Apparatus and method of power management using envelope-stacking

1. A reduced current RF power amplifier system comprising:

a first RF amplifier for amplifying a first RF input signal and generating a first RF output signal;

a second RF amplifier for amplifying a second RF input signal and generating a second RF output signal;

a stack/unstack controller including circuitry configured to switch the RF power amplifier system between a stacked mode in which said first and second RF amplifiers are coupled in a stacked configuration and an unstacked mode in which said first and second RF amplifiers are coupled in an unstacked configuration in response to one or more mode-control signals, the stacked configuration providing reduced current compared to the unstacked configuration; and

a linearity detector configured to detect if both of said first and second RF amplifiers would operate linearly in the stacked configuration and to generate the one or more mode-control signals to specify the stacked mode when the linearity detector detects that both of said first and second RF amplifiers would operate linearly in the stacked configuration and to specify the unstacked mode when the linearity detector detects that either of said first and second RF amplifiers would operate nonlinearly in the stacked configuration.

2. The system according to claim 1 , wherein:

a majority of DC current of said first and second RF amplifiers is shared when in said stacked configuration; and

a majority of DC current of said first and second RF amplifiers is not shared when in said unstacked configuration.

3. The system according to claim 1 , wherein the stack/unstack controller is configured to switch the first and second RF amplifiers between the stacked and unstacked configurations in a manner that maintains linearity in the first and second RF amplifiers.

4. The system according to claim 1 , wherein:

the first RF amplifier is coupled to a first negative power supply and is coupled through one or more first stack-control signals to the stack/unstack controller;

the second RF amplifier is coupled to a first positive power supply and is coupled through one or more second stack-control signals to the stack/unstack controller; and

the stack/unstack controller is coupled to a second positive power supply and to a second negative power supply, wherein:

the stack/unstack controller operates on said first and second stack-control signals to couple the first and second RF amplifiers in the stacked configuration between the first positive and first negative power supplies when the one or more mode-control signals indicate the stacked mode; and

the stack/unstack controller operates on said first and second stack-control signals from the first and second RF amplifiers to couple the first and second RF amplifiers in the unstacked configuration between the second positive and second negative power supplies when the one or more mode-control signals indicate the unstacked mode.

5. The system according to claim 4 , wherein said stack/unstack controller comprises switches to move said first and second stack-control signals toward said second positive and second negative power supplies when said one or more mode-control inputs identify the unstacked mode.

6. The system according to claim 4 , wherein said second negative power supply is the same as said first negative power supply and said second positive power supply is the same as said first positive power supply.

7. The system according to claim 1 , wherein said first RF amplifier comprises a NMOS amplifier and wherein said second RF amplifier comprises a PMOS amplifier.

8. The system according to claim 1 , wherein each of said one or more mode-control inputs is a dynamic signal that varies in response to the modulation envelope of at least one of said first or second RF input signals.

9. The system according to claim 1 , further comprising:

one or more RF connections between said first and second RF amplifiers, wherein said one or more RF connections provide a path for DC current to flow when in the stacked configuration.

10. The system according to claim 1 , wherein:

said second negative power supply is a virtual ground node within said first RF amplifier; and

said second positive power supply is a virtual ground node within said second RF amplifier.

11. The system according to claim 1 , further comprising:

a power combiner operable to combine the powers in said first and second RF output signals into a single RF signal.

12. The system according to claim 10 , wherein said linearity detector comprises one or more peak detectors operable to generate an envelope signal representative of the envelope of one or more of said first and second RF output signals.

13. The system according to claim 1 , further comprising:

a power tracker configured to monitor a baseband system power code, wherein the one or more mode-control signals are generated as a function of such baseband system power code monitoring.

14. The system according to claim 1 , wherein said stack/unstack controller comprises FETs to provide additional current to said first and second RF amplifiers when said one or more mode-control inputs specify an unstacked configuration.

15. The system according to claim 1 , wherein said stack/unstack controller comprises a switch or diode to provide a DC current path between said first and second RF amplifiers when said one or more mode-control inputs specify a stacked configuration.

16. The system according to claim 1 , further comprising bias circuitry to control the DC voltage of said first and second RF outputs when said first and second amplifiers are in a stacked configuration.

17. A method of reducing the current of an RF power amplifier system having first and second RF amplifiers and a stack/unstack controller including circuitry configured to switch the RF power amplifier system between a stacked mode in which said first and second RF amplifiers are coupled in a stacked configuration and an unstacked mode in which said first and second RF amplifiers are coupled in an unstacked configuration in response to one or more mode-control signals, the stacked configuration providing reduced current compared to the unstacked configuration, the method comprising:

detecting, by a linearity detector, if both of said first and second RF amplifiers would operate linearly in the stacked configuration;

generating, by the linearity detector, the one or more mode-control signals to specify the stacked mode when the linearity detector detects that both of said first and second RF amplifiers would operate linearly in the stacked configuration;

generating, by the linearity detector, the one of more mode-control signals to specify the unstacked mode when the linearity detector detects that either of said first and second RF amplifiers would operate nonlinearly in the stacked configuration;

receiving, by the stack/unstack controller, the one or more mode-control signals from the linearity detector; and

switching, by the stack/unstack controller, the first and second RF amplifiers into the mode indicated by the mode-control signal.

18. The method according to claim 17 , further comprising:

combining, using a power combiner, the powers in said first and second RF output signals into a single RF signal.

19. The method according to claim 17 , further comprising:

monitoring a baseband system power code; and

generating the one or more mode-control signals as a function of such baseband system power code monitoring.

20. The method according to claim 17 , wherein each of said one or more mode-control inputs is a dynamic signal that varies in response to the modulation envelope of at least one of said first or second RF input signals.