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AC FREQUENCY MINIMUM-AMPLITUDE DEVICE-TYPE DETECTION METHOD

IP.com Disclosure Number: IPCOM000006448D
Original Publication Date: 2002-Jan-03
Included in the Prior Art Database: 2002-Jan-03
Document File: 3 page(s) / 236K

Publishing Venue

Motorola

Related People

Kuek Teck Hock: AUTHOR

Abstract

AC FREQUENCY MINIMUM-AMPLITUDE DEVICE-TYPE DETECTION METHOD

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AC frequency minimum-amplitude device-type detection method

Kuek Teck Hock

Introduction

Cellular telephones typically use direct current (DC) level detection for identifying plug-in accessories such as battery chargers. DC level detection uses an Identifier (ID) resistor built in the accessory as illustrated in diagram 1.  The DC voltages at an Analog to Digital Converter (ADC) input will vary depending upon the ID resistor value associated with a specific accessory type.  Accordingly, voltage ranges at the ADC input identify the accessory type. There are a small number of voltage ranges that are used in DC level detection due to resistor and power supply accuracy’s, therefore the number of accessory types that can be identified is also small.  This paper describes an economical AC frequency minimum-amplitude device-type detection method that allows for detection of many accessory types.

Description of operation

An AC frequency minimum-amplitude device-type detection method was developed and uses a detection circuit as shown in Diagram 2. The ID component in the accessory has a series configured LC network comprising an inductor L and a capacitor C. The constant amplitude AC signal generator provides a current flow to the ID component and the voltage across R2 is be detected by the ADC circuit.

The AC signal generator provides different frequencies of constant amplitude as shown in Diagram 3. Although only three frequencies are illustrated, in practice ten are more frequencies are provided. The ADC detector input signal at R2 may typically look like that as illustrated in diagram 4.


In each type of accessory, the series configured LC network has a resonance frequency (Fr) t...