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Energy-Efficient Circuit Design

Nugent, Michael (2015) Energy-Efficient Circuit Design. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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We initiate the theoretical investigation of energy-efficient circuit design.
We assume that the circuit design specifies the circuit layout as well as the
supply voltages for the gates. To obtain maximum energy efficiency, the circuit
design must balance the conflicting demands of minimizing the energy used per gate,
and minimizing the number of gates in the circuit; If the energy supplied to the
gates is small, then functional failures are likely, necessitating a circuit layout
that is more fault-tolerant, and thus that has more gates.

By leveraging previous
work on fault-tolerant circuit design, we show general upper and lower bounds on
the amount of energy required by a circuit to compute a given relation. We show
that some circuits would be asymptotically more energy-efficient if heterogeneous
supply voltages were allowed, and show that for some circuits the most energy-efficient
supply voltages are homogeneous over all gates.

In the traditional approach to circuit design the
supply voltages for each transistor/gate are set sufficiently high so that with
sufficiently high probability no transistor fails.
We show that if there is a better (in terms of worst-case relative error with respect to energy) method than the traditional approach
then $P=NP$,
and thus there is a complexity theoretic obstacle to achieving energy savings with Near-Threshold computing.

We show that almost all
Boolean functions require circuits that use exponential energy. This is not an immediate
consequence of Shannon's classic result that most functions require exponential
sized circuits of faultless gates because, as we show, the same circuit layout can
compute many different functions, depending on the value of the supply voltage.

If the error bound must vanish as the number of inputs increases, we show that a natural class of functions can be computed with asymptotically less energy using heterogeneous supply voltages than is possible using homogeneous supply voltages.
We also prove upper bounds on the asymptotic energy savings achieved by using heterogeneous supply voltages over homogeneous supply voltages for a class of functions, and also show a relation that can bypass this bound.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Nugent, Michaelmpn1@pitt.eduMPN1
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairPruhs, Kirkkirk@cs.pitt.eduKRP2
Committee MemberMossé, Daniel
Committee MemberLee, Adam J
Committee MemberGupta, Anupam
Date: 27 September 2015
Date Type: Publication
Defense Date: 29 April 2015
Approval Date: 27 September 2015
Submission Date: 9 July 2015
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 98
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Computer Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Energy Efficiency, Circuit Design, Near-Threshold Computing
Date Deposited: 27 Sep 2015 23:22
Last Modified: 15 Nov 2016 14:29


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