Linearization in the presence of phase variations
View Patent ↗In one embodiment, a non-linear power amplifier generates an amplified output signal based on a pre-distorted signal generated by a digital pre-distorter based on an input signal. A feedback path generates a feedback waveform based on the amplified output signal. The feedback waveform is aligned in time with the input signal at the waveform level to identify a corresponding reference waveform. The feedback waveform and the corresponding reference waveform are both divided into a plurality of sub-waveforms. Each feedback sub-waveform is independently aligned in phase with its corresponding reference sub-waveform. The resulting plurality of phase-aligned feedback sub-waveforms are then combined to form a hybrid-aligned waveform that is compared to the reference waveform to adaptively update the digital pre-distorter.
1. A machine-implemented method for generating a linearized output signal from an input signal, the method comprising:
(1) applying the input signal to an adaptive pre-distorter to generate a pre-distorted signal;
(2) applying the pre-distorted signal to a non-linear amplifier to generate the linearized output signal;
(3) generating a feedback signal based on the linearized output signal; and
(4) adapting the adaptive pre-distorter based on the input signal and the feedback signal by:
(a) time aligning, at a waveform level, a feedback waveform corresponding to the feedback signal with a reference waveform corresponding to the input signal;
(b) dividing the time-aligned feedback waveform in time into a plurality of feedback sub-waveforms, wherein each feedback sub-waveform has a shorter time interval than the feedback waveform;
(c) dividing the reference waveform in time into a plurality of reference sub-waveforms, wherein each reference sub-waveform has a shorter time interval than the reference waveform and each reference sub-waveform corresponds to a different feedback sub-waveform;
(d) independently phase-aligning each feedback sub-waveform to its corresponding reference sub-waveform at a sub-waveform level to form a plurality of independently phase-aligned feedback sub-waveforms;
(e) combining the plurality of independently phase-aligned feedback sub-waveforms in time to form a hybrid-aligned feedback waveform; and
(f) updating the adaptive pre-distorter based on the hybrid-aligned feedback waveform.
2. The invention of claim 1 , wherein step (f) comprises comparing the hybrid-aligned feedback waveform to the reference waveform to characterize differences between the hybrid-aligned feedback and reference waveforms.
3. The invention of claim 1 , wherein:
the adaptive pre-distorter is a digital pre-distorter; and
the non-linear amplifier comprises a power amplifier.
4. The invention of claim 1 , wherein each phase-aligning corresponds to rotation of a complex signal vector in a complex signal domain.
5. Apparatus comprising a linearized system comprising:
an adaptive pre-distorter configured to pre-distort an input signal to generate a pre-distorted signal;
a non-linear amplifier configured to generate a linearized output signal from the pre-distorted signal; and
a feedback path configured to generate a feedback waveform based on the linearized output signal, wherein the adaptive pre-distorter is configured to:
(1) time align the feedback waveform with a corresponding reference waveform of the input signal at a waveform level;
(2) divide the time-aligned feedback waveform in time into a plurality of feedback sub-waveforms, wherein each feedback sub-waveform has a shorter time interval than the feedback waveform;
(3) divide the corresponding reference waveform in time into a plurality of reference sub-waveforms, wherein each reference sub-waveform has a shorter time interval than the reference waveform;
(4) independently phase align each feedback sub-waveform and its corresponding reference sub-waveform at a sub-waveform level to form a plurality of phase-aligned sub-waveforms;
(5) combine the plurality of phase-aligned sub-waveforms in time to form a hybrid-aligned waveform; and
(6) update the adaptive pre-distorter based on the hybrid-aligned waveform.
6. The invention of claim 5 , wherein:
the hybrid-aligned waveform is a hybrid-aligned feedback waveform; and
the adaptive pre-distorter is updated based on a comparison of the hybrid-aligned feedback waveform and the corresponding reference waveform.
7. The invention of claim 5 , wherein:
the hybrid-aligned waveform is a hybrid-aligned reference waveform; and
the adaptive pre-distorter is updated based on a comparison of the hybrid-aligned reference waveform and the corresponding feedback waveform.
8. The invention of claim 5 , wherein:
the adaptive pre-distorter is an adaptive digital pre-distorter; and
the non-linear amplifier comprises a power amplifier.
9. The invention of claim 5 , wherein each phase-aligning corresponds to rotation of a complex signal vector in a complex signal domain.