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ApplyingApplying Asynchronous Circuits in Asynchronous Circuits in Contactless Smart CardsContactless Smart Cards

Joep Kessels, Torsten Kramer

Gerrit den Besten, Ad Peeters, Volker Timm

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Esprit project DescaleEsprit project Descale

• Period: 1998-1999

• Participants: Philips Semiconductors, MAZ, Philips Research

• Goal: find out advantages of asynchronous circuits in contactless smart cards

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Outline

• Designing asynchronous circuits

• Contactless smart cards

• Applying asynchronous circuits in contactless smart cards

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VLSI programming of Handshake circuitsVLSI programming of Handshake circuits

• Designing asynchronous circuits (handshake circuits)

• in a high level programming language (Tangram)

• using a compiler for translation (transparent)

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Tangram Handshake circuit

Sequential compositionSequential composition

A A; B ; B

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Tangram Handshake circuit

Parallel compositionParallel composition

A || B BA ||

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SynchronousSynchronous versusversus asynchronousasynchronous

Synchronous Asynchronous Consequence

Clock driven Demand driven Less average power

Central clock Distributed Smaller current peaks handshakes Less EM emission

Clock timed Self timed Performance adaptation to supply voltage (1..3 V)

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Contactless smart cardContactless smart card

Tuned circuit:

– Power– Clock– Communication

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Mifare (ISO standard)Mifare (ISO standard)

- Proximity card (10 cm) with two way communication

- Power: few mW; Transaction time: 200 msec

- 70 M cards sold

- Clock: 13.56 MHz; Bitrate: 106 Kbit/sec

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Differences in power characteristicsDifferences in power characteristics

Aspect Batteries Contactless

Minimizing Average PeakPower

Supply Constant Fluctuating Voltage

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Digital CircuitDigital Circuit

• Peripherals:– DES

– RSA

– UART

• Memories:– 2 kbyte RAM (10 nsec)

– 32 kbyte EEPROM (read/write 180/4000 nsec)

– 38 kbyte ROM (30 nsec)

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Power 80C51 in time domainPower 80C51 in time domain

Synchronous Asynchronous

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Power 80C51 in frequency domainPower 80C51 in frequency domain

Synchronous Asynchronous

0 100 200 300 400 MHz 0 100 200 300 400 MHz

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Performance adaptation asynchronous 80C51Performance adaptation asynchronous 80C51

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Descale chipDescale chip

5-layer metal

0.35 m

18 mm2

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Area/Power contactless digital circuitry

Block Area [mm2] Power[%]

RAM 1.2 17

ROM 1.0 27

EEPROM 5.6

Async 1.1 56

Total 8.9 100

Async about 12% of contactless digital circuit area

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Effect asynchronous design

Level Power [%] Area [%]

Standard cell -70 +18

Digital circuit -60 +2

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Power regulatorPower regulator

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Improvements in Tangram Toolset

• Redefinition Tangram– communication through variables

• Use of conventional tools for data-path part– Optimizer & Technology mapper to reduce area (10%)

– Timing analysis tool to tune matching delays (up to 50%)

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Conventional solutionConventional solution

• Synchronous digital circuit with fixed speed– superfluous power thrown away – too little power: transaction is canceled

• Performance 80C51 limited by power received

• Buffer capacitor of several nF (large area)

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Advantages asynchronous designAdvantages asynchronous design

• Maximum performance for power received– power efficiency: factor 2– adaptation property: factor 2

• More robustness and/or smaller buffer capacitor – smaller current peaks– adaptation property

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Conclusion

Results so convincing that

a product is being designed

based on these asynchronous circuits

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Mifare ApplicationsMifare Applications

• Seoul: six million bus cards

• Lufthansa: Frequent Flyers cards

• China: highway toll cards

• Brasil: cards for civil servants

(identification & electronic purse)

• Shell: Mifare technology in car keys

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Modifications in 80C51Modifications in 80C51

• Instruction prefetching

(30% more performance)• Early write completion• Immediate halt signal• Quasi synchronous mode

(performance 50% of free-running mode)

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DES convertor

• Transaction contains up to 10 DES conversions• Software conversion : 10 msec, 30 J• Hardware conversion: 1.25 s, 12 nJ• Area 3,250 GE

- 57% combinational logic

- 35% latches/flipflops

- 8% delay matching and C-elements

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Power 80C51 and DES co-processor @ 3.3VPower 80C51 and DES co-processor @ 3.3V