Clk&PllliCrosstalk & Parallelismisb.nu.edu.pk/rfcs2/documents/indcourses/Lec6_Parallesim_Xtalk_DiffrenPair.pdfClk&PllliCrosstalk & Parallelism Rashad.M.Ramzan, Ph.D FAST-NU, Islamabad

C lk & P ll liCrosstalk & Parallelism

Rashad.M.Ramzan, Ph.D

FAST-NU, Islamabad

Today's Topicsoday s op cs

• Crosstalk and Parallelism– Overview

Definition Sources and Dependence– Definition, Sources and Dependence

– Crosstalk Models for simulation

– Near End and Far End Crosstalk

– Crosstalk dependence on terminationp

– Impedance variation due to crosstalk

Case Study– Case Study

High Speed PCB Design: Lecture-6 © Rashad.M.Ramzan 2010-11 2

Noise: Cumulative OverviewNo se: Cu u at ve Ove v ew


Noise Coupling Via InterconnectNo se Coup g V a te co ect


CrosstalkC ossta• Mutual interference between two circuits give rise to the

crosstalkcrosstalk.

• Inductive Crosstalk (proportional to di/dt of the driven line).

• Capacitive Crosstalk (proportional to dv/dt of the driven line).

• Common Path Crosstalk - Resistive Crosstalk proportional to p pthe current flow.

• Inductive crosstalk > capacitive crosstalk in digital circuits.p g


CrosstalkC ossta

• Crosstalk occurs at– On-Chipp– On Chip Package– On PCB– On ConnectorsOn Connectors– On Connector Cables

• Crosstalk change and modify the Zo and propagation delay. This effects system level timing hence Signal Integritysystem level timing hence Signal Integrity.

• Crosstalk depends upon data pattern, line to line spacing and switching rates.


Crosstalk Circuit Model

On ChipOn-Chip

dI

Off-Chip dt

dILV driver

mLnoise m=,

dt

dVCI driver

dCnoise m=,


Inside IC: Cap Dominatess de C: Cap o ates


Crosstalk: Mutual Capacitance & Inductancep


Near end and Far end CrosstalkNea e d a d a e d C ossta

N d t lk ill b i t•Near end cross talk will begin at time t=0 and will have duration t=2Td•Far end cross talk will begin at time t=Td and will have duration equal signal rise or fall time.g•The amount and shape depends upon the coupling and termination


Near-end and far-end crosstalkNea e d a d a e d c ossta


Inductive Coupling (Forward & Reverse)p g ( )

• The negative blip size at the far end is proportional to the total mutual inductance.

• Lengthening the line increases the size of blip at D.

• Height of the positive reverse coupling peak length of line.


Capacitive Coupling (Forward & Reverse)p p g ( )

Th t f d ff t l t D• The two forward effects cancel at D.

• Striplines are well balanced between inductive and capacitive couplingcoupling.

• Microstrip electric field lines travel through air (cap coupling smaller)yielding small negative forward coupling coefficient.


)y g g p g

Total Crosstalkota C osstaCombining Mutual Inductive and Capacitive Coupling:

TCL1 ⎫⎧

• Amplitude of the crosstalk waves may be approximated by

VT

T

C

C

L

L

2

1V d

r

PMMf

⎭⎬⎫

⎩⎨⎧ −=

)2TT(forVC

C

L

L

4

1V Prd

MMb <

⎭⎬⎫

⎩⎨⎧ +=

CL4 ⎭⎩

F d t lk ld b d b li• Forward crosstalk could be made zero by a proper line arrangement


Total Crosstalkota C osstaHow Near-End Crosstalk becomes a Far-End Problem

Reverse coupling reflecting from a low impedance d idriver

Termination to Reduce Crosstalk

A

B

C

Reverse coupling

appearing at Cif termination is Zo

T

DSignal at D due toreverse couplinggetting reflected at D

Tp

Tp Tp Tp0 2 3


Tp Tp Tp0 2 3

Near, Far end Crosstalk & Termination,


Odd and Even Mode FieldsOdd a d ve ode e ds


Impedance variation and Crosstalkpeda ce va at o a d C ossta


Crosstalk: Switching Pattern Dependenceg p


Crosstalk: Switching Pattern Dependenceg p

1211

1211

LLL

CCC

even

even

+=−=

1211

1211

LLL

CCC

odd

odd

−=+=

1211 LLLZ even +

==

1211

1211

CC

LL

C

LZ

CCCZ

oddodd

eveneven

−==

−


1211 CCCoddodd +

Noise-on-Delay Effect: CrosstalkNo se o e ay ect: C ossta


Examplea p eCross-talk=R2CM/T10-90, =4pF*37 5Ω/5ns=0 03(3%)4pF 37.5Ω/5ns 0.03(3%) still OK.But when T10-90 = 1 ns, cross-talk=15% !!


Examplea p e• Cross-talk=CMR(input R of

/receiver) /Tr

• It is still OK, if the input h ll l ll R fhas a parallel small R of 75Ω. Cross-talk=3%.

• If R2 = 10K (ie Open• If R2 = 10K (ie Open Collector), crosstalk=800%.

• Rule: Add capacitors connected to large pull-up resistors for reducing cross-talk.


