Amplifier linearization by pre-distorting a decomposed input signal
A power amplifier's complex pre-distortion curve is generated by decomposing a representation of an input signal, processing the resulting decomposed signals using analog techniques, and performing signal re-composition. In one implementation, two different halves of a transfer function corresponding to the amplitude characteristics of the amplifier are separately modeled and then combined to generate a control signal used to control a voltage-controlled attenuator that attenuates the input signal, while two different halves of a transfer function corresponding to the amplifier's phase characteristics are separately modeled and then combined to generate a different control signal used to control a voltage-controlled phase shifter that adjusts the phase of the input signal. The resulting output signal corresponds to an amplitude-and-phase pre-distorted signal that can be applied to linearize a corresponding (high power) amplifier.
1. A method for pre-distorting an input signal, comprising:
generating, based on the input signal, a first signal corresponding to a first portion of a first transfer function, wherein the first portion of the first transfer function corresponds to a first voltage range of the input signal;
generating, based on the input signal, a second signal corresponding to a second portion of the first transfer function, wherein the second portion of the first transfer function corresponds to a second voltage range of the input signal different from the first voltage range of the input signal;
combining the first and second signals to generate a first combined signal corresponding to the first transfer function; and
pre-distorting the input signal based on the first combined signal.
2. The invention of claim 1 , wherein:
the first transfer function corresponds to amplitude characteristics of an amplifier; and
the amplitude of the input signal is adjusted based on the first combined signal.
3. The invention of claim 1 , wherein:
the first transfer function corresponds to phase characteristics of an amplifier; and
the phase of the input signal is adjusted based on the first combined signal.
4. The invention of claim 3 , further comprising:
generating, based on the input signal, a third signal corresponding to a first portion of a second transfer function corresponding to amplitude characteristics of the amplifier;
generating, based on the input signal, a fourth signal corresponding to a second portion of the second transfer function;
combining the third and fourth signals to generate a second combined signal corresponding to the second transfer function; and
adjusting the amplitude of the input signal based on the second combined signal.
5. The invention of claim 4 , further comprising detecting the envelope of the input signal, wherein:
the first and second signals are generated based on the envelope-detected input signal;
the first signal is generated by DC-shifting the envelope-detected input signal; and
the first and second signals are generated using different non-linear analog circuits that model different portions of the first transfer function.
6. The invention of claim 1 , further comprising detecting the envelope of the input signal, wherein the first and second signals are generated based on the envelope-detected input signal.
7. The invention of claim 6 , wherein the first signal is generated by DC-shifting the envelope-detected input signal.
8. The invention of claim 1 , wherein the first and second signals are generated using different non-linear analog circuits that model different portions of the first transfer function.
9. The invention of claim 1 , further comprising:
differentiating a first portion of the first combined signal to generate a differentiated signal; and
combining the differentiated signal with a second portion of the first combined signal to generate a frequency-dependent combined signal, wherein the input signal is pre-distorted based on the frequency-dependent combined signal.
10. The invention of claim 1 , further comprising:
generating a frequency-dependent pre-distortion signal; and
combining the frequency-dependent pre-distortion signal with the first combined signal to generate a frequency-dependent combined signal, wherein the input signal is pre-distorted based on the frequency-dependent combined signal.
11. An apparatus for pre-distorting an input signal, comprising:
means for generating, based on the input signal, a first signal corresponding to a first portion of a first transfer function, wherein the first portion of the first transfer function corresponds to a first voltage range of the input signal;
means for generating, based on the input signal, a second signal corresponding to a second portion of the first transfer function, wherein the second portion of the first transfer function corresponds to a second voltage range of the input signal different from the first voltage range of the input signal;
means for combining the first and second signals to generate a first combined signal corresponding to the first transfer function; and
means for pre-distorting the input signal based on the first combined signal.
12. The invention of claim 11 , wherein:
the first transfer function corresponds to amplitude characteristics of an amplifier; and
the amplitude of the input signal is adjusted based on the first combined signal.
13. The invention of claim 11 , wherein:
the first transfer function corresponds to phase characteristics of an amplifier; and
the phase of the input signal is adjusted based on the first combined signal.
14. The invention of claim 13 , further comprising:
means for generating, based on the input signal, a third signal corresponding to a first portion of a second transfer function corresponding to amplitude characteristics of the amplifier;
means for generating, based on the input signal, a fourth signal corresponding to a second portion of the second transfer function;
means for combining the third and fourth signals to generate a second combined signal corresponding to the second transfer function; and
means for adjusting the amplitude of the input signal based on the second combined signal.
