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Design Considerations in CLBs for Deep Sub-Micron Technologies. Louis Alarc ó n Octavian Florescu. Motivation. As technology scales… The effects due to process variations will become more pronounced. Regular structures are needed to mitigate these effects.

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Design Considerations in CLBs for Deep Sub-Micron Technologies

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Design considerations in clbs for deep sub micron technologies

Design Considerations in CLBs for Deep Sub-Micron Technologies

Louis Alarcón

Octavian Florescu


Motivation

Motivation

As technology scales…

  • The effects due to process variations will become more pronounced.

    • Regular structures are needed to mitigate these effects.

  • Leakage will increase as the VTH are scaled.

    • Low leakage architectures will be needed to control stand-by power.


Configurable logic block

Stack

Regular

Low Leakage

Slow due to RC delay

Current Sensing

Recover performance loss through smaller voltage swings.

Current

Sense

OUT

OUT

CLK

S

S

Pass

Transistor

Stack

Data

Inputs

Program

Bits

Configurable Logic Block


The stack

P0

B

S

A

to

sense

amp

Root

Input

B

Logic

Programming

(P0, P1, P2, P3)

S

A

B

B

The Stack

  • Inverted multiplexer tree

  • “pseudo-differential” currents at the outputs

  • Data inputs: 4

  • Program bits: 16


Sense amplifier topologies

I1

V2

V1

IOFF  0

V1

V2

ION

IBIAS

V = V1 - V2 > 0

ION

IOFF

CLB

V2

V1

ION

IOFF

Sense Amplifier Topologies

Conditional

Precharge

Sense

Amplifier

(CP)

Clamped

Bit-Line

Sense

Amplifier

(CBL)

DCVSL-based

Sense Amplifier

(DCVSL-SA)


Sense amplifier topologies1

I1

V2

V1

IOFF  0

V1

V2

ION

IBIAS

V = V1 - V2 > 0

ION

IOFF

V2

V1

CLB

ION

IOFF

Sense Amplifier Topologies

Conditional

Precharge

Sense

Amplifier

(CP)

Clamped

Bit-Line

Sense

Amplifier

(CBL)

DCVSL-based

Sense Amplifier

(DCVSL-SA)


Sense amplifier topologies2

I1

V2

V1

IOFF  0

ION

IBIAS

V1

V2

V = V1 - V2 > 0

ION

IOFF

V2

V1

CLB

ION

IOFF

Sense Amplifier Topologies

Conditional

Precharge

Sense

Amplifier

(CP)

Clamped

Bit-Line

Sense

Amplifier

(CBL)

DCVSL-based

Sense Amplifier

(DCVSL-SA)


Sense amplifier topologies3

I1

V2

V1

IOFF  0

ION

IBIAS

V = V1 - V2 > 0

V2

V1

ION

IOFF

Sense Amplifier Topologies

Conditional

Precharge

Sense

Amplifier

(CP)

V1

V2

ION

IOFF

CLB

Clamped

Bit-Line

Sense

Amplifier

(CBL)

DCVSL-based

Sense Amplifier

(DCVSL-SA)


Edp and leakage

Leakage Current

CBL

CMOS

CMOS

CP

CBL

TG

DCVSL-SA

DCVSL-SA

TG

CP

EDP and Leakage

EDP

Looks too good to be true? It probably is…


Process variation and mismatch

Process Variation and Mismatch

ION,min needed

by the sense

amplifier

V should be > 0

for proper sensing

upsize

ION

VSA

CLB

(Stack)

CP

SA

Root

Input

ION

VSA

IOFF


Sizing for yield

CBL

CP

CBL

DCVSL-SA

DCVSL-SA

CP

Sizing for Yield

Leakage Current

EDP

  • Yield Target: 99% (Monte Carlo process and mismatch simulations)

  • needs to be verified in silicon


Constant yield lines

Solid line has a 99% yield over all process corners.

Overkill?

The yield increases as VDD increases

Constant Yield Lines

CP (Upsized)

CLB: 10x

CP Sense Amp: 2x

EDP CP

Performance

Loss

CP


Constant yield lines1

Dash-dotted line represents a constant Yield Line.

Size of CLB tailored to desired Yield and VDD.

Constant Yield Lines

CP (Upsized)

CLB: 10x

CP Sense Amp: 2x

EDP CP

B

99% yield line

A

CP

YieldB = YieldA


Constant yield lines2

Constant Yield Lines

CP (Upsized)

CLB: 10x

CP Sense Amp: 2x

Upsized EDP

EDP CP

B

99% yield line

CP

A

CMOS

CP

TG

YieldB = YieldA


Constant yield lines3

Constant Yield Lines

Upsized EDP

CBL (Upsized)

EDP CBL

CBL

B

CBL 99% line

CP

A

CBL

CMOS

TG

YieldB = YieldA


Constant yield lines4

Constant Yield Lines

Upsized EDP

EDP

CBL

DCVSL-SA (Upsized)

CP

B

DCVSL-SA 99% line

CMOS

A

DCVSL-SA

TG

DCVSL-SA

YieldB = YieldA


Edp and yield

EDP

(w/o sizing for yield)

EDP

(constant yield)

CBL

CBL

CP

CP

CMOS

CMOS

TG

TG

DCVSL-SA

DCVSL-SA

EDP and Yield


Edp and yield1

EDP

(w/o sizing for yield)

EDP

(constant yield)

CBL

CBL

CP

CP

CMOS

CMOS

TG

TG

DCVSL-SA

DCVSL-SA

EDP and Yield

High Voltage Space


Summary of results

EDP

(constant yield)

CBL

Leakage

Current

CMOS

CP

CBL

CMOS

DCVSL-SA

TG

TG

CP

DCVSL-SA

Summary of Results

  • DCVSL-SA best performing SA, and competitive with current TG and CMOS implementations.

    However…

  • More difficult to design

    • Analog-like design process

  • Less versatile

    • Mandatory latch at the output

    • DVS

  • Higher design risk

    • 6 unacceptable


Summary of results1

Summary of Results

  • DCVSL-SA best performing SA, and competitive with current TG and CMOS implementations.

    However…

  • More difficult to design

    • Analog-like design process

  • Less versatile

    • Mandatory latch at the output

    • DVS

  • Higher design risk

    • 6 unacceptable


Sense amplifiers in future technologies

Sense Amplifiers in Future Technologies

  • Design of Sense Amplifiers in the future will become more challenging.

    • Impact of process variations will become more pronounced

    • VDD will continue to scale

      • VSA/VDD increases

      • VTH/VDD increases

  • The useful design space will be limited.

    • Low leakage environments

    • High voltage, low energy space


Thank you

Thank you


Design considerations in clbs for deep sub micron technologies1

Design Considerations in CLBs for Deep Sub-Micron Technologies

Louis Alarcon

Octavian Florescu


Energy delay

Energy – Delay

CP

CBL

CP

CBL

CMOS

TG

DCVSL-SA

DCVSL-SA


Low threshold voltage

CBL

CP

TG

CMOS

DCVSL-SA

Low Threshold Voltage


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