Browse Prior Art Database

HIGH EFFICIENCY RF AMPLIFIER WITH MULTIPLE OUTPUT POWER LEVELS

IP.com Disclosure Number: IPCOM000005978D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
Document File: 2 page(s) / 82K

Publishing Venue

Motorola

Related People

Kazimierz Siwiak: AUTHOR

Abstract

This invention is an RF power amplifier capable of energy efficient operation at several selectable output power levels. Radio Frequency amplifiers, especially those in portable transceivers, do nd maintain efficiency under reduced RF output conditions. Maintaining efficiency with RF output power cutback is a key require- ment for radios that are designed to save battery energy as a result of reduced power operation. One radio which used an RF PA with power cutback capability is the SABER UHF portable transceiver. That radio draws 1900 mA at 75 volts for a power output of 2 watts. The efficiency is 14.0%. When the power is cut back to 0.25 watts, the transmitter current is 1200 mA at 75 volts for an efficiency of only 2.6%. It can be seen that the transmitter efficiency has degraded by a factor of 14/2.6 = 5 for a 9 dB cutback in RF output power. The battery current due to a 9 dB cutback reduces by just 37% for an 66% reduction in output power. Clearly, power cutback on a SABER type PA will not significantly impact battery energy savings.

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MOTOROLA Technical Developments Volume 11 October 1990

HIGH EFFICIENCY RF AMPLIFIER WITH MULTIPLE OUTPUT POWER LEVELS

by Kazimierz Siwiak

   Background of invention: This invention is an RF power amplifier capable of energy efficient operation at several selectable output power levels. Radio Frequency amplifiers, especially those in portable transceivers, do nd maintain efficiency under reduced RF output conditions. Maintaining efficiency with RF output power cutback is a key require- ment for radios that are designed to save battery energy as a result of reduced power operation. One radio which used an RF PA with power cutback capability is the SABER UHF portable transceiver. That radio draws 1900 mA at 75 volts for a power output of 2 watts. The efficiency is 14.0%. When the power is cut back to 0.25 watts, the transmitter current is 1200 mA at 75 volts for an efficiency of only 2.6%. It can be seen that the transmitter efficiency has degraded by a factor of 14/2.6 = 5 for a 9 dB cutback in RF output power. The battery current due to a 9 dB cutback reduces by just 37% for an 66% reduction in output power. Clearly, power cutback on a SABER type PA will not significantly impact battery energy savings.

This invention provides an RF power amplifier circuit which maintains high efficiency for more than one RF output power level. It also provides a method of selecting RF output power levels under logic control.

   One embodiment of an RF power amplifier which maintains high efficiency for several output power levels is seen in FIG. 1. Three RF amplifier stages, Al, A2 and A3 are shown coupled through PIN diode switches arranged so that amplifier A3 or both amplifiers A2 and A3 can be bypassed. A biasin...