Crosstalk vs. Geometry of TracesC ossta vs. Geo et y o aces


Crosstalk vs. Geometry of TracesC ossta vs. Geo et y o aces


Crosstalk in Solid GND PlaneC ossta So d GN a e


Crosstalk in Slotted GND PlaneC ossta S otted GN a e


Crosstalk in Slotted GND PlaneC ossta S otted GN a e


Crosstalk in Crosshatched GND PlaneC ossta C oss atc ed GN a e


Crosstalk with PWR and GND FingersC ossta w t W a d GN ge s


Guard Rings: Reduce the CrosstalkGua d gs: educe t e C ossta


How much Crosstalk?ow uc C ossta ?

How much crosstalk is too much?

• Crosstalk level of 1-3% between adjacent wires is fine

• Assumes that there exists solid ground plane• Assumes that there exists solid ground plane

• Each wire interacts only with its nearest neighbours

• Cross-coupling from other more remote wires is negligible


Rule to Minimize Crosstalku e to e C ossta


Case Study: False TriggeringCase Study: a se gge g

Problem:8 Bit wide Bus, Four Layer boardDriving Buffer Rs = 30 ΩSwing = 2V, Length of trace= 5 in

Goals is to Determine:1. Self inductance and Capacitance.g , g

Center-Center Spacing =15 Mil, Zo(with Out Cross talk) = 50 Ωε = 4.0 (FR4)

2. Max impedance variation due to Crosstalk?

3. Max velocity variation due to Crosstalk?εr 4.0 (FR4)

Input Buffer capacitance << ignoredMutual inductance = 0.54 nH/inMutual Capacitance = 0 079 pF/in

Crosstalk?4. Input buffer at U2 will switch at 1.0V,

if there is possibility of false triggering?


Mutual Capacitance = 0.079 pF/in triggering?

Case Study: False TriggeringCase Study: a se gge g1. Self Inductance and Capacitance:

1−

FHWFR

WH

TF

W

Hr

rre

023/5/4)4(

)1(217.012

12

1

2

1 2

1

=⇒==

−−+⎥⎦⎤

⎢⎣⎡ +

−+

+=

−

ε

εεεε

FHWFR

e

r

)23(05

0.1)14(217.00

5

)2.3(121

2

14

2

14

02.3/5/,4)4(

2

1

−−+⎥⎦⎤

⎢⎣⎡ +

−+

+=

=⇒==−

ε

ε

smsmc

v

e

/10781/100.3

84.2

)2.3(0.5522

88

×=×

==

=⎦⎣

εpsin

ps

inpsinVelocity

713

/0070.0713

5)/( ==

psi

minlengthTD

smv

r

r

713)01

0254.0(

/10781

0.5

/1078.184.2

8===

×===

ε

ε

C

LZ

inpsin

psLCinchperTD

o 50

/6.1420.5

713)(

Ω==

===

Qpinsmc

)0.1

(/1078.1 8×

pFps

CL

LC

Z

TDC

C

o

85.250

6.142====⇒


nHCLLCZTDL o 13.7=×=×=⇒

Case Study: False TriggeringCase Study: a se gge g2. Max Velocity variation due to Crosstalk



CCC

LLLZ common

231222

231222,2 −−

++=

pFpFpF

nHnHnHZ common 26.55

079.0079.085.2

54.054.013.7,2 Ω=

−−++

=

CCCLLLTD common ))(( 231222231222,2 −−++=

inpsTD

pFpFpFnHnHnHTD

common

common

/6.148

)079.0079.085.2)(54.054.013.7(

,2

,2

=

−−++=





CCC

LLLZ ldiffrentia

231222,2 ++

−−=

pFpFpF

nHnHnHZ

CCC

ldiffrentia 8.4407900790852

54.054.013.7,2

231222

Ω=++−−

=

++

CCCLLLTD

pFpFpF

ldiffrentia ))((

079.0079.085.2

2312222312222 ++−−=

++

inpsTD

pFpFpFnHnHnHTD

ldiff ti

ldiffrentia

ldiffrentia

/135

)079.0079.085.2)(54.054.013.7(

))((

2

,2

231222231222,2

=

++−−=

inpsTD ldiffrentia /135,2

impadanceandvelocityinVariation

psTDps

Z

impadanceandvelocityinVariation

o

6148135

26.558.44

<<Ω<<Ω


psTDps 6.148135 <<

Case Study: False TriggeringCase Study: a se gge g3. If Crosstalk will induce false triggering?

The signal will ring down to a minimum voltage gof 1.84V.

Since the threshold voltage of thisvoltage of this buffer was defined to be 1.0V, and signal does not ring back down toring back down to this value.

The signal i t it ill tintegrity will not cause false triggering.


SummerySu e y• There in no velocity variation due to Crosstalk in Striplines but

there is in Microstripthere is in Microstrip.

• The nearest neighbor has greatest effect.

• Common mode (All bit in phase) and differential (only target• Common mode (All bit in phase) and differential (only target out of phase) mode produce worst velocity and impedance variation.

• Low impedance line produces less impedance variation.

• The impedance of the trace is effected by the proximity of the p y p yneighbor traces even when they are not driven,

• Mutual parasitic falls off exponentially with trace-to-trace spacing.


Wakeup Please lets havepSome Food….

42

Documents

Clk&PllliCrosstalk & Parallelismisb.nu.edu.pk/rfcs2/documents/indcourses/Lec6_Parallesim_Xtalk_DiffrenPair.pdfClk&PllliCrosstalk & Parallelism Rashad.M.Ramzan, Ph.D FAST-NU, Islamabad