Under-Sampled Digital Predistortion for Power Amplifier Linearity
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Solution Overview
Problem
Power amplifiers in wireless communication systems suffer from nonlinearity, leading to distortions and increased power consumption, especially as required bandwidth increases, making it difficult and costly to compensate for these issues.
Innovation Solution
A system with a predistorter, first and second converters, and a power amplifier, where the second converter undersamples the output signal at a lower frequency to generate a feedback signal, allowing the predistorter to estimate and counteract distortion using polynomial-based filters and adaptive algorithms to compensate for nonlinearity and memory effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If additional circuit components are added to compensate for nonlinearity in power amplifiers, then distortion in output signals is reduced, but power consumption increases
Solution Approach 1:
The patent creates a digital model (copy) of the power amplifier's nonlinear behavior through polynomial-based predistortion filters. This virtual model allows the system to compensate for nonlinearity through signal processing rather than adding physical compensation circuits, thereby reducing power consumption while maintaining signal linearity.
Solution Approach 2:
The patent replaces analog compensation circuits with digital signal processing techniques. By using digital predistortion filters and polynomial-based models to compensate for nonlinearity, the system substitutes complex analog circuitry with computationally efficient digital algorithms, reducing overall power consumption.
2Speed
If bandwidth increases to support high speed communication applications, then communication speed is improved, but compensation for nonlinearity becomes more difficult and expensive
Solution Approach 1:
The patent employs polynomial-based predistortion filters with adjustable parameters that can be optimized for different bandwidth requirements. By changing the polynomial order and filter parameters, the system can adapt to various communication speeds and bandwidths without requiring fundamentally different compensation architectures, thereby managing complexity effectively.
Solution Approach 2:
The patent creates a universal compensation framework using polynomial-based filters that can handle multiple bandwidth scenarios and communication standards. The same predistortion architecture serves various high-speed communication applications, reducing the need for application-specific complex compensation circuits.
3Use of energy by moving object
If sampling frequency is reduced to lower power consumption, then power consumption is reduced, but distortion estimation accuracy may be degraded
Solution Approach 1:
The patent applies predistortion to the input signal before amplification, preemptively compensating for expected nonlinear distortions. This preliminary action reduces the burden on feedback sampling, allowing accurate distortion estimation even at lower sampling frequencies because the majority of compensation is already performed in advance.
Solution Approach 2:
The patent creates a digital model of the amplifier's nonlinear behavior through polynomial fitting. This model allows accurate distortion estimation from undersampled feedback signals by mathematically reconstructing the distortion characteristics without requiring high-frequency sampling, thus maintaining precision while reducing power consumption.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3C
AI summary
A amplifier system may include a predistorter receiving an input signal to generate a predistortion signal, a first converter receiving the predistortion signal to generate a preamplified signal, a power amplifier receiving the preamplified signal to generate an output signal based on the preamplified signal and the input signal, and a second converter sampling the output signal to generate a feedback signal. The power amplifier may produce a distortion signal at a first frequency, the second converter may sample the output signal using a timing signal with a second frequency that is lower than the first frequency to generate the feedback signal, and the predistorter, based upon the feedback signal, may predistort the predistortion signal to reduce the distortion signal at the first frequency.