Clockless Chips
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Transcript Clockless Chips
Clockless Chips
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Presentation flow:
Introduction.
Problems with synchronous circuits.
Clockless / Asynchronous circuits.
How clockless chips work?
Simplicity in design.
Applications.
Applications (technical perspective).
Challenges.
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Introduction.
Struggle for the improvement in the microprocessor’s
performance/functioning.
– Pipelining
– (Simultaneous) Multi-threading
}
Synchronous
– Clockless / Asynchronous logic
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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%).
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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.
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Clock time cycle vs. clockless time cycle
Courtesy: Fulcrum Microsystems.
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Courtesy: Computers without clocks – Ivan E Sutherland and Jo Ebergen
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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.
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Simple and efficient design
No centralized clock required.
Standardized components can be used.
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Some features
Integrated pipelining mode.
– Domino logic.
– Delay – insensitive.
Two different implementation details
– Dual rail.
– Bundled data.
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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).
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Advantages (technical look)
Asynchronous for higher
performance:
– Data-dependent delays.
– All carry bits need to be
computed.
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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
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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.
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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.
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Advantages (technical look)…
Heterogeneous Timing:
– Gate delays.
– Interconnection delays.
– Heterogeneous systems
would increase the delays in
the circuits.
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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.
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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_0
1_2001.html
http://www.technologyreview.com/articles/01/10/tristram1001.asp
http://www1.cs.columbia.edu/async/misc/economist/Economist_c
om.htm
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Thank you
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