
2/43

Announcements

HW1 due NOW

Lab1 tomorrow in ZACH 203

Prelab 1 due tomorrow

Reference Material Posted on Website

TDR theory application note

S-parameter notes

2


3/43

Agenda

Channel Components IC Packages, PCBs, connectors, vias, PCB Traces

Wire Models

Resistance, capacitance, inductance

Transmission Lines

Propagation constant

Characteristic impedance

Loss Reflections

Termination examples

Differential transmission lines

3


4/43

Channel Components

4

Edge connector

Packaged SerDes

Line card trace

Backplane trace

Via stub

The ChannelTx IC

Pkg Line cardtrace

Edgeconnector

Line cardvia

Backplanevia

Backplane16 trace

Edgeconnector

Line cardtrace

Rx IC

Pkg Backplanevia

Line cardvia

[Meghelli (IBM) ISSCC 2006]


5/43

IC Packages

Package style dependson application and pincount

Packaging technologyhasnt been able toincrease pin count atsame rate as on-chipaggregate bandwidth

Leads to I/O constraineddesigns and higher datarate per pin

5

Package Type Pin Count

Small Outline Package (SOP) 8 56

Quad Flat Package (QFP) 64 - 304

Plastic Ball Grid Array (PBGA) 256 - 420

Enhanced Ball Grid Array (EBGA) 352 - 896

Flip Chip Ball Grid Array (FC-BGA) 1089 - 2116

SOP

PBGA

QFP

FC-BGA

[Package Images - Fujitsu]


6/43

IC Package Examples

Wirebonding is mostcommon die attach method

Flip-chip packaging allows

for more efficient heatremoval

2D solder ball array onchip allows for moresignals and lower signaland supply impedance

6

Standard Wirebond Package

Flip-Chip/Wirebond Package

Flip-Chip/Solder Ball Package

[Package Images - Fujitsu]


7/43

IC Package Model

7

BondwiresL ~ 1nH/mmMutual L KCcouple

~20fF/mm

Package TraceL ~ 0.7-1nH/mmMutual L KClayer

~80-90fF/mmC

couple

~40fF/mm

[Dally]


8/43

Printed Circuit Boards

Components soldered ontop (and bottom)

Typical boards have 4-8signal layers and anequal number of powerand ground planes

Backplanes can haveover 30 layers

8


9/43

PCB Stackup

Signals typically on top andbottom layers

GND/Power plane pairs and

signal layer pairs alternate inboard interior

Typical copper trace thickness

0.5oz (17.5um) for signal layers 1oz (35um) for power planes

9

[Dally]


10/43

Connectors

Connectors are usedto transfer signalsfrom board-to-board

Typical differentialpair density between

16-32 pairs/10mm

10

[Tyco]


11/43

Connectors

Important to maintain proper differentialimpedance through connector

11

Crosstalk can be an issue in the connectors

[Tyco]


12/43

Vias

Used to connect PCB layers

Made by drilling a hole throughthe board which is plated with

copper Pads connect to signal layers/traces

Clearance holes avoid power planes

Expensive in terms of signaldensity and integrity

Consume multiple trace tracks

Typically lower impedance and createstubs

12

[Dally]


13/43

Impact of Via Stubs at Connectors

13

Legacy BPhas default straight vias

Creates severe nulls which kills signal integrity

Refined BP has expensive backdrilled vias

Edge connector

Packaged SerDes

Line card trace

Backplane trace

Via stub


14/43

PCB Trace Configurations

Microstrips are signaltraces on PCB outersurfaces

Trace is not enclosed

and susceptible tocross-talk

Striplines aresandwiched between

two parallel groundplanes

Has increased isolation

14

[Johnson]


15/43

Wire Models

Resistance

Capacitance

Inductance

Transmission line theory

15


16/43

Wire Resistance

Wire resistance is determined by materialresistivity, , and geometry

Causes signal loss and propagation delay

16

wh

l

A

lR

==

2r

l

A

lR

==

[Dally]


17/43

Wire Capacitance

Wire capacitance is determinedby dielectric permittivity, ,

and geometry

Best to use lowest r

Lower capacitance

Higher propagation velocity

17

s

wC

=

( )12

log

2

rrC

=

( )rsC

log

=

( )hssw

C4log

2+=

[Dally]


