Methods and apparatus for signal distortion correction
The digital predistorter multiplies the input signal with coefficients obtained from look-up tables. To reduce the amount of storage required, the coefficients are stored in partial form and are either reconstituted by addition of a constant ( 44 , FIG. 3 b ) prior to application to the input signal or the retrieved coefficients are applied directly to the input signal and the resulting modified signal is then combined with the original input signal ( 34 , FIG. 2 a ).
1 - 28 . (canceled)
29 . A method for applying adjustments to signal processing associated with signal handling equipment, the method comprising:
retrieving partial coefficients corresponding to portions of complete coefficients associated with the adjustments; and
applying the partial coefficients to generate the adjustments, wherein corrections are made for the use of the partial coefficients to give the effect that the adjustments have been generated by retrieving and applying complete coefficients.
30 . The invention of claim 29 , wherein:
the signal handling equipment comprises one or more amplifiers; and
the adjustments to the signal processing reduce distortion in an output signal produced by the one or more amplifiers.
31 . The invention of claim 29 , wherein the adjustments to the signal processing correspond to at least one of predistortion of an input signal prior to application to the signal handling equipment and feed-forward distortion correction of an output signal generated by the signal handling equipment.
32 . The invention of claim 31 , wherein the adjustments to the signal processing correspond to the predistortion of the input signal prior to application to the signal handling equipment.
33 . The invention of claim 29 , wherein:
the corrections correspond to a linear part of the adjustments; and
the partial coefficients correspond to deviations from the linear part.
34 . The invention of 33 , wherein:
the linear part corresponds to a coefficient value of one; and
the partial coefficients correspond to deviations of the complete coefficients from the coefficient value of one.
35 . The invention of claim 29 , wherein:
the partial coefficients are applied to a first digital part of an input signal to generate partial adjustments; and
the partial adjustments are combined with complementary adjustments, wherein the complementary adjustments correct for the use of the partial coefficients during the generation of the partial adjustments.
36 . The invention of claim 35 , wherein the first digital part of the input signal corresponds to an in-phase component I of the input signal.
37 . The invention of claim 29 , wherein each partial coefficient is combined with a complementary coefficient prior to being applied to a first digital part of an input signal.
38 . The invention of claim 37 , wherein the first digital part of the input signal corresponds to an in-phase component I of the input signal.
39 . The invention of claim 29 , wherein:
the partial coefficients are retrieved by applying indices to a lookup table; and
at least one of the indices and the partial coefficients are filtered prior to generating the adjustments.
40 . The invention of claim 39 , wherein the filtering applies memory characteristics to the adjustments to the signal processing.
41 . The invention of claim 39 , wherein the filtering is applied to the indices prior to retrieving the partial coefficients.
42 . The invention of claim 29 , wherein:
the partial coefficients correspond to partial adjustments of an in-phase component I of the input signal;
a second set of coefficients corresponding to adjustment of a quadrature-phase component Q of the input signal is retrieved by applying the indices to another lookup table;
a first filter is applied to at least one of the indices and the partial coefficients; and
a second filter is applied to at least one of the indices and the second set of coefficients, wherein the first and second filters apply different memory characteristics to the adjustments to the signal processing.
43 . The invention of claim 42 , wherein the first and second filters are independently applied to the indices prior to retrieving the partial coefficients and the second set of coefficients, respectively.
44 . An apparatus for applying adjustments to signal processing associated with signal handling equipment, the apparatus comprising:
means for retrieving partial coefficients corresponding to portions of complete coefficients associated with the adjustments; and
means for applying the partial coefficients to generate the adjustments, wherein the applying means is adapted to make corrections for the use of the partial coefficients to give an effect that the adjustments have been generated by retrieving and applying the complete coefficients.
45 . An apparatus for applying adjustments to signal processing associated with signal handling equipment, the apparatus comprising:
a first lookup table (LUT) adapted to store partial coefficients corresponding to portions of complete coefficients associated with the adjustments; and
adjustment circuitry adapted to apply the partial coefficients to generate the adjustments, wherein the adjustment circuitry is adapted to make corrections for the use of the partial coefficients to give an effect that the adjustments have been generated by retrieving and applying the complete coefficients.
