Multi-band wide band power amplifier digital predistortion system
A high performance and cost effective method of RF-digital hybrid mode power amplifier systems with high linearity and high efficiency for multi-frequency band wideband communication system applications is disclosed. The present disclosure enables a power amplifier system to be field reconfigurable and support multiple operating frequency bands on the same PA system over a very wide bandwidth. In addition, the present invention supports multi-modulation schemes (modulation agnostic), multi-carriers and multi-channels.
1. A digital predistortion system comprising:
a digital predistorter configured to receive a digital input signal and to output a predistorted output signal;
aliasing logic configured to alias the predistorted output signal and to output an aliased predistorted output signal;
a power amplifier configured to receive the predistorted output signal and to output an amplified output;
feedback components configured to derive a feedback signal from the amplified output and to sample the feedback signal; and
a digital predistortion estimator configured to compare the aliased predistorted output signal to the sampled feedback signal and to calculate at least one predistortion coefficient based upon the comparison.
2. The digital predistortion system of claim 1 , wherein a sampling rate of the aliased predistorted output signal is less than twice a maximum bandwidth of the feedback signal.
3. The digital predistortion system of claim 1 , wherein the digital input signal is a multi-band input signal.
4. The digital predistortion system of claim 1 , wherein the digital predistorter is configured to effect the at least one predistortion coefficient derived by the digital predistortion estimator.
5. The digital predistortion system of claim 1 , wherein the digital predistorter utilizes an adaptive polynomial-based digital predistortion system, the polynomial-based digital predistortion system utilizing the at least one predistortion coefficient generated by the digital predistortion estimator.
6. The digital predistortion system of claim 1 , wherein the digital predistorter utilizes a look-up-table-based digital predistortion system with finite impulse response filters, wherein coefficients for the finite impulse response filters comprise the at least one predistortion coefficient derived by the digital predistortion estimator.
7. The digital predistortion system of claim 1 , further comprising alignment logic that aligns the feedback signal relative to the digital input signal.
8. The digital predistortion system of claim 1 , wherein the at least one predistortion coefficient is derived to account for memory effects due to one or more of self-heating, bias networks, and frequency dependencies of active devices in the digital predistortion system.
9. A method for amplifying signals, the method comprising:
receiving a first digital input signal;
detecting a predistorted output signal from a digital predistorter, the predistorted output signal being responsive to the first digital input signal;
aliasing the predistorted output signal;
detecting an amplified output from a power amplifier, the output including a distortion characteristic;
deriving a feedback signal from the amplified output, the feedback signal including a representation of at least a portion of the distortion characteristic;
sampling the feedback signal; and
generating, by a digital predistortion estimator, at least one predistortion coefficient for linearizing the amplified output of the power amplifier based upon a comparison of the sampled feedback signal and the aliased predistorted output signal.
10. The method of claim 9 , further comprising outputting the at least one predistortion coefficient to the digital predistorter.
11. The method of claim 10 , further comprising:
receiving a second digital input signal; and
predistorting the second digital input signal using the at least one predistortion coefficient.
12. The method of claim 11 , wherein predistorting the second RF input signal comprises utilizing an adaptive polynomial-based digital predistortion system, the polynomial-based digital predistortion system utilizing the at least one predistortion coefficient derived by the digital predistortion estimator.
13. The method of claim 11 , wherein predistorting the second RF input signal comprises utilizing a look-up-table-based digital predistortion system with finite impulse response filters, wherein coefficients for the finite impulse response filters comprise the at least one predistortion coefficient derived by the digital predistortion estimator.
14. The method of claim 9 , further comprising aligning the feedback signal relative to the first digital input signal.
15. The method of claim 9 , further comprising converting the feedback signal from analog to digital format.
16. The method of claim 9 , further comprising converting the predistorted output signal from digital to analog format.