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A METHODOLOGY TO STORE AND RECYCLE ENERGY IN A CIRCUIT

IP.com Disclosure Number: IPCOM000008518D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-19
Document File: 4 page(s) / 197K

Publishing Venue

Motorola

Related People

Aurobindo Dasgupta: AUTHOR [+2]

Abstract

In this paper, we present a novel concept of "energy recycling" within a circuit. Energy which is normally discharged, is "stored" and used in subse- quent clock cycles. This "stored" energy, is used to partially precharge rising (0 + 1) nodes in the circuit. These partially precharged nodes, consume a smaller amount of charge from the power supply. For example, up to 87.5% savings in energy can be obtained on a 16 bit data bus, with 8 storage capaci- tances. The energy savings are approximately 45% more than the technique in [l] which uses energy recovery and no energy storage.

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MOTOROLA Technical Developments

A METHODOLOGY TO STORE AND RECYCLE ENERGY IN A CIRCUIT

by Aurobindo Dasgupta and Shantanu Ganguly

ABSTRACT

  In this paper, we present a novel concept of "energy recycling" within a circuit. Energy which is normally discharged, is "stored" and used in subse- quent clock cycles. This "stored" energy, is used to partially precharge rising (0 + 1) nodes in the circuit. These partially precharged nodes, consume a smaller amount of charge from the power supply. For example, up to 87.5% savings in energy can be obtained on a 16 bit data bus, with 8 storage capaci- tances. The energy savings are approximately 45% more than the technique in [l] which uses energy recovery and no energy storage.

1 INTRODUCTION

  In the proposed approach, energy is recycled by storing it on "storage" capacitances within the circuit. Energy is stored in the form of charge and is subsequently used to decrease the total energy consumed. In contrast to adiabatic switching "energy recycling" does not draw all of the required energy from the power supply.

2 ENERGY RECYCLING-THE CONCEPT

   Consider a data bus with W bit-lines (with identical capacitance C) of which A4 are falling (1 + 0) and N are rising (0 + 1). The total energy consumed by the bus is the energy required to charge the N rising bit-lines and is given as Ec~niTI.e

                 = N l C l V'M. On the other hand, the energy discharged by the A4 falling bit-lines is EM,,,, = M l C l V'm.

  In contrast to energy recovery [I], energy recycling stores the energy dissipated from falling bit-lines on storage capacitances. This stored energy is subsequently used to "partially precharge" the rising bit-lines before charging them to VU. Using this energy recycling technique it is possible to signif- icantly decrease the energy dissipated on a data bus.

2.1 ENERGY RECYCLING- THE IMPLEMENTATION

  In Figure 1, the storage capacitances are used to store energy that is otherwise discharged in a circuit. The energy consumed is minimized by min- imizing the charge drawn from the power supply. This is accomplished by maximizing the charge that is recycled (i.e. minimize the usage of the stored charge).

I Con*rol circuit

Fig. 1 The circuitry for the proposed charge storage and recovery algorithm.

  The optimal algorithm for charge transfers between the rising bit lines, falling bit lines and storage capacitances, is given in Figure 2. Finally, the buffers in Figure 1 are enabled so that the partially precharged rising bit lines are charged to

Vdd and the partially discharged falling bit lines are fully discharged. The bit-line capacitances are not

  Research in energy recovery [I] involved trans- ferring some charge from the falling bit-lines (I + 0) to the rising bit-lines (0 -+ 1). This technique has been shown to achieve up to 80% savings of energy for a 64 bit data bus.

R Matorda. Inc. I997 173 December 1997

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MOTOROLA Technical Developments

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