Frequency-based predistortion signal generation
An apparatus is disclosed for frequency-based predistortion signal generation. In an example aspect, the apparatus includes a predistortion linearizer circuit configured to be coupled to an input of an amplifier. The amplifier has non-linearities associated with multiple frequencies. The multiple frequencies include a first subset of frequencies and a second subset of frequencies. The predistortion linearizer circuit is also configured to accept an input signal. The predistortion linearizer circuit is additionally configured to generate, based on the input signal, a compensation signal to attenuate the non-linearities existing within the first subset of frequencies more than the non-linearities existing within the second subset of frequencies. The predistortion linearizer circuit is further configured to generate a pre-distorted signal based on the input signal and the compensation signal.
1. An apparatus comprising:
a predistortion linearizer circuit configured to:
be coupled to an input of an amplifier, the amplifier having non-linearities associated with multiple frequencies, the multiple frequencies comprising a first subset of frequencies and a second subset of frequencies;
accept an input signal;
generate, based on the input signal, a compensation signal to attenuate the non-linearities existing within the first subset of frequencies more than the non-linearities existing within the second subset of frequencies; and
generate a pre-distorted signal based on the input signal and the compensation signal, wherein the predistortion linearizer circuit is configured to:
apply weights to the input signal to generate a weighted input signal; and
apply a waveform-shaping function to the weighted input signal to generate the compensation signal.
2. The apparatus of claim 1 , further comprising:
the amplifier configured to amplify a version of the pre-distorted signal.
3. The apparatus of claim 1 , wherein:
the first subset of frequencies comprises frequencies that are above or below an allocated bandwidth associated with the input signal; and
the second subset of frequencies comprises frequencies that are within the allocated bandwidth.
4. The apparatus of claim 3 , wherein:
the allocated bandwidth is associated with a set of allocated resource blocks within a frequency band; and
the first subset of frequencies is associated with a set of non-allocated resource blocks within the frequency band.
5. The apparatus of claim 4 , further comprising:
a wireless transceiver, the wireless transceiver comprising the predistortion linearizer circuit and configured to satisfy, based on the compensation signal, at least one in-band emissions target associated with the first subset of frequencies.
6. The apparatus of claim 3 , wherein:
the allocated bandwidth is associated with a set of allocated resource blocks within a frequency band; and
the first subset of frequencies is associated with another frequency band that is adjacent to the frequency band.
7. The apparatus of claim 6 , further comprising:
a wireless transceiver, the wireless transceiver comprising the predistortion linearizer circuit and configured to satisfy, based on the compensation signal, at least one adjacent channel leakage ratio target associated with the first subset of frequencies.
8. The apparatus of claim 1 , wherein the predistortion linearizer circuit is further configured to generate, based on the input signal, the compensation signal to attenuate the non-linearities existing within the first subset of frequencies without substantially attenuating the non-linearities existing within the second subset of frequencies.
9. The apparatus of claim 1 , wherein a shape of an amplitude of the compensation signal differs between the first subset of frequencies and the second subset of frequencies.
10. The apparatus of claim 9 , wherein an average amplitude of the compensation signal is greater across the first subset of frequencies relative to the second subset of frequencies.
11. The apparatus of claim 9 , wherein the shape of the amplitude of the compensation signal further varies within at least one of the following:
the first subset of frequencies; or
the second subset of frequencies.
12. The apparatus of claim 1 , wherein:
the first subset of frequencies comprises frequencies that are within an allocated bandwidth associated with the input signal; and
the second subset of frequencies comprises frequencies that are above or below the allocated bandwidth.
13. The apparatus of claim 12 , wherein:
the allocated bandwidth is associated with a set of allocated resource blocks within a frequency band; and
the second subset of frequencies is associated with at least one of the following:
a set of non-allocated resource blocks within the frequency band; or
another frequency band that is adjacent to the frequency band.
14. The apparatus of claim 13 , further comprising:
a wireless transceiver, the wireless transceiver comprising the predistortion linearizer circuit and configured to satisfy, based on the compensation signal, at least one error vector magnitude target associated with the input signal.
15. The apparatus of claim 1 , wherein an amplitude of the waveform-shaping function differs between the first subset of frequencies and the second subset of frequencies.
