lecture4 ee689 tline examples

8/10/2019 Lecture4 Ee689 Tline Examples

1/17

Sam Palermo

Analog & Mixed-Signal Center

Texas A&M University

ECEN689: Special Topics in High-Speed

Links Circuits and SystemsSpring 2010

Lecture 4: Transmission Line Examples


2/17

Announcements

HW1 due 1/29 One page summary of recent link design paper

Current Reading

Chapter 3.3 3.4

For next time

Chapter 3.6 3.7

2


3/17

Agenda

Transmission Lines Termination examples

Differential transmission lines

Majority of todays material from DallyChapter 3.3-3.4

3


4/17

Reflections & Telegraphers Eq.

4

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]


5/17

Termination Examples - Ideal

5

RS = 50Z0 = 50, td = 1ns

RT = 50

05050

5050

05050

5050

5.05050

501

=+

=

=+

=

=

+=

rS

rT

i

k

k

VVV

in (step begins at 1ns)

source

termination


6/17

Termination Examples - Open

6

RS = 50Z0 = 50, td = 1ns

RT ~ (1M)

05050

5050

150

50

5.05050

501

=+

=

+=+

=

=

+=

rS

rT

i

k

k

VVV


source

termination


7/17

Termination Examples - Short

7

RS = 50Z0 = 50, td = 1ns

RT = 0

05050

5050

1500

500

5.05050

501

=+

=

=+

=

=

+=

rS

rT

i

k

k

VVV


source

termination


8/17

Arbitrary Termination Example

8

RS = 400Z0 = 50, td = 1ns

RT = 600

778.050400

50400

846.050600

50600

111.050400

501

=+

=

=+

=

=

+=

rS

rT

i

k

k

VVV


sourcetermination

0.111V

0.205V

0.278V0.340


9/17

Lattice Diagram

9

RS = 400

RT = 600

Z0 = 50, td = 1ns


Rings up to 0.6V(DC voltage division)


10/17

Termination Reflection Patterns

10

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


11/17

Termination Schemes

11

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


12/17

Termination Schemes

12

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 driverand receiver

Get half the swing relative tosingle termination

Most common termination schemefor high performance serial links


13/17

Differential Transmission Lines

13

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 of supply/signal(return) pins

Total pin overhead is typically 1.3-1.8x (vs 2x)

[Hall]


14/17

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

14

21

21

2

+

=

+=

dc

odd

c

even

CC

MLZ

C

MLZ

[Dally]

2,2 oddCMevenDIFF

ZZZZ ==


15/17

PI-Termination

15

1RZeven =

2||2|| 221 RZRRZ evenodd ==

=

oddeven

evenodd

ZZ

ZZR 22


16/17

T-Termination

16

12 2RRZodd +=

( )oddeven

odd

ZZR

RZ

=

=

2

11

2


17/17

Next Time

Channel modeling Time domain reflectometer (TDR)

Network analysis

17

lecture4 ee689 tline examples

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