Constant gain digital predistortion controller for linearization of non-linear amplifiers
First Claim
1. A method of stabilizing a predistortion function that is stored in a lookup table, wherein at least a portion of the predistortion function is approximately complementary to a transfer function of a power amplifier, the method comprising:
- identifying a portion of the lookup table that corresponds to a region of unrealizable system gain;
scaling entries from the identified portion of the lookup table such that the overall gain of the predistortion function in the identified portion of the lookup table is reduced; and
storing the scaled entries back into the lookup table.
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Abstract
The invention is related to methods and apparatus for controlling and adapting a digital predistortion linearizer for amplification of bandlimited signals using non-linear amplifiers. The control method advantageously permits the predistortion function applied by a predistortion entity to provide a relatively constant gain. This attribute is advantageous for operation within cellular radio systems, which often employ digital power control systems. However, the disclosed techniques can also be applicable to virtually any type of digital predistortion for which an input signal or reference signal to be amplified is predistorted in a manner that is complementary to the distortion induced by a non-linear amplifier. Embodiments of the invention advantageously enhance the practicality of using digital linearization and predistortion amplification techniques. Embodiments of the invention can automatically adjust the characteristics of a predistorted signal so that a deviation from overall linearity is compensated and subsequently reduced while maintaining a nearly constant gain attribute.
162 Citations
18 Claims
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1. A method of stabilizing a predistortion function that is stored in a lookup table, wherein at least a portion of the predistortion function is approximately complementary to a transfer function of a power amplifier, the method comprising:
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identifying a portion of the lookup table that corresponds to a region of unrealizable system gain; scaling entries from the identified portion of the lookup table such that the overall gain of the predistortion function in the identified portion of the lookup table is reduced; and storing the scaled entries back into the lookup table. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for stabilizing a predistortion function that is stored in a lookup table, wherein at least a portion of the predistortion function is approximately complementary to a transfer function of a power amplifier, the apparatus comprising:
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means for identifying a portion of the lookup table that corresponds to a region of unrealizable system gain; means for scaling entries from the identified portion of the lookup table such that the overall gain of the predistortion function in the identified portion of the lookup table is reduced; and means for storing the scaled entries back into the lookup table. - View Dependent Claims (11, 12, 13)
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14. An apparatus for stabilizing a predistortion function that is stored in a lookup table, wherein at least a portion of the predistortion function is approximately complementary to a transfer function of a power amplifier, the apparatus comprising:
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a circuit configured to identify a portion of the lookup table that corresponds to a region of unrealizable system gain; a circuit configured to scale entries from the identified portion of the lookup table such that the overall gain of the predistortion function in the identified portion of the lookup table is reduced; and a circuit configured to store the scaled entries back into the lookup table. - View Dependent Claims (15, 16, 17, 18)
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Specification