1. Clockless Chips Date: October 26, 2005. Presented by:
K. Subrahmanya Sreshti.
(05IT6004)
School of Information Technology
Indian Institute of Technology, Kharagpur

2. Presentation on Clockless Chips
Presentation flow:
Introduction.
Problems with synchronous circuits.
Clockless / Asynchronous circuits.
How clockless chips work?
Simplicity in design.
Applications.
Applications (technical perspective).
Challenges.
October 26, 2005
Presentation on Clockless Chips

3. Presentation on Clockless Chips
Introduction.
Struggle for the improvement in the microprocessor’s performance/functioning.
Pipelining
(Simultaneous) Multi-threading
Clockless / Asynchronous logic
}Synchronous
October 26, 2005
Presentation on Clockless Chips

4. Problems with Synchronous Approach
Distributing the clock globally.
Wastage of energy.
Traverse the chip’s longest wires in one clock cycle.
Order of arrival of the signals is unimportant.
Clocks themselves consume lot of energy (~30%).
October 26, 2005
Presentation on Clockless Chips

5. Presentation on Clockless Chips
Synchronous circuit
Longest path determines the minimum clock period.
Dissipation of energy for each clock cycle.
EMI is more in synchronous elements.
October 26, 2005
Presentation on Clockless Chips

6. Clockless chips (Asynchronous logic circuits)
Colckless chips/Asynchronous/self-timed circuits.
Functions away from the clock.
Different parts work at different speeds.
Hand-off the result immediately.
October 26, 2005
Presentation on Clockless Chips

7. Clock time cycle vs. clockless time cycle
Courtesy: Fulcrum Microsystems.
October 26, 2005
Presentation on Clockless Chips

8. Courtesy: Computers without clocks – Ivan E Sutherland and Jo Ebergen
October 26, 2005
Presentation on Clockless Chips

9. Presentation on Clockless Chips
How do they work?
No pure asynchronous chips are available.
Uses handshake signals for the data exchange.
Data moves only when required, not always.
Minimizes power consumption.
Less EMI  less noise  more applications.
Stream data applications.
October 26, 2005
Presentation on Clockless Chips

10. Simple and efficient design
No centralized clock required.
Standardized components can be used.
October 26, 2005
Presentation on Clockless Chips

11. Presentation on Clockless Chips
Some features
Integrated pipelining mode.
Domino logic.
Delay – insensitive.
Two different implementation details
Dual rail.
Bundled data.
October 26, 2005
Presentation on Clockless Chips

12. Presentation on Clockless Chips
Advantages
Works at its average speed.
Low power consumption.
Twice life-time.
Less heat generated.
 Good to mobile devices.
Less EMI  less noise  more applications.
Smart cards (due to asynchronous nature).
October 26, 2005
Presentation on Clockless Chips

13. Advantages (technical look)
Asynchronous for higher performance:
Data-dependent delays.
All carry bits need to be computed.
October 26, 2005
Presentation on Clockless Chips

14. Advantages (technical look)…
Asynchronous for low power:
Consumes power only when and where active.
Rest of the time returns to a non-dissipating state, until next activation.
Illustrated through frequency divider
October 26, 2005
Presentation on Clockless Chips

15. Advantages (technical look)…
Asynchronous for low power:
Almost fixed power dissipation is achieved.
Many applications such as:
Infrared communication receiver.
Filter bank for digital hearing.
In pagers.
Double battery life.
October 26, 2005
Presentation on Clockless Chips

16. Advantages (technical look)…
Asynchronous for low noise and low emission:
Digital sub-circuits
Generates voltage noise (on power lines)
Induces current on silicon substrate.
Emits electromagnetic radiation at its clock frequency or its harmonics.
October 26, 2005
Presentation on Clockless Chips

17. Advantages (technical look)…
Heterogeneous Timing:
Gate delays.
Interconnection delays.
Heterogeneous systems would increase the delays in the circuits.
October 26, 2005
Presentation on Clockless Chips

18. Presentation on Clockless Chips
Challenges
Interfacing between synchronous and asynchronous
Many devices available now are synchronous in nature.
Special circuits are needed to align them.
Lack of expertise.
Lack of tools.
Engineers are not trained in these fields.
Academically, no courses available.
October 26, 2005
Presentation on Clockless Chips

19. Presentation on Clockless Chips
References
Scanning the Technology: Applications of Asynchronous Circuits – C. H. (Kees) van Berkel, Mark B. Josephs, and Steven M. Nowick
Computers without clocks – Ivan E Sutherland and Jo Ebergen.
(October 2001)
October 26, 2005
Presentation on Clockless Chips

20. Presentation on Clockless Chips
Thank you
October 26, 2005
Presentation on Clockless Chips