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Browse Prior Art Database

METHOD OF IMPROVED RF PERFORMANCE AND INTERNAL CHARGER PERFORMANCE

IP.com Disclosure Number: IPCOM000009425D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-22
Document File: 4 page(s) / 143K

Publishing Venue

Motorola

Related People

Wayne Ballantyne: AUTHOR [+3]

Abstract

Wireless subscriber radios often use recharge- able batteries as the primary energy source. Such batteries are typically charged with an external charger that comprises all the hardware and software required to perform that function. In order to mini- mize the size of the charger and reduce cost while providing simple operation to the end user, there is a trend to include most of the charger components in the subscriber radio. This is commonly referred to as a built in charger. In some of the earlier imple- mentations of such mini-chargers, however, radio cost and RF performance was compromised. The invention provides a configuration for a built in charger that does not compromise transmitter per- formance and maintains all the desired charging features.

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Developments Technical 0 M MOTOROLA

METHOD OF IMPROVED RF PERFORMANCE AND INTERNAL CHARGER PERFORMANCE

by Wayne Ballantyne, Joseph Patiiio and Gus Leizerovich

  Wireless subscriber radios often use recharge- able batteries as the primary energy source. Such batteries are typically charged with an external charger that comprises all the hardware and software required to perform that function. In order to mini- mize the size of the charger and reduce cost while providing simple operation to the end user, there is a trend to include most of the charger components in the subscriber radio. This is commonly referred to as a built in charger. In some of the earlier imple- mentations of such mini-chargers, however, radio cost and RF performance was compromised. The invention provides a configuration for a built in charger that does not compromise transmitter per- formance and maintains all the desired charging features.

  The Block diagram of prior art is shown in Figure 1. The main issue with this configuration is that the current feeding the transmitter RF power amplifier flows across the FET SWITCH. The volt- age drop across this FET SWITCH reduces the available voltage for the transmitter power amplifi- er, therefore a larger device is required in the PA to provide the same amount of RF power and at the same time energy is being wasted decreasing overall

transmitter efficiency which has a direct impact on subscriber talktime. To provide a reference, the FET SWITCH used in the StarTac phone is the Siliconix SI9424DY. Its Rds in the on state is 33 milliohms when 2.5V is applied between the gate and the source. An iDEN 3.6V transmitter has a peak current of approximately 2A. The voltage drop will then be 66 mV which corresponds to a drop in TX output power of 0.17 dB as measured on the Eagle PO board which uses the GSM StarTac TX power amplifier.

  Another drawback of the FET is that additional B+ noise is introduced as a result of the PA current flowing through a larger resistance. This noise, which has multiple frequency components depend- ing on the TDMA rate and symbol rate, is applied to all other circuits in the radio with a B+ connection. In particular, the noise passes through to the regulat- ed supply voltages due to the finite power supply rejection ratio of the regulators used to generate these voltages. Once the noise is on these regulated supplies, critical IC parameters such as synthesizer phase noise, synthes...