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Maximization of Shelf Life for a Battery-Powered Computer

IP.com Disclosure Number: IPCOM000061736D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Arroyo, RX: AUTHOR [+2]

Abstract

A battery-powered computer requires that memory contents in both the main memory and display buffer be retained when the computer is not in use (powered off). The Real Time Clock must also continue to function in this state. This requires some of the logic components of the computer to stay powered on, even when the system itself is off. The battery drain required to support these functions is reduced to a minimum by using three techniques. These are component selection, power system control, and proper interfacing to the powered-on devices for minimum power drain. The components remaining powered on when the computer is off are the main memory, display buffer memory, power supply control logic and the Real Time Clock.

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Maximization of Shelf Life for a Battery-Powered Computer

A battery-powered computer requires that memory contents in both the main memory and display buffer be retained when the computer is not in use (powered off). The Real Time Clock must also continue to function in this state. This requires some of the logic components of the computer to stay powered on, even when the system itself is off. The battery drain required to support these functions is reduced to a minimum by using three techniques. These are component selection, power system control, and proper interfacing to the powered-on devices for minimum power drain. The components remaining powered on when the computer is off are the main memory, display buffer memory, power supply control logic and the Real Time Clock. CMOS technology was chosen for all of these parts because of the capability of CMOS to draw very low standby current when there are no (or few) logic state transitions. Static memory was chosen so that there would be no refresh requirement to maintain memory contents. This eliminates any need for logic activity to maintain memory. The CMOS Real Time Clock module is operated at its lowest specified frequency. This reduces the number of transitions of this part to the minimum, thereby reducing its power requirements. The power supply control logic was designed to require no clocks to power the machine on. This allows the oscillator normally driving this part to be powered off with the computer, so that transitions are reduced to zero. Power transitions on semiconductor components can cause glitches at their outputs. Components remaining powered while other components that they are connected to are undergoing power transitions must be insulated from the effect of t...