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 comprising:
a baseband input for receiving a baseband signal,
an RF output for providing a signal to an RF power amplifier,
logic for deriving a predistortion function from the baseband signal and generating a predistortion signal, wherein the logic comprises a polynomial calculation, and
a vector modulator responsive to the predistortion function and connected to the RF output for applying the predistortion signal to the RF output.
2. The wideband predistortion system of claim 1 wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
3. The wideband predistortion system of claim 1 wherein the baseband signal is at an Intermediate Frequency.
4. The wideband predistortion system of claim 1 wherein the baseband signal is output using a digital to analog converter for a quadrature component and for an in-phase component.
5. The wideband predistortion system of claim 1 wherein the baseband signal is frequency translated to a RF frequency using a quadrature modulator.
6. The wideband predistortion system of claim 1 further comprising a digital delay block.
7. The wideband predistortion system of claim 6 wherein the digital delay block comprises an equalizer.
8. A wideband predistortion system for use with RF power amplifiers, the system comprising:
a baseband input for receiving a baseband signal, wherein the baseband signal is frequency translated to an RF frequency using a quadrature modulator;
an RF output for providing a signal to an RF power amplifier;
logic for deriving a predistortion function from the baseband signal and generating a predistortion signal, wherein the logic comprises a lookup table; and
a vector modulator responsive to the predistortion function and connected to the RF output for applying the predistortion signal to the RF output.
9. The wideband predistortion system of claim 8 wherein the vector modulator comprises a variable attenuator and a variable phase shifter.
10. The wideband predistortion system of claim 8 wherein the baseband signal is at an Intermediate Frequency.
11. The wideband predistortion system of claim 8 wherein the baseband signal is output using a digital to analog converter for a quadrature component and for an in-phase component.
12. The wideband predistortion system of claim 8 further comprising a digital delay block.
13. The wideband predistortion system of claim 12 wherein the digital delay block comprises an equalizer.