ece 145a / 218 c, notes set 2: transmission line parasitics

class notes, M. Rodwell, copyrighted 2009-14

ECE 145A / 218 C, notes set 2: Transmission Line Parasitics

Mark Rodwell

University of California, Santa Barbara

[email protected] 805-893-3244, 805-893-3262 fax


Transmission Lines

Approximate properties of microstrip line.

Skin Effect Losses

substrate modes and loss by coupling into these.

Lateral modes on lines

Excitation of unwanted circuit-like modes, ground continuity

Packaging and power supply resonances


Skin Loss


Skin effect losses I

jk

j

jjkkkk

jjkkkk

x

y

yzy

zy

2

2222

2222

so , sfrequencie lowat metal, aIn

))(( so

small, is metal theintocurrent of distancen penetratio theand

long, is line-ion transmiss thealongh wavelengtThe

))(( where

) variation (ignore metal insideequation Wave

zy

x


Skin effect losses II

nm 200 Gold,in 100GHzAt

as varies

depth skin theisdepth n penetratio )(1/ The

metal. theinto distancelly with exponentiadown dies field The

)(

:/2 as *depthskin * theDefining

21

so , sfrequencie lowat metal, aIn

2/1

//

e

eeEzE

jjk

j

jyy

o

y

zy

x


Skin effect losses III

appendix. theSee

impedance. surface ofconcept thedevelops treatmentcareful moreA

2/)/1(2/)/1(/1/

length unit per resistance hasconductor the

, width and ty conductiviWith

. thicknessoflayer ain current carriesonly conductor The

:elyapproximat s treat thiusLet

WWWLR

W

series

zy

x


Skin effect losses IV

periphery. carrying-current effective theis where

2/)/1(/1/

as thiscan write wegeneral,In

11

2

11

2

1111/

:microstripFor .conductors ground and signal the

both in effect skin have lines-onTransmissi

P

PPLR

PHWWHWWLR

series

series

H

W

~W +2H


Skin effect losses IV

lossskin called is This

2

/

distanceunit per n attenuatio introduces this

analysis, line-ansmissionearlier trour From

2/)/1(/

0

Z

LR

PLR

series

series


Loss Tangent


Loss Tangent

class. in thisfurther thesediscussnot willbut we

losses, dielectric of aware be should We

))tan(1(

* tangentloss* aby quantified iseffect This

n.attenuatiofrequency -high introduce also sdielectricCommon

realr,imaginaryr,realr,r jj


transverse

transmission-line

modes


Lateral Modes (1)

2222

2222222

0

/

,...2 ,1 ,0for / and 0

:line-ssionon transmi *laterally* propagatecan Waves

2

form of waves:dielectricIn

Wnck

nWnkk

ckkkk

eeeeE

rz

xy

drzyx

zjkyjkxjktj zyx


Lateral Modes (2)

222

222

2222

/

: /2 if n propagatio Evanescent 2)

/

/2. ifn propagatio mode-Multi )1

/

cWn

We

Wnc

W

Wnck

rz

d

z

rz

d

rz

z


Lateral Modes---and Junction Parasitics (3)

parasiticsjunction modelmust

.wavelength-half ahan narrower tmuch bemust lines

:Lessons

.simulation neticelectromagor models,junction library ADS

parasiticsjunction modes evanescentin power Reactive

: /2 if n propagatio Evanescent

d

zWe z


Substrate Modes

and

Radiation Loss


Substrate Modes

,...2 ,1 ,0for /

: thicknesssubstrate theacross wavesstanding havecan We

2

form of waves:dielectricIn

2222222

0

nhnk

ckkkk

eeeeE

y

drzyx

zjkyjkxjktj zyx

zy

x


Substrate Modes

.sfrequencielow at confined weakly ; 4 as confinedstrongly

mode;- tranversemetal topno withSubstrate

...23 , ,2 withmodes

surfaces metal bottom top, withSubstrate

T

E

h

d

ddd


Substrate Mode Coupling: Microstrip

4 when coupling mode strongVery

s.frequencie allat loss )radiation"(" coupling mode Nonzero

.in and in propagecan modes slab dielectric These

dh

zx


Substrate Mode Coupling: CPW

and 2 where

form of are Waves

) thickness(substrate2 when allowed are modes Substrate

22222222

0

d

hnkckkkkk

eeeeE

ydrzyx

zjkyjkxjktj zyx

zy

x


Substrate Mode Coupling: CPW

kz

loss" radiation"