18/43

Wire Inductance

Wire inductance is determined by materialpermeability, , and closed-loop geometry

For wire in homogeneous medium

Generally

18

=CL

H/m104 70 ==


19/43

Wire Models

Model Types Ideal

Lumped C, R, L

RC transmission line

LC transmission line

RLGC transmission line

Condition for LC or RLGC model (vs RC)

19

L

Rf

20

Wire R L C >f (LC wire)

AWG24 Twisted Pair 0.08/m 400nH/m 40pF/m 32kHz

PCB Trace 5/m 300nH/m 100pF/m 2.7MHz

On-Chip Min. Width M6(0.18m CMOS node)

40k/m 4H/m 300pF/m 1.6GHz


20/43

RLGC Transmission Line Model

20

( ) ( ) ( )ttxILtxRI

xtxV

=

,,,

( )( )

( )t

txVCtxGV

x

txI

=

,,

,

0dxAs (1)

(2)

GeneralTransmissionLine Equations


21/43

Time-Harmonic Transmission Line Eqs.

Assuming a traveling sinusoidal wave with angular frequency,

21

( )( ) ( )xILjR

dx

xdV+=

( )( ) ( )xVCjG

dx

xdI+=

Differentiating (3) and plugging in (4) (and vice versa)

( )( )xV

dx

xVd 22

2

=

( ) ( )xIdx

xId 22

2=

where is the propagation constant

( )( ) ( )-1mCjGLjRj ++=+=

(5)

(6)

Time-HarmonicTransmission

Line Equations

(3)

(4)


22/43

Transmission Line Propagation Constant

Solutions to the Time-Harmonic Line Equations:

22

( ) ( ) ( ) xrx

frf eVeVxVxVxV

00 +=+=

What does the propagation constant tell us?

Real part () determines attenuation/distance (Np/m) Imaginary part () determines phase shift/distance (rad/m)

Signal phase velocity

( ) ( ) ( ) xrx

frf eIeIxIxIxI

00 +=+=

where ( )( ) ( )-1mCjGLjRj ++=+=

(m/s)=


23/43

Transmission Line Impedance, Z0

For an infinitely long line, the voltage/current ratio is Z0 From time-harmonic transmission line eqs. (3) and (4)

23

( )

( ) ( )

+

+==

0 CjG

LjR

xI

xVZ

Driving a line terminated by Z0 is the same as driving aninfinitely long line

[Dally]


24/43

Lossless LC Transmission Lines

If Rdx=Gdx=0

24

LC

LCjj

=

=

=+=

0

C

LZ

LC

=

==

0

1

No Loss!

Waves propagate w/o distortion Velocity and impedance

independent of frequency

Impedance is purely real

[Johnson]


25/43

Low-Loss LRC Transmission Lines

If R/L and G/C


26/43

Skin Effect (Resistive Loss)

High-frequency current density fallsoff exponentially from conductorsurface

Skin depth, , is where current fallsby e-1relative to full conductor

Decreases proportional tosqrt(frequency)

Relevant at critical frequency fswhere skin depth equals half

conductor height (or radius) Above fsresistance/loss increases

proportional to sqrt(frequency)

26

d

eJ

= ( ) 21

= f

2

2

=

hfs

( )2

1

=

s

DCffRfR

2

1

02

=

s

DCR

f

f

Z

R

For rectangular conductor:

[Dally]


27/43

Skin Effect (Resistive Loss)

27

[Dally]

MHzfmR sDC 43,7 ==

5-mil Stripguide

kHzfmR sDC 67,08.0 ==

30 AWG Pair

2

1

02

=

s

DC

R f

f

Z

R


28/43

Dielectric Absorption (Loss)

An alternating electric fieldcauses dielectric atoms torotate and absorb signalenergy in the form of heat

Dielectric loss is expressedin terms of the losstangent

Loss increases directlyproportional to frequency

28

CG

D

=tan

LCf

CLfCGZ

D

D

D

tan

2tan2

2

0

=

==

[Dally]


29/43

Total Wire Loss

29

[Dally]


30/43

Reflections & Telegraphers Eq.