15. An apparatus for pre-distorting an input signal, comprising:
a main signal path comprising a first element adapted to pre-distort the input signal based on a first control signal; and
a control signal path adapted to generate the first control signal and comprising:
an envelope detector adapted to detect the envelope of the input signal;
a DC-level-shifting circuit adapted to DC-shift a first copy of the envelope-detected input signal;
a first non-linear circuit adapted to generate, based on the DC-shifted, envelope-detected input signal, a first signal corresponding to a first portion of a first transfer function;
a second non-linear circuit adapted to generate, based on a second copy of the envelope-detected input signal, a second signal corresponding to a second portion of the first transfer function; and
a first combiner adapted to combine the first and second signals to generate a first combined signal corresponding to the first transfer function, wherein the first control signal is based on the first combined signal.
16. The invention of claim 15 , wherein:
the first transfer function corresponds to amplitude characteristics of an amplifier; and
the first element is an attenuator adapted to adjust the amplitude of the input signal based on the first control signal.
17. The invention of claim 15 , wherein:
the first transfer function corresponds to phase characteristics of an amplifier; and
the first element is a phase adjuster adapted to adjust the phase of the input signal based on the first control signal.
18. The invention of claim 17 , wherein:
the main signal path further comprises an attenuator adapted to adjust the amplitude of the input signal based on a second control signal; and
the control signal path is further adapted to generate the second control signal and further comprises:
a third non-linear circuit adapted to generate, based on the DC-shifted, envelope-detected input signal, a third signal corresponding to a first portion of a second transfer function corresponding to amplitude characteristics of the amplifier;
a fourth non-linear circuit adapted to generate, based on the envelope-detected input signal, a fourth signal corresponding to a second portion of the second transfer function; and
a second combiner adapted to combine the third and fourth signals to generate a second combined signal corresponding to the second transfer function, wherein the second control signal is based on the second combined signal.
19. The invention of claim 18 , wherein the first and second non-linear circuits are analog circuits.
20. The invention of claim 15 , wherein the first and second non-linear circuits are analog circuits.
21. The invention of claim 15 , wherein the control signal path further comprises:
a differentiator adapted to differentiate a first portion of the first combined signal to generate a differentiated signal; and
a second combiner adapted to combine the differentiated signal with a second portion of the first combined signal to generate a frequency-dependent combined signal, wherein the first control signal is based on the frequency-dependent combined signal.
22. The invention of claim 15 , further comprising:
an additional set of circuitry adapted to generate a frequency-dependent pre-distortion signal; and
a second combiner adapted to combine the frequency-dependent pre-distortion signal with the first combined signal to generate a frequency-dependent combined signal, wherein the first control signal is based on the frequency-dependent combined signal.
23. A method for pre-distorting an input signal, comprising:
detecting the envelope of the input signal;
generating, by DC-shifting the envelope-detected input signal, a first signal corresponding to a first portion of a first transfer function;
generating, based on the envelope-detected input signal, a second signal corresponding to a second portion of the first transfer function;
combining the first and second signals to generate a first combined signal corresponding to the first transfer function; and
pre-distorting the input signal based on the first combined signal.
24. A method for pre-distorting an input signal, comprising:
generating, based on the input signal, a first signal corresponding to a first portion of a first transfer function;
generating, based on the input signal, a second signal corresponding to a second portion of the first transfer function;
combining the first and second signals to generate a first combined signal corresponding to the first transfer function;
differentiating a first portion of the first combined signal to generate a differentiated signal;
combining the differentiated signal with a second portion of the first combined signal to generate a frequency-dependent combined signal; and
pre-distorting the input signal based on the frequency-dependent combined signal.
25. A method for pre-distorting an input signal, comprising:
generating, based on the input signal, a first signal corresponding to a first portion of a first transfer function;
generating, based on the input signal, a second signal corresponding to a second portion of the first transfer function;
combining the first and second signals to generate a first combined signal corresponding to the first transfer function;
generating a frequency-dependent pre-distortion signal;
combining the frequency-dependent pre-distortion signal with the first combined signal to generate a frequency-dependent combined signal; and
pre-distorting the input signal based on the frequency-dependent combined signal.