System and method for RF amplifiers
A digital predistorter comprising a first predistorter for generating out-of-band and inter-band distortion components for compensating for the static nonlinearity of a nonlinear element, and a second predistorter cascaded with the first predistorter, the second predistorter compensating for the in-band distortion of the nonlinear device wherein the cascade of the first predistorter and the second predistorter compensate for in-band, out-of-band and inter-band distortions when the cascade of the first, the second predistorter and the nonlinear element are driven with multiband signals.
1. A digital predistorter comprising:
a first predistorter coupled to receive multiple input signals, and for generating multiple output signals, the first predistorter being configured to compensate for in-band distortion signals around each one of the multiple input signal frequencies;
a frequency distribution network for positioning the multiple output signals from the first predistorter into representative carrier frequencies to generate a multi-band signal; and
a second predistorter coupled to receive the multi-band signal and output a predistorted multi-band signal, the second predistorter generating out-of-band and inter-band distortion remote to frequency bands of the multiple input signals,
wherein the cascade of the first predistorter, the frequency distribution network, and the second predistorter compensate for in-band, out-of-band and inter-band distortions.
2. The digital predistorter of claim 1 , wherein
the first predistorter being characterized by use of the multiple input signals and
the second predistorter being characterized by use of a narrowband signal.
3. The digital predistorter of claim 2 , the second predistorter being a static predistorter.
4. The digital predistorter of claim 2 including a feed back loop, the feedback loop being used for said characterizing of said first predistorter and said second second predistorter.
5. The digital predistorter of claim 4 wherein the feedback loop is a low speed feedback loop.
6. The digital predistorter of claim 2 wherein the cascade of the first predistorter, the frequency distribution network, and the second predistorter further compensate for memory effects.
7. The digital predistorter of claim 1 , wherein the first predistorter compensates for a first nonlinearity in a nonlinear element and the second predistorter compensates for a second nonlinearity in the nonlinear element, and wherein the nonlinear element is one of a single-band amplifier, multiband amplifier, and wideband power amplifier.
8. The digital predistorter of claim 1 , wherein the first predistorter compensates for a first nonlinearity in a nonlinear element and the second predistorter compensates for a second nonlinearity in the nonlinear element, and wherein the nonlinear element is one of a single-branch amplifier, multi-branch amplifier, and phased array transmitter.
9. The digital predistorter of claim 1 , wherein the first predistorter compensates for a first nonlinearity in a nonlinear element and the second predistorter compensates for a second nonlinearity in the nonlinear element, and wherein the nonlinear element is one of a single-input single-output transmitter, and a multi-input multi-output transmitter.
10. A method for suppressing intermodulation distortion produced by nonlinear elements in a transmission signal path comprising:
generating a first predistorted multiple output signal from multiple input signals, the predistorted multiple output signal having in-band distortion around each one of the multiple input signals;
positioning the predistorted multiple output signals into their representative carrier frequencies to generate a multi-band signal; and
generating a second predistorted multi-band signal from the multi-band signal, the second predistorted multi-band signal including out-of-band and inter-band distortions remote to frequency bands of the multiple input signals.
11. The method of claim 10 wherein the nonlinear element is one of a single-band amplifier, multiband amplifier, and wideband power amplifier.
12. The method of claim 10 wherein the nonlinear element is one of a single-branch amplifier, multi-branch amplifier, and phased array transmitter.
13. The method of claim 10 wherein the nonlinear element is one of a single-input single-output transmitter, and a multi-input multi-output transmitter.