Efficient, precise RF modulation using multiple amplifier stages

• US 20020079962A1
• Filed: 12/21/2000
• Published: 06/27/2002
• Est. Priority Date: 12/21/2000
• Status: Active Grant

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Tropian, Inc. (Panasonic Holdings Corporation)
• Inventors: Sander, Wendell B.
• Granted Patent: US 6,690,233 B2
• Time in Patent Office: Days
• US Class Current: 330/124R
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence
• CPC Class Codes: H03F 1/0222 by using a signal derived from the input signal
• CPC Class Codes: H03F 1/0294 using vector summing of two or more constant amplitude phase-modulated signals

Abstract

The present invention, generally speaking, provides a highly efficient RF power amplifier having a large output dynamic range. The amplifier avoid the large power dissipation that occurs in the LINC combiner at lower output levels. In general, this is achieved by using power-controlled switch-mode power amplifiers to vary output power at large power outputs, and reverting to LINC only at low output powers. Thus the present invention achieves the desirable combination of high efficiency at all output powers, while maintaining the fine output power control of the LINC method. More particularly, the power amplifier is based on a highly efficient structure in which amplitude modulation/power control of the output of an RF amplifier is achieved by operating the amplifier in switch mode and varying the power supply of the amplifier, as described more fully in U.S. patent application Ser. No. 09/637,269 entitled High-Efficiency Modulating RF Amplifier, filed Aug. 10, 2000 and incorporated herein by reference. Such an amplifier behaves quite linearly at high power but may exhibit non-linearity at lower output powers. Good linearity throughout a wide dynamic range, and particularly at low output power, may be achieved by phasing and combining the outputs of two (or more) such amplifiers. At high and medium power, the outputs are combined in-phase, allowing for low-loss, high-efficiency operation. At low power, the outputs are phased such that power subtraction occurs. In this manner, each amplifier may be operated at a power level that exhibits good linearity while producing an output signal of a lower power level that would normally fall within a region of substantial non-linearity.

Claims

1. An RF power amplifier, comprising:

a first amplifier block producing a variable magnitude output signal;

a further amplifier block; and

circuitry for controlling the magnitude of the variable magnitude output signal and for phasing and combining output signals of the amplifier blocks such that, at higher desired output power levels, the output signals combine substantially in-phase, and at lower desired output power levels, the output signals combine less in-phase.

2. The apparatus of claim 1, wherein said first amplifier block comprises:

an amplifier stage operated in switch mode; and

circuitry for varying the power of an output signal of the amplifier stage by varying a supply voltage applied to the amplifier stage.

3. The apparatus of claim 2, wherein said further amplifier block comprises:

an amplifier stage operated in switch mode; and

circuitry for varying the power of an output signal of the amplifier stage by varying a supply voltage applied to the amplifier stage.

4. The apparatus of claim 1, wherein said circuitry for controlling and for phasing and combining comprises:

a magnitude controller responsive to a magnitude input signal for producing magnitude drive signals for the first amplifier block and the further amplifier block;

a phase controller responsive to a phase input signal for producing phase drive signals for the first amplifier block and the further amplifier block; and

a combiner for combining output signals of the first amplifier block and the further amplifier block.

5. The apparatus of claim 4, wherein the magnitude controller varies the magnitude drive signals in proportional relationship to the magnitude input signal during such time as the magnitude drive signals exceed a threshold level.

6. The apparatus of claim 5, wherein the magnitude controller departs from said proportional relationship when adhering to said proportional relationship would cause the magnitude drive signals fall below the threshold level.

7. The apparatus of claim 6, wherein the magnitude controller holds the magnitude drive signals substantially constant at said threshold level when adhering to said proportional relationship would cause the magnitude drive signals fall below the threshold level.

8. The apparatus of claim 4, wherein the phase controller produces multiple substantially identical phase drive signals during such time as the magnitude drive signals exceed a threshold level.

9. The apparatus of claim 8, wherein the phase controller produces multiple substantially different phase drive signals during such time as the magnitude drive signals do not exceed the threshold level.

10. The apparatus of claim 9, wherein the phase controller produces multiple phase drive signals calculated according to phase offsets from a desired output signal phase.

11. The apparatus of claim 10, wherein said phase offsets are calculated in accordance with a trigonometric function having as its argument a ratio of the magnitude input signal and the threshold.

13. The method of claim 12, further comprising:

operating an amplifier stage of the first amplifier block in switch mode; and

varying the magnitude of the variable magnitude output signal varying a supply voltage applied to the amplifier stage of the first amplifier block.

14. The apparatus of claim 2, further comprising:

operating an amplifier stage of the further amplifier block in switch mode; and

varying the magnitude of an output signal of the further amplifier stage by varying a supply voltage applied to the amplifier stage of the further amplifier block.

15. The method of claim 12, wherein the further amplifier block produces a variable magnitude output signal.

16. The method of claim 15, wherein magnitudes of the variable magnitude output signals of the first amplifier block and the further amplifier block are controlled substantially as follows:

If MAG<

MIN, M_A=M_B=MIN

else M_A=M_B=MIN/2;

where MAG is a desired output power level, MIN is a threshold output power level, M_A is the magnitude of the variable magnitude output signal of the first amplifier block, and MB is the magnitude of the variable magnitude output signal of the further amplifier block.

17. The method of claim 16, wherein output signals of the amplifier blocks are phased substantially as follows:

If MAG>

MIN, φ

_A=φ

_B=φ

_i

else φ

_A=φ

_i+cos<sup>−

1</sup>(MAG/MIN), φ

_B=φ

_i−

cos<sup>−

1</sup>(MAG/MIN);

where φ

_i is a desired output signal phase.

18. The method of claim 15, wherein output signals of the amplifier blocks are phased substantially as follows:

If MAG>

MIN, φ

_A=φ

_B=φ

_i

else φ

_A=φ

_i+cos<sup>−

1</sup>(MAG/MIN), φ

_B=φ

_i−

cos<sup>−

1</sup>(MAG/MIN);

where MAG is a desired output power level, MIN is a threshold output power level, and φ

_i is a desired output signal phase.

19. The method of claim 18, wherein magnitudes of the variable magnitude output signals of the first amplifier block and the further amplifier block are controlled substantially as follows:

If MAG<

MIN, M_A=M_B=MIN

else M_A=M_B=MIN/2;

where M_A is the magnitude of the variable magnitude output signal of the first amplifier block, and MB is the magnitude of the variable magnitude output signal of the further amplifier block.

12. A method of operating an RF power amplifier having a plurality of amplifier blocks including a first amplifier block producing a variable magnitude output signal and a further amplifier block, the method comprising:

controlling the magnitude of the variable magnitude output signal;

at higher desired output power levels, phasing and combining output signals of the amplifier blocks such that the output signals combine substantially in-phase; and

at lower desired output power levels, phasing and combining output signals of the amplifier blocks such that the output signals combine less in-phase.