Multi-mode power amplifier with low gain variation over temperature
First Claim
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.
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Abstract
A multi-mode RF amplifier is described having at least a higher and a lower power path coupling an input to an output. At a pre-selected output power level, the higher power path is enabled while the lower power path is disabled when more output power is required. The process is reversed when less power is needed. The present invention matches the power gain variation over temperature characteristic of each path such that, especially at the cross over point, the gain delta (the difference in power gain between the two paths) has minimal variation over temperature. Such power gain characteristic is required for meeting the test requirements, specifically the inner loop power control, for third generation (3G) cellular handsets.
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Citations
18 Claims
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1. A multi-mode amplifier defining an input and an output, the multi-mode amplifier comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for amplifying a signal traveling through a multi-mode amplifier from an input to an output, the method comprising the steps of:
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first transferring the input to the output via a higher power transistor, wherein when temperature increases the power gain of the higher power transistor decreases; increasing the DC collector current of the higher power transistor as the temperature rises, partially compensating for the decrease in power gain with rising temperature; second transferring, in parallel with the first transferring, the input to the output via a lower power transistor, wherein when the temperature increases the power gain of the lower power transistor decreases; and decreasing the DC collector current of the lower power transistor as the temperature rises, further decreasing the power gain of the lower power transistor, wherein the magnitude of decrease in power gain of the higher power transistors (approximately) matches the magnitude of decrease in power gain of the lower power transistor. - View Dependent Claims (8, 9)
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10. A multi-mode amplifier comprising:
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means for first transferring the input to the output via a higher power transistor, wherein the power gain of the higher power transistor decreases with rising temperature; means for increasing the power gain of the higher power transistor by increasing the DC collector current of the higher power transistor when the temperature rises, partially compensating for the decrease in power gain with rising temperature; means for second transferring, in parallel with the first transferring, the input to the output via a lower power transistor; and means for decreasing the power gain of the lower power transistor by decreasing the DC collector current of the lower power transistor with rising temperature, wherein the magnitude of decrease in power gain of the higher power transistor (approximately) matches the magnitude of decrease in power gain of the lower power transistor with rising temperature. - View Dependent Claims (11, 12, 13)
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14. A multi-mode amplifier defining an input and an output, the amplifier comprising:
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a higher power path comprising a higher power transistor and a first bias circuit providing and controlling DC collector current of the higher power transistor; a lower power path comprising a lower power transistor and a second bias circuit providing and controlling DC collector current of the lower power transistor; and wherein the first bias circuit provides that the DC collector current of the higher power transistor increases with temperature, and wherein the second bias circuit provides that the DC collector current of the lower power transistor decreases with temperature, wherein the higher power path exhibits a reduced power gain variation with temperature, and the lower power path exhibits an increased power gain variation with temperature that matches the power gain variation with temperature of the higher power transistor. - View Dependent Claims (15, 16, 17)
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18. A multi-mode power amplifier having an input and an output, the muulti-mode amplifier comprising:
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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 reference current arranged in a first bias circuit configured to provide a first base current to the higher power transistor, wherein the DC collector current of the higher power transistor is a mirror of the first reference current, and wherein the DC collector current of the higher power transistor rises 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 reference current arranged in a second bias circuit configured to provide a second base current to the lower power transistor, wherein the DC collector current of the lower power transistor is a mirror of the second reference current, and wherein second reference current is at least four times lower than the first reference current such that the DC collector current of the lower power transistor decreases with rising temperatures, and 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.
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Specification