# Patent

## Title
High efficiency multiple power mode linear radio frequency power amplifier

## Abstract

The embodiments disclosed in the detailed description include a power amplifier having a low power mode amplifier, a medium power mode amplifier, and a high power mode amplifier in communication with a radio frequency (RF) output load. The exemplary embodiments of the power amplifier permit a wireless device to select the most power efficient means to transmit an RF signal based upon the desired output power level.

## Background
RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 13/013,091, entitled “HIGH EFFICIENCY MULTIPLE POWER MODE LINEAR RADIO FREQUENCY POWER AMPLIFIER,” now U.S. Pat. No. 8,324,964, which was filed on Jan. 25, 2011, and which is hereby incorporated herein by reference in its entirety. This application is related to U.S. patent application Ser. No. 12/763,659 filed Apr. 20, 2010.


FIELD OF THE DISCLOSURE
The embodiments disclosed herein are related to improving the average current consumption and talk-times of mobile devices. In particular, the embodiments disclosed herein are related to improved average current consumption of linear power amplifiers in mobile devices.
BACKGROUND
Average current consumption and talk-time are important performance metrics for linear power amplifiers used in mobile devices. Some handset manufacturers desire world class average current and talk-time without the use of a DC-DC converter or analog bias control. Thus, there is a need to develop a linear power amplifier that exhibits good average current consumption characteristics, increases the talk-time of a wireless handset, and without the use of a DC-DC converter or analog bias control.
SUMMARY
Embodiments disclosed in the detailed description relate to a power amplifier having a low power mode amplifier, a medium power mode amplifier, and a high power mode amplifier in communication with a radio frequency (RF) output load. Multiple power mode amplifiers address this need by providing multiple modes of operation that provide efficiency benefit for certain power ranges below the maximum output power range. Techniques that can maximize efficiency of the lower power modes of operation without compromising the efficiency of the highest power mode of operation are attractive, and can provide great benefit to the average current consumption and talk time of the wireless handset. The exemplary embodiment of the power amplifier permits a wireless device to select the most power efficient means to transmit an RF signal based upon the desired output power level.
An exemplary embodiment of the power amplifier includes a high power mode output matching network having a first filter node and a second filter node, wherein the second filter node is coupled to a radio frequency output node. A high power mode output stage may be coupled to the first filter node of the high power mode output matching network, where the high power mode output stage has an enable state and a disable state. A medium power mode output stage may include a first input and a first output, the first output in communication with the radio frequency output node, and where the medium power mode output stage has an enable state and a disable state. A low power mode output stage may include a second input and a second output, where the second output may be in communication with the radio frequency output node, and where the low power mode output stage has an enable state and a disable state. The power amplifier may be configured such that in response to the high power mode output stage being in the disable state, the second filter node of the high power mode output matching network may be configured to present a high impedance to the radio frequency output node. Likewise, the power amplifier may be further configured such that in response to the high power mode output stage being in the enable state, the first filter node of the high power mode output matching network is configured to present a substantially power matched impedance to an output of the high power mode output stage.
Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
FIG. 1 depicts a first exemplary embodiment of a high efficiency multiple power mode linear RF power amplifier.
FIG. 2 depicts an operation for controlling the radio frequency power amplifier of FIG. 1.



