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VARIABLE SWING Optimal Parallel LINKs Minimal Power, Maximal density for parallel links configurations Claudia P. Barrera advisor: fouad kiamilev PhD committee: Allen Barnett guang gao mayra sarmiento. Ph.D. Dissertation Defense. Outline. Outline - Introduction. Motivation. Motivation.

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Ph d dissertation defense

VARIABLE SWING Optimal Parallel LINKsMinimal Power, Maximal density for parallel links configurationsClaudia P.Barreraadvisor: fouad kiamilevPhD committee: Allen Barnett guang gao mayra sarmiento

Ph.D. Dissertation Defense



Outline introduction
Outline - Introduction



Motivation1
Motivation

  • Mobility

  • Mobile devices require low power, high data rates

    • Increasing multimedia applications

    • Higher definition displays

    • Smaller sizes

    • Battery life


Motivation2
Motivation

  • Size

  • Transistor size still decreasing

  • Moore’s Law still valid

  • Higher computational capabilities on-chip but interconnect requirements constrain the size of the devices


Motivation3
Motivation

Source: Intel Corporation - http://www.intel.com/technology/timeline.pdf


Motivation4
Motivation

  • Speed

  • Required higher data rates

    • Multimedia applications

    • High Performance Computing

    • Off-chip speed is the bottleneck for high speed communications

2003 ITRS (International Technology Roadmap for Semiconductors) roadmap for on-chip and off-chip speed.

Taken from http://www.ieee.org/organizations/pubs/newsletters/leos/oct04/summer.html


Problem statement
Problem Statement

POWER SAVINGS

  • Design Stage

    • Need of communication between A and B

      • Length

      • Speed

      • Power

MAXIMUM LINE LENGTH / SPEED

8 – 16mA - TX current

3.5mA - TX current

0.1mA - TX current

CML

LVDS

WhisperBus

Standard

Fixed TX Power

A

B

Communication

If length is long, a high TX

power is OK

But if the distance between

A and B is short, there will be a

Waste of Power.


Problem statement1
Problem Statement

  • Design Stage

    • Maximum data rate allowed in the communication

      • Serial

      • Parallel

Data Rate: X

Data Rate: 4X

P

P

SERDES

Serializer - Deserializer

B

A

SERDES

SERDES

P

P


Problem statement2
Problem Statement

  • Design Stage

    • Maximum data rate allowed in the communication

      • Serial

      • Parallel

Data Rate: X

Data Rate: 4X

P

P

SERDES

Bandwidth Increment

4X

4X

P

P

A

B

P

P

P

P

4X

4X

Then, what is the problem with parallel links?


Problem statement3
Problem Statement

  • Space…

1

2

A

B


Problem statement4
Problem Statement

  • Space…

A

B


Problem statement5
Problem Statement

  • Space…

A

B

A

Bandwidth Limitation by maximum number of wires that can be routed


Previous work
Previous Work

  • Optimization based on free parameters

    • Geometry

w

d

t

h

εr


Previous work1
Previous Work

  • 3D approach to eliminate crosstalk

  • Not feasible for a PCB


Previous work2
Previous Work

  • Jitter equalization technique that induces a data dependent delay to compensate for crosstalk jitter

  • Quantification of crosstalk-induced jitter from the mutual capacitance and inductance between two adjacent lines


Serial power optimization technique vsmpl
Serial Power Optimization TechniqueVSMPL

POWER OPTIMIZATION ALGORITHM

BASED ON AN ACCELERATED BIT

ERROR RATIO (BER) MEASUREMENT

  • Set transmitter power to where BER~10-4

  • Increment power setting

  • Measure current BER

  • Repeat steps 2 and 3 several times

  • Fit a line through the data points

  • Estimate the transmitter power setting required to achieve the target BER

    J. Kramer


Serial power optimization technique vsmpl1
Serial Power Optimization TechniqueVSMPL

BER 2

BER 1

Accelerated BER Tester

Power setting 1

Power setting 2

Power set to 3

Power 3 =F(BER1,BER2)


Vsmpl in a bus configuration
VSMPL in a bus configuration

Accelerated BER Tester

1

2

BER increases

1

2

1

2

BER increases


Contribution of this work
Contribution of this work

  • Based on accelerated BER measurement:

    • Simple technique that reduces crosstalk

      • Novel technique using anti-coupling capacitors

      • Up to 87% reduction

    • Reflections are minimized

      • Termination resistor is adjusted dynamically

  • Once crosstalk and reflections are minimized:

    • Channels can be treated as serial links.

