Patent ID: 7554407
Filing Date: 2009-06-30
Classification: H03F

Abstract:
1. A multi-mode amplifier defining an input and an output, the multi-mode amplifier comprising: a first higher power amplifier transferring the input to the output, the first higher power amplifier comprising a higher power transistor arranged to provide an increased power gain when its DC collector current is increased and a reduced power gain with rising temperature; a first bias circuit configured to provide a first base current to the higher power transistor, wherein the first base current increases when temperature increases, wherein the rate of increase in the first base current is higher than the rate of decrease in DC current gain of the higher power transistor with rising temperature and, hence, increases the DC collector current of the higher power transistor at higher temperatures, but wherein the result is a decrease in power gain with rising temperature; a second lower power amplifier in parallel with the first higher power amplifier, the second lower power amplifier comprising a lower power transistor arranged to provide a reduced power gain when its DC collector current is decreased and a reduced power gain with rising temperature; and a second bias circuit configured to provide a second base current to the lower power transistor, wherein, although the second base current increases with rising temperature, the rate of increase in the second base current is lower than the rate of decrease in DC current gain of the lower power transistor with rising temperature and, hence, decreases the DC collector current of the lower power transistor at higher temperatures, wherein the result is a decrease in power gain with rising temperature, and wherein the magnitude of decrease in power gain of the higher power amplifier approximately matches the magnitude of decrease in power gain of the lower power amplifier when the temperature rises.