DETAILED DESCRIPTION
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
Embodiments disclosed herein relate to a power amplifier having a low power mode amplifier, a medium power mode amplifier, and a high power mode amplifier in communication with a radio frequency (RF) output load. Multiple power mode amplifiers address this need by providing multiple modes of operation that provide efficiency benefit for certain power ranges below the maximum output power range. Techniques that can maximize efficiency of the lower power modes of operation without compromising the efficiency of the highest power mode of operation are attractive, and can provide great benefit to the average current consumption and talk time of the wireless handset. The exemplary embodiment of the power amplifier permits a wireless device to select the most power efficient means to transmit an RF signal based upon the desired output power level.
An exemplary embodiment of the power amplifier includes a high power mode output matching network having a first filter node and a second filter node, wherein the second filter node is coupled to a radio frequency output node. A high power mode output stage may be coupled to the first filter node of the high power mode output matching network, where the high power mode output stage has an enable state and a disable state. A medium power mode output stage may include a first input and a first output, the first output in communication with the radio frequency output node, and where the medium power mode output stage has an enable state and a disable state. A low power mode output stage may include a second input and a second output, where the second output may be in communication with the radio frequency output node, and where the low power mode output stage has an enable state and a disable state. The power amplifier may be configured such that in response to the high power mode output stage being in the disable state, the second filter node of the high power mode output matching network may be configured to present a high impedance to the radio frequency output node. Likewise, the power amplifier may be further configured such that in response to the high power mode output stage being in the enable state, the first filter node of the high power mode output matching network is configured to present a substantially power matched impedance to an output of the high power mode output stage.
With reference to FIG. 1, a radio frequency power amplifier 10 includes a low power mode amplifier 12, a medium power mode amplifier 14, a high power mode amplifier 16, a high power mode output matching network 17, and a controller 18. The controller 18 may be a microprocessor, a microcontroller, a state machine, control logic, a computing mechanism, or a combination thereof. The controller 18 may be in communication with memory or include internal memory to store data and computer program codes to be executed on the controller 18.
The radio frequency power amplifier 10 further includes an input matching circuit 20 and may include a secondary input matching circuit 21. The input matching circuit 20 is configured to receive a radio frequency input 22. The input matching circuit 20 is further configured to provide an output to the respective inputs of the secondary input matching circuit 21 and the high power mode amplifier 16. The output of the secondary input matching circuit 21 is coupled to the inputs of the low power mode amplifier 12 and the medium power mode amplifier 14.
The respective outputs of the low power mode amplifier 12 and the medium power mode amplifier 14 are coupled to the input of an output switch 24. The output of the output switch 24 is coupled to a radio frequency output 26 and the high power mode output matching network 17. The output switch 24 is operatively coupled to the controller 18, which controls the state of the output switch 24 via the output switch control signal 29. The output switch 24 includes an open state and a closed state. The controller 18 places the output switch 24 into an open state when the high power mode amplifier 16 is enabled. The controller 18 places the output switch 24 into a closed state when either the low power mode amplifier 12 or the medium power mode amplifier 14 is enabled.
The high power mode output matching network 17 includes a first filter node 30 coupled to the output of the high power mode amplifier 16. The high power mode output matching network 17 further includes a second filter node 32 coupled to the radio frequency output 26 and the output of the output switch 24. The high power mode output matching network 17 may be configured to present a high impedance to the second filter node 32 when the high power mode amplifier 16 is disabled. The high power mode output matching network 17 may further be configured to present a substantially power matched impedance to the first filter node 30 when the high power mode amplifier 16 is enabled.
As depicted in FIG. 1, the high power mode output matching network 17 includes a high power mode output matching circuit 28 and may include a load impedance switch 34 and a load impedance 36. The inputs of the high power mode output matching circuit 28 and the load impedance switch 34 may be coupled to the first filter node 30. The output of the high power mode output matching circuit 28 may further be coupled to the second filter node 32. The load impedance switch 34 may switchably couple a load impedance 36 to the first filter node 30. The load impedance 36 may be a capacitor. The load impedance switch 34 may be coupled to the controller 18, which controls the state of the load impedance switch 34 via the load impedance switch signal 37. The load impedance switch 34 includes an open state and a closed state. The controller 18 may place the load impedance switch 34 into an open state when the high power mode amplifier 16 is enabled, which permits the high power mode output matching network 17 to present a substantially power matched impedance to the first filter node 30. The controller 18 may place the load impedance switch 34 into a closed state when either the low power mode amplifier 12 or the medium power mode amplifier 14 is enabled. When the load impedance switch 34 is placed into the closed state and the high power mode amplifier 16 is disabled, the parallel combination of the load impedance 36 and the output impedance of the high power mode output stage 64 is transformed by the high power mode output matching circuit 28 to a high impedance load at the second filter node 32 relative to the impedance presented by a load on the radio frequency output 26. As a result, most of the power from either the low power mode amplifier 12 or the medium power mode amplifier 14 is delivered to the impedance presented by the load on the radio frequency output 26.
The low power mode amplifier 12 may include a low power mode switch 38, a low power mode input matching circuit 40, and a low power mode output stage 42. The low power mode switch 38 may be coupled to the output of the secondary input matching circuit 21. The low power mode switch 38 may have an open state and a closed state, which is controlled via the low power mode switch signal 44. The low power mode switch 38 may be configured by the controller 18 to close when the low power mode amplifier 12 is enabled. Otherwise, the controller 18 may be configured to open the low power mode switch 38 when either the medium power mode amplifier 14 or the high power mode amplifier 16 is enabled.
The output of the low power mode switch 38 may also be coupled to the input of the low power mode input matching circuit 40, which provides an output to the low power mode output stage 42. The low power mode output stage 42 may also form the output of the low power mode amplifier 12.