frequencydimensions e transversline dB/mmloss, coupling mode

: substrate, thick Given

henstrongly w couple Modes

22

mode substrate,CPW,

d

yy

H

kk


Transmission-Line Losses

problems.major be will

radiation substrate and modes lateral then

substrates thick and lines wideuse weIf

large. be willlosseseffect -skin then

substrates thin and lines narrow use weIf


Loss of Coaxial Cable

0.01

0.1

1

10

1 10 100 1000

Atte

nu

atio

n, d

B/m

ete

r

Frequency, GHz

10 mm cable:0.7 dB/m at10 GHz cutof f

3 mm cable:3.1 dB/m at33 GHz cutof f

1 mm cable:14 dB/m at 100 GHz cutof f

1.2r4103)tan(

12/1)/2( requiresn propagatio mode-Single outerinnerr DDcf

2/32/1 Loss / lossSkin fDf skininnerskin


"circuit-type"

parasitic modes


Transmission-Line Parasitic Modes


To Avoid "Circuit-Type" Parasitic Modes


Example of Parasitic Mode Excitation

I/2

I

I/2

I/2

I

I/2

I/2I/2

A slot-line mode is excited

at a CPW junction

I/2

I

I/2

I/2

I

I/2

The fix...

this is one of many possible

examples...


Example of IC using CPW wiring

1-180 GHz HEMT amplifier (UCSB / HRL)

Note the ground bridges

B. Agarwal UCSB, M. Matloubian, HRL


package resonance

and grounding


What is Ground Bounce ?

ADC digital sections

input buffer

ground return currents

L ground

D V in ground

bounce

noise

"Ground" simply means a reference potential shared between many circuit paths.

To the extent that it has nonzero impedance, circuits will couple in unexpected ways

RFI, resonance, oscillation, frequently result from poor ground systems


Ground Bounce on an IC: break in a ground plane

signal line

signal line

ground

plane

line 1

“ground”

line 2

“ground”

common-lead inductance

coupling / EMI due to poor ground system integrity is common in high-frequency systems

whether on PC boards

...or on ICs.


Ground Bounce: IC Packaging with Top-Surface-Only Ground

Bond wire inductance aggravates the

effect: resonates with through-wafer

capacitance at 5-20 GHz

Peripheral grounding allows parallel plate mode resonance

die dimensions must be <0.4mm at 100GHz

IC: parallel-plane transmission line

peripheralbond inductances

peripheralbond inductances


Substrate Microstrip: Eliminates Ground Return Problems

a

Brass carrier andassembly ground

interconnectsubstrate

IC with backsideground plane & vias

near-zeroground-groundinductance

IC viaseliminateon-wafergroundloops


power-supply resonance


Power Supply Resonance

onbondCLf 2/1


Power Supply Resonances; Power Supply Damping

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100

po

we

r su

pp

ly im

pe

da

nce

, O

hm

s

Frequency (GHz)

90 GHz--local resonance between power supply capacitance and supply lead inductance

~N*5GHz resonances--global standing wave on power supply bus

Power supply is certain to resonate: we must model, simulate, and add damping during design.


Standard cell showing power busses


Interconnects:

Summary,

Design Strategy


kz

Parasitic slot mode

-V 0V +V

0

V

Coplanar Waveguide: Summary No ground vias

No need (???) to

thin substrate

Parasitic microstrip mode

+V +V +V

0

V

Hard to ground IC

to package

substrate mode coupling

or substrate losses

ground plane breaks → loss of ground integrity

Repairing ground plane with ground straps is effective only in simple ICs

In more complex CPW ICs, ground plane rapidly vanishes

→ common-lead inductance → strong circuit-circuit coupling

40 Gb/s differential TWA modulator driver

note CPW lines, fragmented ground plane

35 GHz master-slave latch in CPW

note fragmented ground plane

175 GHz tuned amplifier in CPW

note fragmented ground plane

poor ground integrity

loss of impedance control

ground bounce

coupling, EMI, oscillation

III-V:

semi-insulating

substrate→ substrate

mode coupling

Silicon

conducting substrate

→ substrate

conductivity losses


kz

Classic Substrate Microstrip: Summary

Strong coupling when substrate approaches ~d / 4 thickness

H

W

Thick Substrate

→ low skin loss

Hr

skin 2/1

1

Zero ground

inductance

in package

a

Brass carrier andassembly ground

interconnectsubstrate

IC with backsideground plane & vias

near-zeroground-groundinductance

IC viaseliminateon-wafergroundloops

High via

inductance

12 pH for 100 m substrate -- 7.5 W @ 100 GHz

TM substrate

mode coupling

Line spacings must be ~3*(substrate thickness)

lines must be

widely spaced

ground vias must be

widely spaced

all factors require very thin substrates for >100 GHz ICs

→ lapping to ~50 m substrate thickness typical for 100+ GHz

No ground plane

breaks in IC


fewer breaks in ground plane than CPW

III-V MIMIC Interconnects -- Thin-Film Microstrip

narrow line spacing → IC density

... but ground breaks at device placements

still have problem with package grounding

thin dielectrics → narrow lines

→ high line losses

→ low current capability

→ no high-Zo lines

H

W

HW

HZ

r

oo 2/1

~

...need to flip-chip bond

no substrate radiation, no substrate losses

InP mm-wave PA

(Rockwell)


No breaks in ground plane

III-V MIMIC Interconnects -- Inverted Thin-Film Microstrip


... no ground breaks at device placements







Some substrate radiation / substrate losses

InP 150 GHz master-slave latch

InP 8 GHz clock rate delta-sigma ADC


VLSI Interconnects with Ground Integrity & Controlled Zo

negligible breaks in ground plane


negligible ground breaks @ device placements







no substrate radiation, no substrate losses


No clean ground return ? → interconnects can't be modeled !

35 GHz static divider

interconnects have no clear local ground return

interconnect inductance is non-local

interconnect inductance has no compact model

InP 8 GHz clock rate delta-sigma ADC

8 GHz clock-rate delta-sigma ADC

thin-film microstrip wiring

every interconnect can be modeled as microstrip

some interconnects are terminated in their Zo

some interconnects are not terminated

...but ALL are precisely modeled


End


Appendix

(optional)


Skin effect losses I

E H

metal. theinto distance lly withexponentia down dies field ...the

)(

thatfind we/2 as depth skin theDefining

2/2/ then, If

)( where)( Hence

)( and

:metal ofsheet a onto direction in

incidentlarly perpendicu waveplanea Given

//

jzz

o

z

o

eeEzE

jj

jjeEzE

Ejz

HHj

z

E

z

IMPEDANCE. SURFACE theis This

termsinductive and resistive thenote11

hence,

22

:is metal thein impedance Wave

j

jj

j

j

H

E

metal

metal


Skin effect losses II

)1(

2

11

lines ground and

signal thein both impedance surface is thereline, microstrip For this

periphery. carrying-current effective theis P where,)1(1

of distanceunit per impedance series added an has thenline-ion transmissThe

depth skin thenlarger tha much is h wavelengtline-ion transmissthe

thatprovided seen, is impedance surface same but the surface, metal the

lar toperpendicunot parallel, travels wave theline, siona transmis In

j

HWWZ

j

PZ

series

series

H

W

~W +2H


Skin effect losses III

PZ

j

PZLCjZZLCj

LCZLCjLjZLCj

LjZLCjCjZLj

eVzV

Cj

PjPLj

Cj

ZLj

zI

zVZ

CVjz

IIZLj

z

Vj

PZ

oseries

seriesseries

seriesseries

z

o

serieso

seriesseries

line

00

line

line

22

12/

2// )2/1(

/1)(

where,)(

impedance sticcharacteri in changesecondary some....

//1

)(

)(

and )( )1(1

dispersion and loss both introduces thenThis

L

C/2

Zseries

L

C/2

Zseries

L

C/2

Zseries

L

C/2

Zseries

Skin Loss dispersion


Skin Effect losses, IV


Skin effect losses V

ece 145a / 218 c, notes set 2: transmission line parasitics

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