Linearizing LINC amplifiers using pre-distortion
View Patent ↗An input signal having amplitude information is pre-distorted and converted into two pre-distorted signals without amplitude information. The two pre-distorted signals are separately amplified and then recombined to generate a linearized amplified output signal having amplitude information. The pre-distortion and conversion may be implemented using a pre-distorter and a LINC modulator. Alternatively, the pre-distortion and conversion may be implemented in circuitry that combines the functions of a pre-distorter and a LINC modulator. The amplified, pre-distorted signals are preferably combined using circuitry that provides at least some impedance matching, such as a transformer or a transmission line tee with transmission line stubs.
1. A method for generating a linearized amplified output signal from an input signal having amplitude information, the method comprising:
converting the input signal into two pre-distorted signals having the amplitude information converted into phase modulation;
separately amplifying the two pre-distorted signals; and
combining the two amplified, pre-distorted signals to generate the linearized amplified output signal.
2. The invention of claim 1 , wherein:
the input signal is an RF signal; and
the linearized amplified output signal is an RF signal having amplitude information.
3. The invention of claim 1 , wherein converting the input signal comprises:
pre-distorting the input signal to generate a pre-distorted input signal having a pre-distorted amplitude; and
converting the pre-distorted input signal into the two pre-distorted signals having the pre-distorted amplitude converted into phase modulation.
4. The invention of claim 3 , wherein pre-distorting the input signal comprises pre-distorting both amplitude and phase of the input signal.
5. The invention of claim 1 , wherein converting the input signal comprises:
generating a phase pre-distortion term from the input signal;
generating an amplitude pre-distortion term from the input signal;
detecting phase of the input signal;
combining the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a first manner and modulating at a carrier frequency to generate a first pre-distorted signal having the amplitude information converted into phase modulation; and
combining the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a second manner and modulating at the carrier frequency to generate a second pre-distorted signal having the amplitude information converted into phase modulation.
6. The invention of claim 5 , wherein generating the phase and amplitude pre-distortion terms comprise:
detecting amplitude of the input signal;
retrieving the phase pre-distortion term from a first look-up table based on the detected amplitude; and
retrieving the amplitude pre-distortion term from a second look-up table based on the detected amplitude.
7. The invention of claim 5 , wherein:
in the first manner, the amplitude pre-distortion term is subtracted from the sum of the phase pre-distortion term and the phase; and
in the second manner, the amplitude pre-distortion term is added to the sum of the phase pre-distortion term and the phase.
8. The invention of claim 1 , wherein combining the two amplified, pre-distorted signals is implemented using a transformer.
9. The invention of claim 1 , wherein combining the two amplified, pre-distorted signals is implemented using a transmission line tee with transmission stubs for impedance matching.
10. The invention of claim 9 , wherein the transmission stubs comprise shunt reactances placed an electrical equivalent of one-quarter wavelength away from the transmission line tee.
11. An amplifier circuit adapted to generate a linearized amplified output signal from an input signal having amplitude information, the amplifier circuit comprising:
means for converting the input signal into two pre-distorted signals having the amplitude information converted into phase modulation;
means for separately amplifying the two pre-distorted signals; and
means for combining the two amplified, pre-distorted signals to generate the linearized amplified output signal.
12. An amplifier circuit adapted to generate a linearized amplified output signal from an input signal having amplitude information, the amplifier circuit comprising:
circuitry adapted to convert the input signal into two pre-distorted signals having the amplitude information converted into phase modulation;
two amplifiers adapted to separately amplify the two pre-distorted signals; and
a combiner adapted to combine the two amplified, pre-distorted signals to generate the linearized amplified output signal.
13. The invention of claim 12 , wherein:
the input signal is an RF signal; and
the linearized amplified output signal is an RF signal having amplitude information.
14. The invention of claim 12 , wherein the circuitry adapted to convert the input signal comprises:
a pre-distorter adapted to pre-distort the input signal to generate a pre-distorted input signal having a pre-distorted amplitude; and
a LINC modulator adapted to convert the pre-distorted input signal into the two pre-distored signals having the pre-distorted amplitude converted into phase modulation.
15. The invention of claim 14 , wherein the pre-distorter is adapted to pre-distort both amplitude and phase of the input signal.
16. The invention of claim 12 , wherein the circuitry adapted to convert the input signal comprises:
circuitry adapted to generate a phase pre-distortion term from the input signal;
circuitry adapted to generate an amplitude pre-distortion term from the input signal;
a phase detector adapted to detect phase of the input signal;
circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a first manner and modulating at a carrier frequency to generate a first pre-distorted signal having the amplitude information converted into phase modulation; and
circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a second manner and modulating at the carrier frequency to generate a second pre-distorted signal having the amplitude information converted into phase modulation.
17. The invention of claim 16 , wherein the circuitry adapted to generate the phase and amplitude pre-distortion terms comprises:
an envelope detector adapted to detect amplitude of the input signal;
a first look-up table adapted to provide the phase pre-distortion term based on the detected amplitude; and
a second look-up table adapted to provide the amplitude pre-distortion term based on the detected amplitude.
18. The invention of claim 16 , wherein:
the circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in the first manner is adapted to generate a signal corresponding to the amplitude pre-distortion term subtracted from the sum of the phase pre-distortion term and the phase; and
the circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in the second manner is adapted to generate a signal corresponding to the amplitude pre-distortion term added to the sum of the phase pre-distortion term and the phase.
19. The invention of claim 18 , wherein the circuitry adapted to generate the first and second pre-distorted signals comprises:
a subtraction node adapted to subtract the amplitude pre-distortion term from the phase pre-distortion term;
a first addition node adapted to add the amplitude pre-distortion term to the phase pre-distortion term;
a second addition node adapted to add the phase to the output from the subtraction node;
a first modulator adapted to modulate the output from the second addition node at the carrier frequency to generate the first pre-distorted signal;
a third addition node adapted to add the phase to the output from the first addition node; and
a second modulator adapted to modulate the output from the third addition node at the carrier frequency to generate the second pre-distorted signal.
20. The invention of claim 12 , wherein the combiner comprises a transformer.
21. The invention of claim 12 , wherein combiner comprises a transmission line tee with transmission stubs for impedance matching.
22. The invention of claim 21 , wherein the transmission stubs comprise shunt reactances placed an electrical equivalent of one-quarter wavelength away from the transmission line tee.