The low power mode output stage 42 may be a linear power amplifier configured to provide power gain to a received radio frequency input. The low power mode output stage 42 may include a low power mode enable signal 46 coupled to the controller 18. The low power mode enable signal 46 may include an enable state and a disable state. When the low power mode amplifier 12 is in the enable state, the controller 18 may assert the enable state of the low power mode enable signal 46. Otherwise, the controller 18 may assert the disable state, which turns off the low power mode output stage 42.
The medium power mode amplifier 14 may include a medium power mode switch 48, a medium power mode input matching circuit 50, and a medium power mode output stage 52. The medium power mode switch 48 may be coupled to the output of the secondary input matching circuit 21. The medium power mode switch 48 may have an open state and a closed state. The medium power mode switch 48 may include a medium power mode switch enable signal 54, which permits the controller 18 to change the operating state of the medium power mode switch 48. The controller 18 may close the medium power mode switch 48 when the medium power mode amplifier 14 is enabled. Otherwise, the controller 18 may be configured to open the medium power mode switch 48 when either the low power mode amplifier 12 or the high power mode amplifier 16 is enabled.
The output of the medium power mode switch 48 may be coupled to the input of the medium power mode input matching circuit 50, which provides an output to the medium power mode output stage 52. The medium power mode output stage 52 may form the output of the medium power mode amplifier 14.
The medium power mode output stage 52 may be a linear power amplifier configured to provide a power gain to a received radio frequency input. The medium power mode output stage 52 may include an input to receive a medium power mode enable signal 56 coupled to the controller 18. The medium power mode enable signal 56 may include an enable state and a disable state. To place the medium power mode amplifier 14 in the enable state, the controller 18 may assert the enable state of the medium power mode enable signal 56. Otherwise, the controller 18 may assert the disable state, which turns off the medium power mode output stage 52.
The high power mode amplifier 16 may include a high power mode switch 57, a high power mode input matching circuit 58, a high power mode driver stage 60, a high power mode interstage matching circuit 62, and a high power mode output stage 64. The high power mode switch 57 may be coupled to the input of the high power mode amplifier 16. The high power mode switch 57 may have an open state and a closed state. The high power mode switch 57 may include a high power mode switch enable signal 66, which permits the controller 18 to change the operating state of the high power mode switch 57. The controller 18 may close the high power mode switch 57 when the high power mode amplifier 16 is enabled. Otherwise, the controller 18 may be configured to open the high power mode switch 57 when either the low power mode amplifier 12 or the medium power mode amplifier 14 is enabled.
The output of the high power mode switch 57 may be coupled to the input of the high power mode input matching circuit 58, which provides an output to the high power mode driver stage 60. The high power mode driver stage 60 may be a linear power amplifier configured to provide a power gain to a received radio frequency input. The high power mode driver stage 60 may include an input to receive a high power mode enable signal 61 coupled to the controller 18.
The high power mode enable signal 61 may include an enable state and a disable state. To place the high power mode amplifier 16 in the enable state, the controller 18 may assert the enable state of the high power mode enable signal 61. Otherwise, the controller 18 may assert the disable state, which turns off the high power mode driver stage 60. The output of the high power mode driver stage 60 may be coupled to the high power mode interstage matching circuit 62. The output of the high power mode interstage matching circuit 62 may be coupled to the high power mode output stage 64, which may form the output of the high power mode amplifier 16.
The high power mode output stage 64 may be a linear power amplifier configured to provide high power gain to a received radio frequency input. The high power mode output stage 64 may include a high power mode enable signal 61 coupled to the controller 18. The high power mode enable signal 61 may include an enable state and a disable state. When the high power mode amplifier 16 is in the enable state, the controller 18 may assert the enable state of the high power mode enable signal 61, which turns on the high power mode output stage 64. Otherwise, the controller 18 may assert the disable state, which turns off the high power mode output stage 64. When the high power mode output stage 64 is turned off, or disabled, the high power mode output stage 64 may present a high impedance to the high power mode output matching network 17.
FIG. 2 depicts an operation 100 for controlling the radio frequency power amplifier 10 with continuing reference to FIG. 1. Upon receipt of a command to control the radio frequency power amplifier 10, (Act 102), the controller 18 determines whether to enable the low power mode amplifier 12, the medium power mode amplifier 14, or the high power mode amplifier 16, (Act 104).
In response to a command to enable the high power mode amplifier 16, the controller 18 disables the low power mode output stage 42 and medium power mode output stage 52, (Act 106.) Thereafter, the controller 18 opens the output switch 24 to disconnect the low power mode output stage 42 and medium power mode output stage 52 from the radio frequency output 26, (Act 108.) If present, the controller 18 closes the high power mode switch 57, (Act 109). If present, the controller 18 also opens the low power mode switch 38, the medium power mode switch 48, and load impedance switch 34, (Act 110.) Thereafter, the controller 18 enables the high power mode driver stage 60 and the high power mode output stage 64, (Act 112.)
In response to a command to enable the medium power mode amplifier 14, the controller 18 disables the low power mode output stage 42, the high power mode driver stage 60, and the high power mode output stage 64, (Act 114.) Thereafter, the controller 18 closes the output switch 24 to connect the medium power mode output stage 52 to the radio frequency output 26, (Act 116.) If present, the controller 18 closes the medium power mode switch 48, (Act 118.) If present, the controller 18 also opens the high power mode switch 57 and the low power mode switch 38, (Act 120.) If present, the controller closes the load impedance switch 34, (Act 122.) Thereafter, the controller 18 enables the medium power mode output stage 52, (Act 124.)
In response to a command to enable the low power mode amplifier 12, the controller 18 disables the medium power mode output stage 52, the high power mode driver stage 60, and the high power mode output stage 64, (Act 126.) Thereafter, the controller 18 closes the output switch 24 to connect the low power mode output stage 42 to the radio frequency output 26, (Act 128.) If present, the controller 18 also closes the low power mode switch 38, (Act 130.) If present, the controller 18 opens the medium power mode switch 48 and the high power mode switch 57, (Act 132). If present, the controller closes the load impedance switch 34, (Act 134.) Thereafter, the controller 18 enables the low power mode output stage 42, (Act 136.)
Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

