Analog power amplifier predistortion methods and apparatus
An embodiment of the invention is a predistortion approach to linearize a power amplifier by using one or more analog multiplier(s) and a DSP-based processor. For the analog embodiment, the inherent nature of the analog circuitries allows digital predistortion processing structured directly at the RF band, and enables a single power amplifier to support multi-modulation schemes, multi-carriers and multi-channels. As a result, the predistortion architecture is particularly suitable for wireless transmission systems, such as base-stations, repeaters, and indoor signal coverage systems. The wireless system performance can be improved and upgraded just by using the new PA module rather than change or rebuild new subsystem in existing base station. The analog embodiment can also mix and match its analog multipliers with other analog components such as phase splitters, phase shifters, attenuators, filters, couplers, mixers, low-noise amplifiers, buffers, envelope detectors, and etc., to provide additional features.
1. A predistortion architecture for linearizing an output of a power amplifier for wireless transmission systems, the predistortion architecture comprising:
an RF input adapted to receive multi-channel RF input signals using multiple modulation schemes;
a first down converter coupled to the RF input and configured to produce a first analog signal representative of the RF input signals;
a first analog-to-digital converter for converting the first analog signal into a first digital signal;
a DSP-based processor logic for generating at least one digital correction signal derived from the RF input signals;
at least one digital-to-analog converter for converting the at least one digital correction signal into at least one analog correction signal;
an analog multiplier for combining, in an RF band, the RF input signals and the at least one analog correction signal to form a predistorted signal; and
an output for providing to a power amplifier the predistorted signal configured to substantially linearize the output of the power amplifier;
a second down converter coupled to the output of the power amplifier, the second down converter configured to produce a second analog signal representative of the output of the power amplifier; and
a second analog-to-digital converter for converting the second analog signal into a second digital signal, wherein the DSP-based processor logic comprises:
an error logic configured to determine an error between the first digital signal and the second digital signal;
an address former configured to generate a lookup-table key based on the first digital signal; and
at least one lookup table configured to generate the at least one digital correction signal based on the lookup-table key and the error between the first digital signal and the second digital signal.
2. The predistortion architecture of claim 1 wherein the wireless transmission systems comprise a base-station.
3. The predistortion architecture of claim 1 wherein the wireless transmission systems comprise a repeater.
4. The predistortion architecture of claim 1 wherein the wireless transmission systems comprise an indoor signal coverage system.
5. A predistortion architecture for linearizing an output of a power amplifier for wireless transmission systems, the predistortion architecture comprising:
an RF input adapted to receive multi-channel RF input signals using multiple modulation schemes;
a first down converter coupled to the RF input;
a DSP-based processor logic for generating at least one digital correction signal derived from the RF input signals;
at least one digital-to-analog converter for converting the at least one digital correction signal into at least one analog correction signal;
an analog multiplier for combining, in an RF band, the RF input signals and the at least one analog correction signal to form a predistorted signal; and
an output for providing to a power amplifier the predistorted signal configured to substantially linearize the output of the power amplifier,
wherein the analog multiplier comprises:
a phase splitter configured to split the RF input signals into a plurality of phase-split input signals;
a plurality of amplitude adjusters; and
an adder;
wherein:
the at least one digital correction signal comprises a plurality of digital correction signals;
the at least one analog correction signal comprises a plurality of analog correction signals;
the at least one digital-to-analog converter comprises a plurality of digital-to-analog converters, each digital-to-analog converter configured to convert a respective digital correction signal into a corresponding analog correction signal;
each amplitude adjuster is configured to combine a respective phase-split input signal and a respective analog correction signal to form a respective predistorted phase-split signal; and
the adder is configured to combine the plurality of predistorted phase-split signals to form the predistorted signal.
6. The predistortion architecture of claim 5 wherein the wireless transmission systems comprise a base-station.
7. The predistortion architecture of claim 5 wherein the wireless transmission systems comprise a repeater.
8. The predistortion architecture of claim 5 wherein the wireless transmission systems comprise an indoor signal coverage system.
9. A predistortion architecture for linearizing an output of a power amplifier for wireless transmission systems, the predistortion architecture comprising:
an RF input adapted to receive multi-channel RF input signals using multiple modulation schemes;
a first down converter coupled to the RF input;
a DSP-based processor logic for generating at least one digital correction signal derived from the RF input signals;
at least one digital-to-analog converter for converting the at least one digital correction signal into at least one analog correction signal;
an analog multiplier for combining, in an RF band, the RF input signals and the at least one analog correction signal to form a predistorted signal; and
an output for providing to a power amplifier the predistorted signal configured to substantially linearize the output of the power amplifier,
wherein the analog multiplier comprises:
a phase shifter coupled to the RF input; and
an amplitude adjuster coupled to the phase shifter;
wherein:
the at least one digital correction signal comprises a digital phase correction signal and a digital amplitude correction signal;
the at least one analog correction signal comprises an analog phase correction signal and an analog amplitude correction signal;
the at least one digital-to-analog converter comprises a first digital-to-analog converter and a second digital-to-analog converter, the first digital-to-analog converter configured to convert the digital phase correction signal into the analog phase correction signal, the second digital-to-analog converter configured to convert the digital amplitude correction signal into the analog amplitude correction signal;
the phase shifter is configured to combine the RF input signals and the analog phase correction signal to form a phase-shifted signal; and
the amplitude adjuster is configured to combine the phase-shifted signal and the analog amplitude correction signal to form the predistorted signal.
10. The predistortion architecture of claim 9 wherein the wireless transmission systems comprise a base-station.
11. The predistortion architecture of claim 9 wherein the wireless transmission systems comprise a repeater.
12. The predistortion architecture of claim 9 wherein the wireless transmission systems comprise an indoor signal coverage system.