    • Serial power optimization technique can be applied

MINIMAL POWER, MAXIMUM DENSITY FOR A PARALLEL LINK


Outline crosstalk
Outline - Crosstalk


Transmission line modeling
Transmission line modeling

w

t

εr

h

Microstrip

Stripline

Wire Pair




Coupling between transmission lines1
Coupling between transmission lines

Aggressor

Victim

Near End

Far End

Near End

Far End


Coupling between transmission lines2
Coupling between transmission lines

Vb

Time

RT

Far End noise

Near End noise

RT: Rising Time

TD: Time Delay

Vb

Near End

Far End

TD

Time

RT

2 x TD


Coupling between transmission lines3
Coupling between transmission lines

C14

C24

C13

C12

C23

C34

1

2

3

4

C11

C22

C33

C44


Differential signaling
Differential Signaling

V1

1

+

Vo=V1-V2

2

-

V2

Advantages:

Tolerance to ground offsets

Low voltage

High immunity to common noise


Crosstalk in differential signaling
Crosstalk in differential signaling

The problem of crosstalk in differential signaling is that generates a non common noise.

The effect of electromagnetic fields is higher on the closest line

V1-V2

(V1+b*Vn)-(V2+d*Vn)

d* > b*

V1

V2

Vn

V1

V2

Vn

Differential pair with a quiet line routed closely

Noise effect in a differential pair when an active line is routed closely


Crosstalk in differential signaling1
Crosstalk in differential signaling

C14

Aggressor

Victim

C24

+

-

+

-

C13

C23

Transmission lines are linear systems

Superposition can be applied

VV+

VV-

VA+

VA-

Victim

Aggressor

VA+=-VA-

VV+=VA+*(C13)+VA-*(C14)

VV-=VA+*(C23)+VA-*(C24)

VV=VV+-VV-


Anti coupling capacitances
Anti-Coupling Capacitances

C14

C24

Using superposition principle…

C13

VV+=VA+*(C13)+VA-*(C14)

C23

+VA-*(Anti-C13)+VA+*(Anti-C14)

+

-

+

-

VV-=VA+*(C23)+VA-*(C24)

VA+=-VA-

VV=VV+-VV-

Anti-C24

+VA-*(Anti-C23)+VA-*(Anti-C24)

Anti-C14

Anti-C23

Anti-C13


Reflections
Reflections

  • Reflections happen when the transmission line is not matched.

Output impedance

Characteristic Impedance Zo

Termination

Impedance


Optimization algorithm
Optimization algorithm

BERT

+

  • Tune the termination resistor on the receiver based on the BER measurement on the link at low power.

  • Tune the anti-coupling capacitances:

    • Turn on the victim line at low power (so that BER is in the order of 10-4)

    • Turn on one neighbor at the highest power. The BER in the victim line will increase due to crosstalk noise.

    • Tune anti-coupling capacitance until minimum BER is reached.

  • Review impedance matching for the line. Repeat 1 and 2 until stable.

  • Apply serial power optimization to each line.

Anti-C23

-

Anti-Cb

Anti-C23

+

-


Outline testing simulation platforms and results
Outline – Testing, Simulation Platforms and Results


Testing platform
Testing Platform

BERT

Labview Card

Anritsu Digital Data Analyzer

RX

TX

PRBS

Generator



Testing results1
Testing Results

35uA

48uA

63uA


Simulation platform
Simulation Platform

W-Element Matrix


Experiments setup
Experiments setup

6.5mils

4mils

Aggressor

4mils

Victim

5.7 mils

100mm





Effect of anti coupling capacitors
Effect of anti-coupling capacitors

  • Differential pairs routed as close as manufacturing technology allows

    • One aggressor

    • One victim

  • Measured the differential voltage on the victim and report the highest noise (voltage)

  • Placed 4 capacitors and started to change the value of one of them until the minimum crosstalk was reached.


Effect of anti coupling capacitance
Effect of anti-coupling capacitance

  • By adding the anti-coupling capacitance, the crosstalk is reduced up to 78%.


Required spacing to achieve same performance
Required spacing to achieve same performance

  • Increase spacing between the 2 lines by 1X and measure the highest noise.

  • Repeat previous step until performance of anti-coupling capacitors is reached


Required spacing to achieve same performance1
Required spacing to achieve same performance

  • To achieve the same crosstalk reduction, the spacing between differential lines must be 6X

Anti-coupling capacitances performance


Fft of the signal induced by crosstalk in the quiet line
FFT of the signal induced by crosstalk In the quiet line

  • -Minimum spacing between differential

  • channels

  • -- 5X spacing between differential

  • channels

  • -- Minimum spacing between differential

  • Channels using anti-coupling cap

Power noise on the victim line is reduced significantly when an anti-coupling capacitance is used. The effect of adding the anti-coupling capacitors is actually better than spacing the channels by the rule of thumbs given by the literature.


