that obey LMD to form an assembly results in the lumped circuit abstraction

Lumped Matter Discipline (LMD)

0=∂∂tBφ outside

0=∂∂tq inside elements

bulb, wire, battery

Or self imposed constraints:

More in Chapter 1 of A & L

24  

Replace the differential equations with simple algebra using lumped circuit abstraction (LCA).

What can we say about voltages in a loop under the lumped matter discipline?

+"–"1R

2R

4R

5R

3R

a

b d

c

V

So, what does LMD buy us?

For example:  

Reading: Chapter 2.1 – 2.2.2 of A&L

25  

What can we say about voltages in a loop under LMD?

Kirchhoff’s Voltage Law (KVL): The sum of the voltages in a loop is 0.

Remember, this is not true everywhere, only in our EECS playground

+"–"1R

2R

4R

5R

3R

a

b d

c

V

26  

What can we say about currents?

+"–"

1R

2R

4R

5R

3R

a

b d

c

V

27  

aWhat can we say about currents? S

caI daI

baI

Kirchhoff’s Current Law (KCL): The sum of the currents into a node is 0.

simply conservation of charge

28  

KVL:

KCL:

KVL and KCL Summary

29  

29  

Remember, our EECS playground

0=∂

∂

tBφ

0=∂

∂

tq

Outside elements

Inside elements

Allows us to create the lumped circuit abstraction

wires resistors sources

Summary Lumped Matter Discipline LMD: Constraints we impose on ourselves to simplify our analysis

Also, signals speeds of interest should be way lower than speed of light

30  

30  

Lumped circuit element +  

-­‐  

v

i

power consumed by element =    vi

Summary

31  

31  

KVL:

loop KCL:

node

0=∑ j jν

0=∑ j ji

Review Summary

Maxwell’s equations simplify to algebraic KVL and KCL under LMD.

This is amazing!