30

T

iT

ZZ

VI

+=

0

2

+

=

+=

=

0

0

0

00

2

ZZ

ZZ

Z

VI

ZZ

V

Z

VI

III

T

Tir

T

iir

Tfr

0

0

ZZ

ZZ

V

V

I

Ik

T

T

i

r

i

rr

+

===

Termination Current: With a Thevenin-equivalent model of the line:

KCL at Termination:

Telegraphers Equation or

Reflection Coefficient

[Dally]


31/43

Termination Examples - Ideal

31

RS = 50

Z0= 50, td = 1ns

RT = 50

0

5050

5050

05050

5050

5.05050

501

=

+

=

=+

=

=

+

=

rS

rT

i

k

k

VVV

in (step begins at 1ns)

source

termination


32/43

Termination Examples - Open

32

RS = 50

Z0= 50, td = 1ns

RT ~ (1M)

0

5050

5050

150

50

5.05050

501

=

+

=

+=+

=

=

+

=

rS

rT

i

k

k

VVV


source

termination


33/43

Termination Examples - Short

33

RS = 50

Z0= 50, td = 1ns

RT = 0

0

5050

5050

1500

500

5.05050

501

=

+

=

=+

=

=

+

=

rS

rT

i

k

k

VVV


source

termination


34/43

Arbitrary Termination Example

34

RS = 400

Z0= 50, td = 1ns

RT = 600

778.0

50400

50400

846.050600

50600

111.050400

501

=

+

=

=+

=

=

+

=

rS

rT

i

k

k

VVV


sourcetermination

0.111V

0.205V

0.278V0.340


35/43

Lattice Diagram

35

RS = 400

RT = 600

Z0= 50, td = 1ns


Rings up to 0.6V(DC voltage division)


36/43

Termination Reflection Patterns

36

RS = 25, RT = 25

krS& krT< 0

Voltages Converge

RS = 25, RT = 100

krS < 0 & krT> 0

Voltages Oscillate

RS = 100, RT = 25

krS > 0 & krT< 0

Voltages Oscillate

RS = 100, RT = 100

krS > 0 & krT> 0

Voltages Ring Up

source

termination

source

termination

source

termination

source

termination


37/43

Termination Schemes

37

No Termination Little to absorb line energy

Can generate oscillatingwaveform

Line must be very short

relative to signal transition time n = 4 - 6

Limited off-chip use

Source Termination Source output takes 2 steps up Used in moderate speed point-

to-point connections

LCnlnTt triproundr 2=>

LCltporch 2


38/43

Termination Schemes

38

Receiver Termination No reflection from receiver

Watch out for intermediateimpedance discontinuities

Little to absorb reflections at driver

Double Termination

Best configuration for minreflections

Reflections absorbed at both driver

and receiver

Get half the swing relative tosingle termination

Most common termination schemefor high performance serial links


39/43

Differential Transmission Lines

39

Differential signaling advantages

Self-referenced

Common-mode noise rejection

Increased signal swing

Reduced self-induced power-supply noise

Requires 2x the number ofsignaling pins relative to single-ended signaling

But, smaller ratio ofsupply/signal (return) pins

Total pin overhead is typically1.3-1.8x (vs 2x)

[Hall]

Even mode

When equal voltages drive bothlines, only one mode propagatescalled even more

Odd mode

When equal in magnitude, but outof phase, voltages drive both lines,only one mode propagates calledodd mode


40/43

Balanced Transmission Lines

Even (common) modeexcitation

Effective C = CC

Effective L = L + M Odd (differential) mode

excitation

Effective C = CC + 2Cd Effective L = L M

40

21

21

2

+

=

+=

dc

odd

c

even

CC

MLZ

C

MLZ

[Dally]

2,2 evenCModdDIFF

ZZZZ ==


41/43

PI-Termination

41

1RZeven =

2||2|| 221 RZRRZ evenodd ==

=

oddeven

evenodd

ZZ

ZZR 22


42/43

T-Termination

42

12 2RRZeven +=

( )oddeven

odd

ZZR

RZ

=

=

21

1

2


43/43

Next Time

Channel modeling Time domain reflectometer (TDR)

Network analysis

lecture2 ee689 channels

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