Linearity compensator for removing nonlinear distortion
View Patent ↗The present invention is an improved linearizer that implements more complex transfer functions to provide the necessary linearization performance with a reasonable amount of signal processing resources. Particularly, the linearizer operates on an analog-to-digital converter and comprises a distortion compensator and one or more factored Volterra compensators, which may include a second-order factored Volterra compensator, a third-order factored Volterra compensator, and additional higher-order factored Volterra compensators. Inclusion of factored Volterra distortion compensators improves linearization processing performance while significantly reducing the computational complexity compared to a traditional Volterra-based compensator.
1. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprise a second-order factored Volterra compensator.
2. The linearity compensator of claim 1 , wherein the second-order factored Volterra compensator comprises a number of parallel finite impulse response filters and a number of memoryless second order polynomials, wherein the memoryless second order polynomials comprise a second order multiplicative combination of a delayed compensator input signal, wherein the memoryless second order polynomials precede the number of finite impulse response filters.
3. The linearity compensator of claim 2 , wherein the second-order factored Volterra compensator is implemented in a parallel polyphase configuration.
4. The linearity compensator of claim 1 , wherein the electronic system comprises an analog-to-digital converter or a power amplifier.
5. The linearity compensator of claim 1 , wherein the linearity compensator comprises an adaptive nonlinear distortion estimator.
6. The linearity compensator of claim 1 , wherein the factored Volterra compensators comprise a subset of all the factors.
7. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprise a third-order factored Volterra compensator.
8. The linearity compensator of claim 7 , further comprising additional higher-order factored Volterra compensators, wherein the additional higher-order factored Volterra compensators are fourth or higher-order factored Volterra compensators.
9. The linearity compensator of claim 7 , wherein the third-order factored Volterra compensator comprises a number of parallel finite impulse response filters and a number of memoryless third order polynomials, wherein the number of memoryless third order polynomials comprise a third order multiplicative combination of a delayed compensator input signal, wherein the memoryless third order polynomials precede the number of finite impulse response filters.
10. The linearity compensator of claim 9 , wherein the third-order factored Volterra compensator is implemented in a parallel polyphase configuration.
11. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprises a number of linear filters implementing factored Volterra kernels,
wherein the factored Volterra kernels are measured via harmonic probing comprising multi-tone test signals injected into the input of the electronic system.
12. The linearity compensator of claim 11 , wherein a number of tones in the multi-tone test signals is greater than or equal to the order of the corresponding factored Volterra kernel.
13. The linearity compensator of claim 11 , wherein the factored Volterra kernels consist of unique, symmetric Volterra kernels.
14. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprises a number of linear filters implementing factored Volterra kernels,
wherein the factored Volterra kernels are measured via harmonic probing comprising random test tone signals with non-overlapping distortion components.
15. The linearity compensator of claim 14 , wherein the factored Volterra kernels consist of unique, symmetric Volterra kernels.
16. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprises a number of linear filters implementing factored Volterra kernels,
wherein the factored Volterra kernels are calculated using an over-constrained linear least mean square filter design.
17. The linearity compensator of claim 16 , wherein the factored Volterra kernels consist of unique, symmetric Volterra kernels.
18. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the one or more factored Volterra compensators comprises a number of linear filters implementing factored Volterra kernels,
wherein the factored Volterra kernels are calculated using interpolation and extrapolation and inverse fast Fourier transforms.
19. The linearity compensator of claim 18 , wherein the factored Volterra kernels consist of unique, symmetric Volterra kernels.
20. A linearity compensator for removing nonlinear distortion introduced by an electronic system, the linearity compensator comprising:
a distortion compensator; and
one or more factored Volterra compensators,
wherein the distortion compensator comprises:
a first linear filter providing a fundamental signal path and a compensator signal path;
a distortion transfer function operating on the compensator signal path, wherein the distortion transfer function comprises a nonlinear polynomial and a second liner filter; and
an adder for summing the fundamental signal path and the compensator signal path.
21. The linearity compensator of claim 20 , further comprising a bandpass interpolator operating on the compensator signal path.
22. The linearity compensator of claim 21 , wherein the bandpass interpolator comprises an upsampler and a bandpass filter.
23. The linearity compensator of claim 21 , further comprising a downsampler operating on the compensator signal path.
24. The linearity compensator of claim 20 , wherein filter coefficients of the first linear filter are measured by fitting the filter coefficients to a coherently measured amplitude and phase of a transfer function of the distortion transfer function.
25. The linearity compensator of claim 20 , wherein the distortion transfer function further comprises an adaptive nonlinear distortion estimator.
26. The linearity compensator of claim 20 , wherein filter coefficients of the first linear filter are iteratively optimized.
27. The linearity compensator of claim 20 , wherein filter coefficients of the first linear filter are optimized using MINIMAX optimization.
28. The linearity compensator of claim 20 , wherein filter coefficients of the second linear filter are optimized using MINIMAX optimization.
29. The linearity compensator of claim 20 , wherein the factored Volterra kernels consist of unique, symmetric Volterra kernels.