Baseband-derived RF digital predistortion
A baseband-derived RF predistortion system using a lookup table having coefficients extracted at baseband and then applied at RF by means of a vector modulator. The architecture combines the narrowband advantage of envelope predistortion with the accuracy of baseband predistortion, and including compensation for memory effects. A polynomial-based alternative is also described.
1. A wideband predistortion system for use with RF power amplifiers, the system comprising:
a baseband input operable to receive a baseband signal;
an RF output operable to provide a signal to an RF power amplifier;
a lookup table including a predistortion signal including predistortion components;
a vector modulator coupled to the RF output and operable to apply the predistortion signal to the RF output; and
an adaptation algorithm unit operable to optimize the predistortion components.
2. The wideband predistortion system of claim 1 wherein the predistortion signal includes predistortion coefficients based on a difference between the baseband signal and a feedback signal derived from the RF output.
3. The wideband predistortion system of claim 1 wherein the vector modulator comprises a plurality of delayed and summed vector modulators.
4. The wideband predistortion system of claim 1 wherein the lookup table is indexed by a square of a magnitude of the baseband signal.
5. The wideband predistortion system of claim 1 further comprising a quadrature modulator coupled to the baseband input and operable to receive the baseband signal and translate the baseband signal to an RF frequency.
6. The wideband predistortion system of claim 1 wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
7. The wideband predistortion system of claim 1 further comprising a digital delay block coupled to the adaptation algorithm unit.
8. The wideband predistortion system of claim 7 wherein the digital delay block comprises an equalizer.
9. A wideband predistortion system for use with RF power amplifiers, the system comprising:
a baseband input operable to receive a baseband signal;
a quadrature modulator coupled to the baseband input and operable to receive the baseband signal and translate the baseband signal to an RF frequency;
an RF output operable to provide a signal to an RF power amplifier;
a vector modulator coupled to the RF output and operable to apply the predistortion signal to the RF output, the vector modulator comprising a plurality of delayed and summed vector modulators; and
a lookup table coupled to the vector modulator and including a predistortion signal including predistortion components.
10. The wideband predistortion system of claim 9 wherein the lookup table is indexed by a square of a magnitude of the baseband signal.
11. The wideband predistortion system of claim 9 wherein the predistortion coefficients are based on a difference between the baseband signal and a feedback signal derived from the RF output.
12. The wideband predistortion system of claim 9 wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
13. The wideband predistortion system of claim 9 further comprising a digital delay block coupled to the quadrature modulator.
14. The wideband predistortion system of claim 13 wherein the digital delay block comprises an equalizer.