## Claims

1. A power amplifier device comprising:
a power amplifier operable to be enabled and disabled;
an output matching network coupled between the power amplifier and a radio frequency output node such that the power amplifier presents an output impedance to the output matching network and the radio frequency output node presents a load impedance to the output matching network, the output matching network being configured to be switched between transforming the output impedance to a first impedance and transforming the output impedance to a second impedance, wherein the first impedance substantially matches the load impedance and the second impedance is higher than the load impedance;
a controller configured to enable the power amplifier and to switch the output matching network into transforming the output impedance to the first impedance in response to a command to enable the power amplifier.

2. The power amplifier device of claim 1 wherein the controller is further configured to disable the power amplifier and to switch the output matching network into transforming the output impedance to the second impedance in response to a second command.

3. The power amplifier device of claim 2 wherein:
the output matching network comprises:
an output matching circuit configured to transform the output impedance to the first impedance;
a circuit branch having a switch, wherein the circuit branch is configured to present an impedance when the switch is closed such that a combination of the output matching circuit and the circuit branch transform the output impedance to the second impedance, and configured to not present the impedance of the circuit branch when the switch is open so that the output matching circuit transforms the output impedance to the first impedance;

the controller being configured to switch the output matching network into transforming the output impedance to the first impedance by opening the switch in response to the command to enable the power amplifier and being configured to switch the output matching network into transforming the output impedance to the second impedance by closing the switch in response to the second command.

4. The power amplifier device of claim 3 wherein the circuit branch is coupled in shunt between the output matching circuit and the power amplifier.

5. The power amplifier device of claim 1 wherein the power amplifier comprises:
a driver amplifier stage having an output; and
an output amplifier stage having an output, wherein the output of the driver amplifier stage is coupled to the output amplifier stage and the output of the output amplifier stage is coupled to present the output impedance to the output matching network.

