Additive pre-distortion for linearization
View Patent ↗In one embodiment, a signal processor for linearizing a non-linear circuit through pre-distortion of an input signal is provided that includes: a first coupler for extracting a version of the input signal, wherein a remaining portion of the input signal not extracted by the first coupler is provided to a first node; a mixer for multiplying the extracted version of the input signal with a pre-distortion signal to produce an additive signal, the pre-distortion signal having a relatively small or zero constant component such that the additive signal includes either no linear version of the input signal or a linear version of the input signal that has a lower power than the remaining portion of the input signal; and a second coupler to add the additive signal to the remaining portion of the input signal at the first node to form a pre-distorted input signal, whereby if the non-linear circuit processes the pre-distorted input signal to form an output signal, the output signal is a substantially linear function of the input signal.
1. A signal processor for linearizing a non-linear circuit through pre-distortion of an input signal to form a pre-distorted input signal, the non-linear circuit processing the pre-distorted input signal to provide an output signal, comprising:
a first coupler for extracting a version of the input signal, wherein a remaining portion of the input signal not extracted by the first coupler is provided to a first node;
a mixer for multiplying the version of the input signal with a pre-distortion signal to produce an additive signal, the pre-distortion signal having a relatively small or zero constant component such that the additive signal includes either no linear version of the input signal or a linear version of the input signal that has a lower power than the remaining portion of the input signal; and
a second coupler to add the additive signal to the remaining version of the input signal at the first node to form the pre-distorted input signal, whereby the output signal is substantially linearly related to the input signal.
2. The signal processor of claim 1 , further comprising:
a quadrature phase-shifter (QPS) to form an in-phase portion of the version of the input signal and a quadrature portion of the version of the input signal, wherein the mixer comprises an in-phase mixer for mixing the in-phase portion with an in-phase version of the pre-distortion signal to provide an in-phase output signal and a quadrature-phase mixer for mixing the quadrature-phase portion with a quadrature-phase version of the pre-distortion signal to provide a quadrature-phase output signal, and
a combiner for combining the in-phase and quadrature-phase output signals to form the additive signal.
3. The signal processor of claim 2 , further comprising a buffer to buffer the version of the input signal provided to the QPS.
4. The signal processor of claim 1 , wherein the non-linear circuit is an amplifier.
5. The signal processor of claim 1 , wherein the non-linear circuit is a mixer.
6. The signal processor of claim 1 , further comprising a signal generator, the signal generator being adapted to receive a version of the output signal from the non-linear circuit and a version of the input signal so that the signal generator may determine the non-linearity of the non-linear circuit, the signal generator being further adapted to generate the pre-distortion signal so that the non-linearity is substantially eliminated.
7. The signal processor of claim 1 , further comprising:
means for forming an in-phase portion of the version of the input signal and a quadrature portion of the version of the input signal, wherein the mixer comprises an in-phase mixer for mixing the in-phase portion with an in-phase version of the pre-distortion signal to provide an in-phase output signal and a quadrature-phase mixer for mixing the quadrature-phase portion with a quadrature-phase version of the pre-distortion signal to provide a quadrature-phase output signal, and
a combiner for combining the in-phase and quadrature-phase output signals to form the additive signal.
8. The signal processor of claim 7 , wherein the non-linear circuit is an amplifier.
9. The signal processor of claim 7 , wherein the non-linear circuit is a mixer.
10. The signal processor of claim 7 , further comprising a signal generator, the signal generator being adapted to receive a version of the output signal from the non-linear circuit and a version of the input signal so that the signal generator may determine the non-linearity of the non-linear circuit, the signal generator being further adapted to generate the pre-distortion signal so that the non-linearity is substantially eliminated.
11. A signal processor for linearizing a non-linear circuit through pre-distortion of an input signal, comprising:
a first coupler for extracting a version of the input signal;
a variable gain amplifier adapted to receive a remaining portion of input signal not extracted by the first coupler to provide a gain-adjusted version of the input signal;
a mixer for mixing the version of the input signal from the first coupler with a pre-distortion signal to produce an additive signal, the pre-distortion signal having a relatively small or zero constant component such that the additive signal includes either no linear version of the input signal or a linear version of the input signal that has a lower power than the remaining portion of the input signal; and
a second coupler to add the additive signal to the gain-adjusted version of the input signal to form a pre-distorted input signal, whereby if the non-linear circuit processes the pre-distorted input signal to form an output signal, the output signal is a substantially linear function of the input signal.
12. A method of linearizing a non-linear circuit, comprising:
generating an error signal based upon a non-linearity in an output signal from the non-linear circuit;
generating a pre-distortion signal responsive to the error signal;
multiplying a version of the input signal with the pre-distortion signal to produce a multiplied signal, the pre-distortion signal having no constant component such that the multiplication produces no linear versions of the input signal;
adding the multiplied signal to the input signal to provide a pre-distorted input signal; and
processing the pre-distorted input signal through the non-linear circuit to provide the output signal that is a substantially linear function of the input signal.
13. The method of claim 12 , wherein the non-linear circuit is an amplifier, the output signal thereby being a substantially linearly amplified version of the input signal.
14. The method of claim 13 , wherein the amplifier comprises a cascade of a plurality of amplifiers arranged from a first amplifier to a last amplifier such that each successive amplifier amplifies an output signal from an immediately-preceding amplifier.
15. The method of claim 14 , wherein the cascade of a plurality of amplifiers forms a power amplifier for a cellular base station.
16. The method of claim 12 , wherein the non-linear circuit is a mixer, the output signal thereby being a substantially linearly multiplied version of the input signal.
17. The method of claim 12 , wherein the input signal includes an envelope modulation, the pre-distortion signal being a series expression of various powers of the envelope modulation.