16. The apparatus of claim 15 , wherein an average amplitude of the waveform-shaping function is greater across the first subset of frequencies relative to the second subset of frequencies.
17. The apparatus of claim 1 , wherein the predistortion linearizer circuit is configured to:
accept another input signal;
generate, based on the other input signal, another compensation signal to attenuate the non-linearities existing within the second subset of frequencies more than the non-linearities existing within the first subset of frequencies; and
generate another pre-distorted signal based on the other input signal and the other compensation signal.
18. The apparatus of claim 1 , wherein:
the amplifier comprises a power amplifier; and
an operating point of the power amplifier is substantially proximate to a saturation point.
19. The apparatus of claim 18 , wherein the operating point of the power amplifier is within approximately 7 decibels of the saturation point.
20. The apparatus of claim 1 , wherein the predistortion linearizer circuit comprises:
a weight estimation circuit configured to:
be coupled to the input of the amplifier and an output of the amplifier; and
generate the weights that characterize the non-linearities of the amplifier; and
a waveform generation circuit configured to:
be coupled to the input of the amplifier;
accept the input signal;
apply the weights to the input signal to generate the compensation signal; and
generate the pre-distorted signal based on the compensation signal and the input signal.
21. The apparatus of claim 20 , wherein the waveform generation circuit comprises:
a summation circuit coupled to the input of the amplifier, the summation circuit configured to combine the input signal with an inverse of the compensation signal to generate the pre-distorted signal;
a combiner circuit configured to generate the weighted input signal based on the input signal and the weights; and
a frequency-selective waveform shaper configured to:
perform a Fourier transform operation on the weighted input signal;
apply a waveform-shaping function to the transformed version of the weighted input signal; and
perform an inverse Fourier transform operation to generate the compensation signal.
22. The apparatus of claim 1 , wherein the predistortion linearizer circuit is configured to maintain amplitudes of the non-linearities within the second subset of frequencies to be above a threshold.
23. An apparatus comprising:
means for amplifying a pre-distorted signal, the means having non-linearities associated with multiple frequencies, the multiple frequencies comprising in-band frequencies and out-of-band frequencies; and
means for attenuating the non-linearities existing within the in-band frequencies by a first amount and attenuating the non-linearities existing within the out-of-band frequencies by a second amount greater than the first amount.
24. The apparatus of claim 23 , wherein the means for attenuating the non-linearities comprises means for generating a compensation signal having an amplitude with a shape that varies between the in-band frequencies and the out-of-band frequencies.
25. A method for performing frequency-based predistortion signal generation, the method comprising:
applying weights to an input signal to generate a weighted input signal;
apply a waveform-shaping function to the weighted input signal;
generating, based at least on the weighted input signal, a compensation signal to attenuate non-linearities existing within a first subset of frequencies more than other non-linearities existing within a second subset of frequencies, the non-linearities and the other non-linearities associated with an amplifier;
generating a pre-distorted signal based on the input signal and the compensation signal; and
passing the pre-distorted signal to an input of the amplifier.
26. The method of claim 25 , wherein the generating of the compensation signal comprises generating, based on the input signal, the compensation signal to attenuate the non-linearities existing within the first subset of frequencies without substantially attenuating the non-linearities existing within the second subset of frequencies.
27. The method of claim 25 , wherein a shape of an amplitude of the compensation signal differs between the first subset of frequencies and the second subset of frequencies.
28. The method of claim 25 , wherein:
the first subset of frequencies comprises frequencies that are above or below an allocated bandwidth associated with the input signal; and
the second subset of frequencies comprises frequencies that are within the allocated bandwidth.
29. The method of claim 25 , wherein:
the first subset of frequencies comprises frequencies that are within an allocated bandwidth associated with the input signal; and
the second subset of frequencies comprises frequencies that are above or below the allocated bandwidth.
30. The method of claim 25 , further comprising:
accepting another input signal;
generating, based on the other input signal, another compensation signal to attenuate the other non-linearities existing within the second subset of frequencies more than the non-linearities existing within the first subset of frequencies;
generating another pre-distorted signal based on the other input signal and the other compensation signal; and
passing the other pre-distorted signal to the input of the amplifier.
