Browse Prior Art Database

Method of Controlling Backlights in a Phone with a Keypad and a Touchscreen Display

IP.com Disclosure Number: IPCOM000020681D
Original Publication Date: 2003-Dec-08
Included in the Prior Art Database: 2003-Dec-08
Document File: 3 page(s) / 34K

Publishing Venue

Motorola

Related People

Robert Johnson: AUTHOR

Abstract

This paper describes a method of controlling the backlighting in a phone which has both a keypad and a touchscreen type display. In applications where input can be done by either method or in applications where input can only be done by one method or another, this methodology allows some backlighting to be turned off. Thus significant power reduction can be achieved in an automatic fashion.

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Title: Method of Controlling Backlights in a Phone with a Keypad and a Touchscreen Display.

Author: Bob Johnson

Abstract:

This paper describes a method of controlling the backlighting in a phone which has both a keypad and a touchscreen type display. In applications where input can be done by either method or in applications where input can only be done by one method or another, this methodology allows some backlighting to be turned off. Thus significant power reduction can be achieved in an automatic fashion.

Problem Statement:

Backlighting currents are very high as compared to the current consumed by phones in their standby mode. Many phones are utilizing Color Displays which must be backlit by White LEDs otherwise the colors will not be true. White LED’s have the special problem of having high forward voltages, typically in the range of 3.5 volts causing boost power supplies to be used for them. A single LED at 15 mA will typically consume 20 mA from the phone’s battery. Multiply this by 4 for the keypad and 3 for the display, and you have 140 mA. Typical standby currents for GSM phones in the 2004 timeframe will be on the order of 1 to 2 mA. Thus 60 seconds of backlights will be equivalent to 70 to 140 minutes of standby.

There is a profound need in phones to minimize the backlight currents without negatively affecting the end user’s experience while using their phone.

Smart phones will utilize both touch displays and will contain keypads for text entry. These func...