DPD Feedback Filtering for Wideband RF Amplifiers at Lower Sampling Rates
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Solution Overview
Problem
Current digital predistortion (DPD) systems face challenges in increasing bandwidth without significantly increasing complexity and cost, particularly in multi-channel wideband wireless transmitters, leading to inefficiencies and higher power consumption.
Innovation Solution
The implementation of a DPD feedback signal with a narrow band-pass filter in the feedback path, allowing for extended bandwidth without modifying digital signal processing components, and utilizing direct learning algorithms to reduce the need for digital FIR filters and multi-pole ceramic filters, thereby decreasing the number of multipliers and simplifying the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the DPD processing speed is increased to meet higher instantaneous bandwidth requirements, then the bandwidth capability is improved, but the system cost and power consumption increase due to higher sampling rates in FPGAs, DACs, and ADCs
Solution Approach 1:
The patent segments the DPD processing function into two distinct parts: a low-speed DPD processor that handles the main predistortion computation, and a separate feedback path that captures and processes only the relevant feedback signals. This segmentation allows the expensive high-speed components to be eliminated while maintaining the required bandwidth capability through the low-speed processed feedback path.
2Speed
If the instantaneous bandwidth is increased, then the bandwidth capability is improved, but the memory effects increase causing the DPD algorithm to become much more complex and take longer to design, optimize and test
Solution Approach 1:
The patent extracts and removes the memory effects from the DPD algorithm by using the captured feedback signal to directly compensate for nonlinearities and memory effects. Instead of modeling complex memory effects within the DPD algorithm itself, the system captures the actual feedback signal containing all distortion components and uses it to generate the compensation signal, thereby eliminating the need for complex memory effect modeling.
3Speed
If conventional DPD systems use wide bandwidth processing, then the bandwidth capability is improved, but the system complexity and cost increase due to requirements for high sampling rates and stringent RF/IF filter specifications
Solution Approach 1:
The patent introduces an intermediary feedback capture mechanism that sits between the power amplifier output and the DPD processor input. This intermediary captures the feedback signal and processes it at low speed, acting as a mediator that allows the high-bandwidth system to operate with low-speed processing components. The feedback capture mechanism translates the high-frequency signal information into a form that can be processed slowly, eliminating the need for expensive high-speed components and stringent filter requirements.
Data Source
AI summary
A digital predistortion linearization method is provided for increasing the instantaneous or operational bandwidth for RF power amplifiers employed in wideband communication systems. Embodiments of the present invention provide a method of increasing DPD linearization bandwidth using a feedback filter integrated into existing digital platforms for multi-channel wideband wireless transmitters. An embodiment of the present invention utilizes a DPD feedback signal in conjunction with a low power band-pass filter in the DPD feedback path.