Double-LINC Switched-Mode Transmitter

• US 20090311980A1
• Filed: 06/16/2008
• Published: 12/17/2009
• Est. Priority Date: 06/16/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Sjoland, Henrik
• Granted Patent: US 7,957,712 B2
• Time in Patent Office: Days
• US Class Current: 455/127.300
• CPC Class Codes: H03F 1/0294 using vector summing of two or more constant amplitude phase-modulated signals
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/24 of transmitter output stages

Abstract

Disclosed herein are methods and apparatus for processing an input information signal having varying amplitude and phase to obtain an amplified output signal having the same amplitude and phase variation. In an exemplary method, an input information signal is decomposed into two pairs of constant-envelope component signals such that the vector sum of the first pair is orthogonal to the vector sum of the second pair, for desired signal amplitudes below a level corresponding to a pre-determined threshold. For desired signal amplitudes above this level, the input information signal is instead decomposed into two pairs of constant-envelope component signals such that the vector sum of the first pair is separated by less than ninety degrees from the vector sum of the second pair. The constant-envelope component signals may be amplified by highly-efficient non-linear amplifier elements and combined to obtain the amplified output signal.

Claims

1. A method of processing an input information signal of varying amplitude and phase to obtain an amplified output signal, the method comprising:

for desired output signal amplitudes below a first level corresponding to a first pre-determined threshold, decomposing the input information signal into two pairs of constant-envelope component signals such that the vector sum of the first pair of component signals is orthogonal to the vector sum of the second pair of component signals;

for desired output signal amplitudes above the first level, decomposing the input information signal into two pairs of constant-envelope component signals such that the vector sum of the first pair of component signals is separated by less than ninety degrees from the vector sum of the second pair of component signals;

generating a plurality of amplifier input signals from the constant-envelope component signals;

amplifying each amplifier input signal with a separate amplifier element; and

combining the amplified signals to obtain the output signal.

2. The method of claim 1, wherein the vector sum of the component signals is substantially equal to the input information signal.

3. The method of claim 1, wherein the vector sum of the component signals is proportional to the input information signal and is at a constant phase offset from the input information signal.

4. The method of claim 1, wherein decomposing the input information signal into two pairs of constant-envelope component signals comprises, for a desired output signal amplitude equal to or above a second level corresponding to a second pre-determined threshold, generating the component signals such that the vector sums of each pair of component signals have the same phase.

5. The method of claim 1, wherein the separate amplifier elements have substantially identical gain and phase characteristics.

6. The method of claim 1, wherein decomposing the input information signal into two pairs of constant-envelope component signals for desired output signal amplitudes below the first level comprises:

determining an in-phase component and a quadrature component for the input information signal;

generating the first pair of constant-envelope component signals such that the vector sum of the first pair of component signals is substantially equal to the in-phase component; and

generating the second pair of constant-envelope component signals such that the vector sum of the second pair of component signals is substantially equal to the in-phase component.

7. The method of claim 1, further comprising determining a parameter value, α

, as a function of the desired output signal amplitude, wherein decomposing the input information signal into two pairs of constant-envelope component signals for desired output signal amplitudes above the first level comprises;

generating the first pair of constant-envelope component signals such that the vector sum of the first pair of component signals is proportional to

8. The method of claim 7, wherein determining the parameter value comprises retrieving the parameter value from a look-up table indexed by an index parameter corresponding to the desired output signal amplitude.

9. The method of claim 8, wherein determining the parameter value further comprises interpolating between entries in the look-up table.

10. The method of claim 1, wherein the constant-envelope component signals are at a baseband frequency or an intermediate frequency, and wherein generating a plurality of amplifier input signals from the constant-envelope component signals comprises upconverting each of the constant-envelope component signals to an amplifier input signal at the output signal frequency.

11. The method of claim 1, wherein generating a plurality of amplifier input signals from the constant-envelope component signals comprises generating a pulse-width modulated amplifier input signal from each pair of constant-envelope component signals.

12. A transmitter circuit for processing an input information signal of varying amplitude and phase to obtain an amplified output signal, the transmitter circuit comprising:

a signal processing circuit configured to decompose the input information signal into two pairs of constant-envelope component signals so that the sum of the first pair of component signals is orthogonal to the sum of the second pair of component signals for desired output signal amplitudes below a first level corresponding to a first pre-determined threshold and the sum of the first pair of component signals is separated by less than ninety degrees from the sum of the second pair of component signals for desired output signal amplitudes above the first level;

a generator circuit configured to generate a plurality of amplifier input signals from the constant-envelope component signals;

an amplifier element for each amplifier input signal, each amplifier element configured to amplify a respective one of the amplifier input signals; and

a combining circuit configured to combine the amplified signals to obtain the output signal.

13. The transmitter circuit of claim 12, wherein the vector sum of the component signals is substantially equal to the input information signal.

14. The transmitter circuit of claim 12, wherein the vector sum of the component signals is proportional to the input information signal and is at a constant phase offset from the input information signal.

15. The transmitter circuit of claim 12, wherein the signal processing circuit is configured to decompose the input information signal into two pairs of constant-envelope component signals for a desired output signal amplitude equal to or above a level corresponding to a second pre-determined threshold by generating the component signals such that the vector sums of each pair of component signals have the same phase.

16. The transmitter circuit of claim 12, wherein the amplifier elements have substantially identical gain and phase characteristics.

17. The transmitter circuit of claim 12, wherein the signal processing circuit is configured to decompose the input information signal into two pairs of constant-envelope component signals for desired output signal amplitudes below the first level by:

determining an in-phase component and a quadrature component for the input information signal;

generating the first pair of constant-envelope component signals such that the vector sum of the first pair of component signals is substantially equal to the in-phase component; and

generating the second pair of constant-envelope component signals such that the vector sum of the second pair of component signals is substantially equal to the quadrature component.

18. The transmitter circuit of claim 12, wherein the signal processing circuit is further configured to determine a parameter value, α

, as a function of the desired output signal amplitude, and to decompose the input information signal into two pairs of constant-envelope component signals for desired output signal amplitudes above the first level by;

generating the first pair of constant-envelope component signals such that the vector sum of the first pair of component signals is proportional to

19. The transmitter circuit of claim 18, wherein the signal processing circuit is configured to determine the parameter value by retrieving the parameter value from a look-up table indexed by an index parameter corresponding to the desired output signal amplitude.

20. The transmitter circuit of claim 19, wherein the signal processing circuit is further configured to determine the parameter value by interpolating between entries in the look-up table.

21. The transmitter circuit of claim 12, wherein the signal processing circuit is configured to generate the constant-envelope component signals at a baseband or intermediate frequency, and wherein the generator circuit comprises an upconverter circuit configured to upconvert each of the constant-envelope component signals to an output signal frequency prior to amplification by the amplifier elements.

22. The transmitter circuit of claim 12, wherein the generator circuit comprises a pulse-width modulator circuit configured to generate a pulse-width modulated amplifier input signal from each pair of constant-envelope component signals.