NTU Confidential

Introduction to the Introduction to the Applications of Applications of

Asynchronous CircuitsAsynchronous Circuits

Presenter: Po-Chun HsiehAdvisor:Tzi-Dar Chiueh

Date: 2003/09/22

2NTU Confidential

OutlineOutline• Asynchronous Circuits Review• Applications - High-Speed - Low-Power - Low Noise and Low Emission - Heterogeneous Systems• Conclusion• Reference

3NTU Confidential

Asynchronous Circuits Review Asynchronous Circuits Review (1/4)(1/4)

ComputationUnit

ComputationUnit

ACKNOWLEDGE

REQUEST

DATA

Synchronous Asynchronous

ComputationUnit

ComputationUnit

CLOCK

DATA

4NTU Confidential

Asynchronous Circuits Review Asynchronous Circuits Review (2/4)(2/4)

UnderHowto dothe

Homework

Finishthe

Homework

Writethe

ReportData Data

Bill JohnAndy

HW

12:00 am 12:00 am 12:00 am 12:00 am

Data

UnderHowto dothe

Homework

Finishthe

Homework

Writethe

Report

Data Data

Mail Mail

Bill JohnAndy

HW

12:00 am 09:00 am 06:00 am 03:00 am

Synchronous

Asynchronous

5NTU Confidential

Asynchronous Circuits Review Asynchronous Circuits Review (3/4)(3/4)

Previous ComputationB

ComputationA

Handshakecircuit

Rin Rout

Aout Ain

ComputationUnit

Reg

Rin

Aout

Rout

Ain

Rin Rout

AinAout

6NTU Confidential

Asynchronous Circuits Review Asynchronous Circuits Review (4/4)(4/4)

• Benefits:– No global clock to distribute– Early completion (Data-dependent delays and

Stage-dependent delays)– Low Power

• Drawbacks:– There are not many asynchronous tools– Not easy to test – Area cost

NTU Confidential

Applications for High-Speed Applications for High-Speed CircuitsCircuits

8NTU Confidential

Average-Case delayAverage-Case delay

[4]

9NTU Confidential

Single-Rail vs. Dual-Rail Protocol (1/2)Single-Rail vs. Dual-Rail Protocol (1/2)

• Single-Rail： Bounded delay, not easy to do early completion detection.• Sometimes we can use multi-case delay

FunctionData Data

delay

Function Data

delay

10

NTU Confidential

Single-Rail vs. Dual-Rail Protocol (2/2)Single-Rail vs. Dual-Rail Protocol (2/2)

• Dual-Rail: Encode every signal, Xi, with two wires, Xi,H and Xi,L

[1]

A,H

A,L

B,H

B,L

A,H

A,L

B,H

B,L

C,H=A,H+B,H

C,L=A,L*B,L

[2]

11

NTU Confidential

Multi-case delay look-ahead Multi-case delay look-ahead adderadder

[3]

12

NTU Confidential

Dual-rail circuitsDual-rail circuits

• Differential Cascode Voltage Switch Logic (DCVSL)• Reduced direct logic (RDL)

13

NTU Confidential

Dual-rail AdderDual-rail Adder

[4]

• A. Martin (1991)• Asynchronous adder transistor count =34

14

NTU Confidential

ComparisonComparison

Bounded delay Dual-rail

Area Better Worse

Early Completion Worse Better

Power Better ? Worse ?

NTU Confidential

Low-Power CircuitsLow-Power Circuits

•No global clock•Functions work only when needed

16

NTU Confidential

Dissipating when and where Dissipating when and where activeactive

• Functions work only when needed• In Synchronous systems, we may use Gated

ClockA input 16bits B input 16bitsOperator 2 bits

Exponent Operationcomepare

Smaller Biger

Shift Right

Multiplier & Divider

Adder & Subtractor

MUX21 Array X12

MUX21 X5

MUX21 Array

Exponent of A or B

Adder_Subtractorexponent

Exponent of Sum

Control Unit

NTU Confidential

Low Noise and Low EmissionLow Noise and Low Emission

18

NTU Confidential

What speed clock bringsWhat speed clock brings

• Noise• When voltage drops

across parasitic inductances emit EM wave

[1]

L

High frequencyCurrent

largevoltagevariation

19

NTU Confidential

• Frequency spectra of the two 80C51 microcontrollers

• In synchronous circuit with 3.6 MHz clock rate, there are a series of harmonics

[1]

NTU Confidential

Heterogeneous Systems (GALS)Heterogeneous Systems (GALS)

21

NTU Confidential

Globally-Asynchronous Globally-Asynchronous Locally-SynchronousLocally-Synchronous

• Synchronous Circuits are easy to design• Low Power: No PLL, No clock driver, Functions

work only when needed.• An approach for System-on-Chip timing

Synchronous System

Asynchronous

Synchronous System

Asynchronous

Synchronous System

Asynchronous

Mpegdecoder IP Modem Antenna

Memory

A/D

USB

CPU

22

NTU Confidential

Synchronous-Asynchronous Synchronous-Asynchronous interfaces interfaces

– asynchronous wrapper– asynchronous wrapper• h

23

NTU Confidential

ConclusionConclusion• Due to average-case delay, asynchronous

circuits have high performance.• No clock driver, No high-speed oscillator, No

PLL, and the Functions work only needed, asynchronous circuits have low power dissipation.

• No global clock No high frequency current component Low Noise and Low EM wave emission

• Due to the Increasing reuse of building blocks (IP), and integration of entire system, heterogeneous systems may be well used in the future.

24

NTU Confidential

ReferenceReference

[1] Scanning the Technology:Applications of asynchronous circuitsC. H. (Kees) van Berkel, Mark B. Josephs, and Steven M. Nowick. Proceedings of the IEEE, 87(2):223--233, February 1999.[2] Designing asynchronous circuits for low power: An IFIR filter bank for a digital hearing aidL. S. Nielsen and J. Sparsø, this issue, pp. 268-281.[3] VLSI circuits for low-power high-speed asynchronous addition S.Perri, P.Corsonello, G. Cocorullo; IEEE Trans. On VLSI Systems, In Press 2002 [4] The systematic Design of asynchronous circuits

ICCA 95[5] An asynchronous low-power 80c51 microcontrollerH. van Gageldonk, D. Baumann, K. van Berkel, D. Gloor, A. Peeters, and G. Stegmann,in Proc. Int. Symp. Advanced Researchin Asynchronous Circuits and Systems, 1998, pp. 96–107.