31. An apparatus comprising:
a predistortion linearizer circuit operably coupled to an input of an amplifier, the amplifier having non-linearities associated with multiple frequencies, the multiple frequencies comprising in-band frequencies and out-of-band frequencies, the predistortion linearizer circuit configured to attenuate the non-linearities existing within the in-band frequencies by a first amount and attenuate the non-linearities existing within the out-of-band frequencies by a second amount greater than the first amount.
32. The apparatus of claim 31 , wherein:
the in-band frequencies comprise a set of allocated resource blocks within a frequency band; and
the out-of-band frequencies comprise at least one of the following:
a set of non-allocated resource blocks within the frequency band; or
frequencies associated with another frequency band that is adjacent to the frequency band.
33. The apparatus of claim 31 , wherein the predistortion linearizer circuit is configured to attenuate the non-linearities within the out-of-band frequencies by a same amount.
34. The apparatus of claim 31 , wherein the predistortion linearizer circuit is configured to attenuate the non-linearities within the out-of-band frequencies by different amounts such that a portion of the non-linearities within the out-of-band frequencies that are closer to the in-band frequencies are attenuated by a larger amount than another portion of the non-linearities within the out-of-band frequencies that are farther from the in-band frequencies.
35. The apparatus of claim 31 , wherein the first amount of attenuation and the second amount of attenuation are defined by a waveform-shaping function having an varying amplitude that differs between the in-band frequencies and the out-of-band frequencies.
36. The apparatus of claim 31 , wherein the predistortion linearizer circuit is configured to attenuate the non-linearities within the in-band frequencies by different amounts such that a portion of the non-linearities within the in-band frequencies that are closer to the out-of-band frequencies are attenuated by a larger amount than another portion of the non-linearities within the in-band frequencies that are farther from the out-of-band frequencies.
37. An apparatus comprising:
a radio-frequency front-end circuit configured to be coupled to an antenna, the radio-frequency front-end circuit comprising an amplifier configured to generate, based on a pre-distorted signal, an amplified signal having non-linearities within in-band frequencies that are attenuated by a first amount and non-linearities within out-of-band frequencies that are attenuated by a second amount greater than the first amount; and
a predistortion linearizer circuit operably coupled to an input of the amplifier and configured to generate the pre-distorted signal.
38. The apparatus of claim 37 , further comprising a modem operably coupled to the radio-frequency front-end circuit,
wherein the modem comprises the predistortion linearizer circuit.
39. The apparatus of claim 37 , further comprising a transceiver circuit operably coupled to the radio-frequency front-end circuit,
wherein the transceiver circuit comprises the predistortion linearizer circuit.
40. The apparatus of claim 37 , wherein the first amount of attenuation and the second amount of attenuation are defined by a waveform-shaping function having an varying amplitude that differs between the in-band frequencies and the out-of-band frequencies.
41. An apparatus comprising:
a predistortion linearizer circuit configured to:
be coupled to an input of an amplifier, the amplifier having non-linearities associated with multiple frequencies, the multiple frequencies comprising a first subset of frequencies and a second subset of frequencies;
accept an input signal;
generate, based on the input signal, a compensation signal to attenuate the non-linearities existing within the first subset of frequencies more than the non-linearities existing within the second subset of frequencies; and
generate a pre-distorted signal based on the input signal and the compensation signal, wherein the predistortion linearizer circuit comprises:
a weight estimation circuit configured to:
be coupled to the input of the amplifier and an output of the amplifier; and
generate weights that characterize the non-linearities of the amplifier; and
a waveform generation circuit configured to:
be coupled to the input of the amplifier;
accept the input signal;
apply the weights to the input signal to generate the compensation signal; and
generate the pre-distorted signal based on the compensation signal and the input signal.
42. The apparatus of claim 41 , wherein the waveform generation circuit comprises:
a summation circuit coupled to the input of the amplifier, the summation circuit configured to combine the input signal with an inverse of the compensation signal to generate the pre-distorted signal;
a combiner circuit configured to generate a weighted input signal based on the input signal and the weights; and
a frequency-selective waveform shaper configured to:
perform a Fourier transform operation on the weighted input signal;
apply a waveform-shaping function to the transformed version of the weighted input signal; and
perform an inverse Fourier transform operation to generate the compensation signal.