Clockless Chips

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# Clockless Chips - PowerPoint PPT Presentation

Date: October 26, 2005. Clockless Chips. Presented by: K. Subrahmanya Sreshti. (05IT6004) School of Information Technology Indian Institute of Technology, Kharagpur. Presentation flow:. Introduction. Problems with synchronous circuits. Clockless / Asynchronous circuits.

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Date: October 26, 2005.

### Clockless Chips

Presented by:

K. Subrahmanya Sreshti.

(05IT6004)

School of Information Technology

Indian Institute of Technology, Kharagpur

Presentation flow:
• Introduction.
• Problems with synchronous circuits.
• Clockless / Asynchronous circuits.
• How clockless chips work?
• Simplicity in design.
• Applications.
• Applications (technical perspective).
• Challenges.

Presentation on Clockless Chips

Introduction.
• Struggle for the improvement in the microprocessor’s performance/functioning.
• Pipelining
• Clockless / Asynchronous logic

}Synchronous

Presentation on Clockless Chips

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%).

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.

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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.

Presentation on Clockless Chips

Clock time cycle vs. clockless time cycle

Courtesy: Fulcrum Microsystems.

Presentation on Clockless Chips

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.

Presentation on Clockless Chips

Simple and efficient design
• No centralized clock required.
• Standardized components can be used.

Presentation on Clockless Chips

Some features
• Integrated pipelining mode.
• Domino logic.
• Delay – insensitive.
• Two different implementation details
• Dual rail.
• Bundled data.

Presentation on Clockless Chips

• 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).

Presentation on Clockless Chips

• Asynchronous for higher performance:
• Data-dependent delays.
• All carry bits need to be computed.

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• 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

Presentation on Clockless Chips

• Asynchronous for low power:
• Almost fixed power dissipation is achieved.
• Many applications such as:
• Filter bank for digital hearing.
• In pagers.
• Double battery life.

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• 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.

Presentation on Clockless Chips

• Heterogeneous Timing:
• Gate delays.
• Interconnection delays.
• Heterogeneous systems would increase the delays in the circuits.

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.

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.
• http://ieeexplore.ieee.org/iel5/2/30617/01413111.pdf(October 2001)
• http://csdl2.computer.org/comp/mags/dt/2003/06/d6005.pdf
• http://www1.cs.columbia.edu/async/misc/technologyreview_oct_01_2001.html
• http://www.technologyreview.com/articles/01/10/tristram1001.asp
• http://www1.cs.columbia.edu/async/misc/economist/Economist_com.htm

Presentation on Clockless Chips

Thank you

Presentation on Clockless Chips