Frequency-Shaped DPD for Band-Limited Power Amplifiers
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Solution Overview
Problem
Digital predistortion (DPD) circuits face challenges in effectively compensating for nonlinearities in power amplifiers due to bandwidth limitations, leading to attenuated predistortion signals and increased distortion, especially when using band-limited components.
Innovation Solution
Implementing frequency-shaped DPD, which trains the DPD actuator circuit to operate within a limited bandwidth by generating frequency-shaped DPD parameters and feedback signals, excluding out-of-band predistortion terms, and using uptilt filters to counteract frequency-dependent attenuation in transmission media like coaxial cables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If band-limited components are used in DPD circuits, then device complexity is reduced, but predistortion signal is attenuated and distortion increases
Solution Approach 1:
The patent applies frequency-shaped predistortion parameters that are specifically designed to match the bandwidth characteristics of band-limited components. By changing the parameter of predistortion signals to be frequency-shaped rather than wideband, the system achieves effective predistortion with band-limited components while minimizing distortion.
Solution Approach 2:
The patent implements predistortion only within the limited bandwidth of the components rather than attempting full wideband predistortion. This partial action approach focuses predistortion energy where it is most effective (within the passband) and avoids the need for expensive wideband components, thereby reducing device complexity while maintaining acceptable performance.
2Object-generated harmful factors
If wideband DPD is implemented, then distortion compensation is improved, but device complexity and cost increase due to wideband components
Solution Approach 1:
The patent changes the parameter of predistortion signals from wideband to frequency-shaped with limited bandwidth. This allows effective distortion compensation within the operational bandwidth without requiring wideband components, thereby reducing device complexity and cost while maintaining good distortion compensation performance within the passband.
Solution Approach 2:
Instead of implementing full wideband predistortion, the patent applies predistortion partially within the limited bandwidth of band-limited components. This partial predistortion approach achieves sufficient distortion compensation for the signal band of interest without the need for expensive wideband components across the entire possible frequency range.
3Measurement precision
If frequency-shaped DPD is implemented with band-limited components, then low-frequency performance is improved, but out-of-band predistortion terms are excluded
Solution Approach 1:
The patent extracts and removes out-of-band predistortion terms from the predistortion signal, keeping only the in-band terms that are relevant to the signal frequency range. This extraction of necessary components improves low-frequency performance by focusing predistortion energy where it is needed, while the excluded out-of-band terms do not provide additional benefit and may even cause harm.
Solution Approach 2:
The patent changes the frequency distribution parameter of predistortion signals to be concentrated in the in-band region rather than spread across wide bandwidth. This frequency-shaping parameter change enhances low-frequency and in-band performance by allocating predistortion resources efficiently to where they are most effective.
Data Source
AI summary
Various examples are directed to a digital predistortion (DPD) circuit comprising a DPD actuator circuit, a DPD feedback frequency-shaping filter, a basis matrix generator circuit, a basis matrix frequency-shaping filter, and a DPD adaption circuit. The DPD actuator circuit may generate a predistorted signal based at least in part on an input signal and a set of frequency-shaped DPD parameters. The DPD feedback frequency-shaping filter may filter a DPD feedback signal to generate a frequency-shaped DPD feedback signal. A passband of the DPD feedback frequency-shaping filter may include substantially all of a bandwidth of the input signal and exclude a distortion term outside the bandwidth of the input signal. The basis matrix generator may generate a basis matrix based at least in part on a power amplifier feedback signal The basis matrix frequency-shaping filter may generate a frequency-shaped basis matrix based at least in part on the basis matrix. The DPD adaption circuit may be configured to generate the set of frequency-shaped DPD parameters based at least in part on the frequency-shaped basis matrix and the frequency-shaped DPD feedback signal.