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 radio frequency (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 plurality of polynomial blocks operable to determine a plurality of polynomial coefficients using the baseband signal;
a vector modulator coupled to the RF output and operable to apply the plurality of polynomial coefficients to the RF output; and
an adaptation algorithm unit operable to optimize predistortion components using the plurality of polynomial coefficients.
2. The wideband predistortion system of claim 1 , wherein the vector modulator comprises a plurality of delayed and summed vector modulators.
3. The wideband predistortion system of claim 1 , wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
4. The wideband predistortion system of claim 1 , further comprising a digital delay block coupled to the adaptation algorithm unit.
5. The wideband predistortion system of claim 4 , wherein the digital delay block comprises an equalizer.
6. A wideband predistortion system for use with radio frequency (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 plurality of polynomial blocks operable to determine a plurality of polynomial coefficients using the baseband signal; and
a vector modulator coupled to the RF output and operable to apply the plurality of polynomial coefficients to the RF output.
7. The wideband predistortion system of claim 6 , wherein the vector modulator comprises a plurality of delayed and summed vector modulators.
8. The wideband predistortion system of claim 6 , wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
9. The wideband predistortion system of claim 6 , further comprising a digital delay block coupled to the adaptation algorithm unit.
10. The wideband predistortion system of claim 9 , wherein the digital delay block comprises an equalizer.
11. A method for compensating for memory effects in a wideband predistortion system, the method comprising:
receiving a baseband signal at a baseband input;
determining a plurality of polynomial coefficients at a plurality of polynomial blocks, using the baseband signal;
applying the plurality of polynomial coefficients to an RF output, using a vector modulator coupled to the RF output;
providing the RF output to an RF power amplifier; and
optimizing predistortion components at an adaptation algorithm unit coupled to the RF power amplifier, using the plurality of polynomial coefficients.
12. The method of claim 11 , wherein the vector modulator comprises a plurality of delayed and summed vector modulators.
13. The method of claim 11 , wherein the vector modulator comprises a variable attenuator and a variable phase shifter.