46 . The invention of claim 45 , wherein:
the signal handling equipment comprises one or more amplifiers; and
the adjustment circuitry is adapted to reduce distortion in an output signal produced by the one or more amplifiers.
47 . The invention of claim 45 , wherein the adjustments to the signal processing correspond to at least one of predistortion of an input signal prior to application to the signal handling equipment and feed-forward distortion correction of an output signal generated by the signal handling equipment.
48 . The invention of claim 47 , wherein the adjustments to the signal processing correspond to the predistortion of the input signal prior to application to the signal handling equipment.
49 . The invention of claim 45 , wherein:
the corrections correspond to a linear part of the adjustments; and
the partial coefficients correspond to deviations from the linear part.
50 . The invention of 49 , wherein:
the linear part corresponds to a coefficient value of one; and
the partial coefficients correspond to deviations of the complete coefficients from the coefficient value of one.
51 . The invention of claim 45 , wherein the adjustment circuitry comprises:
a first multiplier adapted to apply the partial coefficients retrieved from the first LUT to a first digital part of an input signal to generate partial adjustment components; and
one or more combiners ( 34 ) adapted to combine a signal corresponding to the partial adjustment components with the input signal to generate the adjustments.
52 . The invention of claim 51 , wherein the adjustment circuitry further comprises:
a second LUT adapted to store a second set of coefficients associated with the adjustments; and
a second multiplier adapted to apply the second set of coefficients retrieved from the second LUT to a second digital part of the input signal to generate second adjustment components, wherein:
the one or more combiners are adapted to combine the partial adjustment components, the second adjustment components, and the input signal to generate the adjustments.
53 . The invention of claim 52 , wherein:
the first LUT is adapted to store partial I coefficients; and
the second LUT is adapted to store Q coefficients.
54 . The invention of claim 53 , wherein:
the partial I coefficients and the Q coefficients are retrieved from the first and second LUTs based on indices; and
the adjustment circuitry further comprises:
a first filter adapted to filter at least one of the indices and the partial I coefficients; and
a second filter adapted to filter at least one of the indices and the Q coefficients, wherein the first and second filters are adapted to apply different memory characteristics to the adjustments.
55 . The invention of claim 54 , wherein the first and second filters are independently applied to the indices prior to retrieving the partial I coefficients and the Q coefficients, respectively.
56 . The invention of claim 45 , wherein the adjustment circuitry comprises:
a first combiner adapted to combine the partial coefficients retrieved from the first LUT with a constant to generate the complete coefficients; and
a first multiplier adapted to apply the complete coefficients to a first part of an input signal to generate first adjustment components for the adjustments.
57 . The invention of claim 56 , wherein the adjustment circuitry further comprises:
a second LUT adapted to store a second set of coefficients associated with the adjustments;
a second multiplier adapted to apply the second set of coefficients retrieved from the second LUT to a second digital part of the input signal to generate second adjustment components for the adjustments; and
a second combiner adapted to combine the first and second adjustment components to generate the adjustments.
58 . The invention of claim 57 , wherein:
the first lookup table is adapted to store partial I coefficients; and
the second lookup table is adapted to store Q coefficients.
59 . The invention of claim 58 , wherein:
the partial I coefficients and the Q coefficients are retrieved from the first and second LUTs based on indices; and
the adjustment circuitry further comprises:
a first filter adapted to filter at least one of the indices and the partial I coefficients; and
a second filter adapted to filter at least one of the indices and the Q coefficients, wherein the first and second filters are adapted to apply different memory characteristics to the adjustments.
60 . The invention of claim 59 , wherein the first and second filters are independently applied to the indices prior to retrieving the partial I coefficients and the Q coefficients, respectively.
61 . The invention of claim 45 , wherein:
the partial coefficients are retrieved from the first LUT based on indices; and
the adjustment circuitry further comprises a filter adapted to filter at least one of the indices and the partial coefficients.
62 . The invention of claim 61 , wherein the filter is adapted to apply memory characteristics to the adjustments.
63 . The invention of claim 61 , wherein the filter is applied to the indices prior to retrieving the partial coefficients.