6. The power amplifier device of claim 1 wherein the second impedance is substantially higher than the load impedance.

7. The power amplifier device of claim 1 wherein the output matching network is further configured to transform the load impedance into a third impedance presented by the output matching network to the power amplifier when the output matching network is switched into transforming the output impedance to the first impedance, the third impedance substantially matching the output impedance of the power amplifier.

8. The power amplifier device of claim 1 further comprising:
the power amplifier being a high power mode amplifier;
a low power mode amplifier operable to be enabled and disabled, wherein the low power mode amplifier is operably associated with the radio frequency output node;
wherein the controller is further configured to disable the high power mode amplifier and switch the output matching network into transforming the output impedance of the high power mode amplifier to the second impedance in response to a second command to enable the low power mode amplifier.

9. The power amplifier device of claim 8 wherein the controller is further configured to enable the low power mode amplifier in response to the second command to enable the low power mode amplifier.

10. The power amplifier device of claim 9 further comprising a medium power mode amplifier operable to be enabled and disabled and operably associated with the radio frequency output node, wherein the controller is further configured to disable the high power mode amplifier and switch the output matching network into transforming the output impedance of the high power mode amplifier to the second impedance in response to a third command to enable the medium power mode amplifier.

11. The power amplifier device of claim 10 wherein the second impedance is substantially higher than the load impedance such that the high power mode amplifier does not significantly load the low power mode amplifier when the low power mode amplifier is enabled, and does not significantly load the medium power mode amplifier when the medium power mode amplifier is enabled.

12. The power amplifier device of claim 10 wherein the controller is further configured to:
enable the low power mode amplifier and disable the medium power mode amplifier in response to the second command to enable the low power mode amplifier;
enable the medium power mode amplifier and disable the low power mode amplifier in response to the third command to enable the medium power mode amplifier;
disable the low power mode amplifier in response to the command to enable the high power mode amplifier;
disable the low power mode amplifier in response to the third command to enable the medium power mode amplifier;
disable the medium power mode amplifier in response to the command to enable the high power mode amplifier; and
disable the medium power mode amplifier in response to the second command to enable the low power mode amplifier.

13. The power amplifier device of claim 10 further comprising an output switch coupled between the low power mode amplifier and the radio frequency output node, and between the medium power mode amplifier and the radio frequency output node, the controller being further configured to open the output switch in response to the command.

14. The power amplifier device of claim 13 wherein the controller is further configured to:
close the output switch in response to the second command; and
close the output switch in response to the third command.

15. The power amplifier device of claim 14 wherein:
the low power mode amplifier includes a series-coupled low power mode switch;
the medium power mode amplifier include a series-coupled medium power mode switch;
wherein the controller is further configured to:
close the series-coupled low power mode switch in response to the second command;
open the series-coupled medium power mode switch in response to the second command;
close the series-coupled medium power mode switch in response to the third command;
open the series-coupled low power mode switch in response to the third command;
open the series-coupled low power mode switch in response to the command; and
open the series-coupled medium power mode switch in response to the command.

16. A method of operating a power amplifier device, comprising:
enabling a power amplifier in the power amplifier device, wherein the power amplifier presents an output impedance;
transforming the output impedance of the power amplifier to a first impedance while the power amplifier is enabled, wherein the first impedance substantially matches a load impedance presented at a radio frequency output node;
disabling the power amplifier in the power amplifier device; and
transforming the output impedance of the power amplifier to a second impedance while the power amplifier is disabled, wherein the second impedance is higher than the load impedance presented at the radio frequency output node.

17. The method of claim 16 wherein the second impedance is substantially higher than the load impedance.

18. The method of claim 16 wherein enabling the power amplifier in the power amplifier device comprises:
enabling a driver amplifier stage of the power amplifier; and
enabling an output amplifier stage of the power amplifier, wherein the output amplifier stage presents the output impedance.

19. The method of claim 18 wherein disabling the power amplifier in the power amplifier device comprises:
enabling the driver amplifier stage of the power amplifier; and
enabling the output amplifier stage of the power amplifier.

20. The method of claim 16 wherein enabling the power amplifier in the power amplifier device comprises disabling another power amplifier in the power amplifier device.