Predistortion circuit and method for compensating A/D and other distortion in a digital RF communications transmitter
First Claim
1. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
- providing a digital-to-analog converter (D/A) and an analog-to-digital converter (A/D), said D/A exhibiting higher resolution than said A/D;
digitizing, in said A/D, a first signal output by said D/A;
in response to said first signal, compensating for distortion introduced by said A/D by processing an output of said A/D;
digitizing, in said A/D, a second signal output by analog-transmitter components; and
in response to said second signal, counteracting distortion introduced by said analog-transmitter components by processing said output of said A/D.
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Accused Products
Abstract
A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200, 1800) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Distortion introduced by an analog-to-digital converter (304) may be compensated using a variety of adaptive techniques. Linear distortion is compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).
109 Citations
29 Claims
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1. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
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providing a digital-to-analog converter (D/A) and an analog-to-digital converter (A/D), said D/A exhibiting higher resolution than said A/D;
digitizing, in said A/D, a first signal output by said D/A;
in response to said first signal, compensating for distortion introduced by said A/D by processing an output of said A/D;
digitizing, in said A/D, a second signal output by analog-transmitter components; and
in response to said second signal, counteracting distortion introduced by said analog-transmitter components by processing said output of said A/D. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:
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a digital-to-analog converter (D/A) exhibiting a first resolution and configured to generate a first analog signal;
analog-transmitter components configured to generate a second analog signal;
an analog-to-digital converter (A/D) exhibiting a second resolution less than said first resolution and configured to digitize said first and second analog signals into first and second return-data streams, respectively;
a first compensator configured to process said first return-data stream to compensate for distortion introduced by said A/D; and
a second compensator configured to process said second return-data stream to counteract distortion introduced by said analog-transmitter components. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter using feedback signals monitored by an analog-to-digital converter (A/D) located at said digital communications transmitter, said method comprising:
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a) symmetrizing quantization error introduced by said A/D;
b) compensating for linear distortion introduced by said A/D;
c) compensating for linear distortion introduced by at least a portion of said analog-transmitter components;
d) compensating for nonlinear distortion introduced by said A/D; and
e) compensating for nonlinear distortion introduced by at least a portion of said analog-transmitter components. - View Dependent Claims (26, 27, 28, 29)
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Specification