Far end noise time domain
Far end noise – time domain

Aggressor

-- No anti-coupling capacitances

-- Effect of anti-coupling capacitances in time domain

Victim


Effect of anti coupling capacitances in induced jitter
Effect of anti-coupling capacitances in induced jitter

-- No anti-coupling capacitances

-- Effect of anti-coupling capacitances

140ps

17ps


Optimization of anti coupling capacitances
Optimization of anti-coupling capacitances

Anti-C13 = Anti-C24 = 0.8pF

Anti-C14 and Anti-C23

Variable


Optimization of anti coupling capacitances1
Optimization of anti-coupling capacitances

Minimum crosstalk noise power : 0.7mW

Without the anti-coupling capacitances: 3.3mW

79% less noise power


Optimization of anti coupling capacitances2
Optimization of anti-coupling capacitances

Symmetrical response, and minimum crosstalk noise in both channels:

Anti-C13 = Anti-C24

Variable

Anti-C14 = Anti-C23

Variable


Optimization of anti coupling capacitances3
Optimization of anti-coupling capacitances

Minimum crosstalk noise power : 0.4mW

Without the anti-coupling capacitances: 3.3mW

87% less noise power


Impact of anti coupling capacitances
Impact of anti-coupling capacitances

The use of anti-coupling capacitances allow routing of high speed paths as close as possible without performance impact.

Each channel is transmitting at 10Gbps using the minimum space allowed by the manufacturer.


Outline conclusions
Outline - Conclusions


Conclusions
Conclusions

  • Optimize the signal integrity and power of a differential parallel link

  • Higher bandwidth-per-unit-area

  • Anti-coupling capacitors cancel out the effect of mutual impedances in the transmission lines.

  • Implementation increases six times the bandwidth-per-unit-area in a parallel link communication

  • Accelerated BER measurement gives a new perspective to electrical interconnect designers since it opens new possibilities of dynamically improving performance of the link according to its specific needs.


Future work
Future Work

  • Implementation on FPGA:

    • capability of adjusting the power of the transceivers, or selecting a proper termination resistor is given, e.g. Rocket IO.

    • BERT is a given component, easy implementation in VHDL.

    • Addition of the anti-coupling capacitances off-chip.


Future work1
Future Work

  • Improvement of the optimization methodology

    • Faster convergence by optimization techniques

    • More capacitances for longer paths can be studied

    • Effect of capacitances on the transmission line’s bandwidth

  • The work can be extended for:

    • Single ended configurations

    • On-chip communication


Publications
Publications

  • C.P. Barrera, F. Kiamilev, J. Kramer, J. T. Ekman, - Testing of the Next Generation variable-swing Multi-gigabit Chip-to-Chip Interconnect for Bus Configurations, The 18th Annual IEEE Workshop on Interconnections within High Speed Digital Systems, May 2007, Santa Fe, NM

  • C.P. Barrera, J. Helou, J. Kramer, J. Ekman, N. Waite, Prof. F. Kiamilev, “Trusted Foundry ASIC designs - University of Delaware” presented at the DARPA and OSD Trusted Foundry Circuit Designers Meeting, September 12-13, 2007 in Burlington, VT.

  • J. Kramer, C.P. Barrera, F. Kiamilev - Accelerated Bit Error Rate Measurement Technique for Multi-link Gigabit interconnects, In preparation for TCAS - IEEE Transactions on Circuits and Systems I

  • C.P. Barrera, F. Kiamilev, N. Waite, - Variable Swing Optimal Parallel links – Minimal power, Maximal density for parallel links, Accepted for The 20th Annual IEEE Workshop on Interconnections within High Speed Digital Systems, May 2009, Santa Fe, NM

  • C.P. Barrera, F. Kiamilev, N. Waite – Crosstalk Cancellation Using Anti-Coupling Capacitances, In preparation for JQE – IEEE Journal in Quantum Electronics


Acknowledgments
Acknowledgments

  • Dr. Kiamilev

  • Committee Members:

    • Dr. Barnett

    • Dr. Gao

    • Dr. Sarmiento

  • Dr. Kramer, Jirar Helou, Nick Waite

  • Andres

  • CVORG

  • Friends

  • Family in Colombia

  • God


Questions
Questions?

Thank you


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