Dual RF Predistortion for Multiband IMD and Spectral Regrowth
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Solution Overview
Problem
High power RF amplifiers face significant challenges in suppressing intermodulation distortion (IMD) and spectral regrowth, particularly in multi-band scenarios, leading to increased complexity and cost in digital predistortion (DPD) systems, where existing techniques struggle to maintain low distortion in both in-band and out-of-band channels while achieving high operating efficiency.
Innovation Solution
A dual-predistorter system is employed, comprising a static predistorter to compensate for static nonlinearity and a dynamic predistorter to address memory and dynamic effects, with a low-speed feedback loop to train the dynamic predistorter, effectively suppressing IMD and spectral regrowth by generating the inverse of spurious distortion components, allowing for reduced sampling rates and lower modeling complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital predistortion is used to suppress intermodulation distortion in multi-band power amplifiers, then distortion suppression improves, but system complexity and cost increase
Solution Approach 1:
The DPD system is segmented into multiple independent predistorter modules, each designed to handle specific intermodulation distortion components (e.g., third-order, fifth-order IMD). This segmentation allows each module to focus on particular distortion mechanisms, reducing the overall complexity compared to a single comprehensive DPD system that would need to handle all distortion types simultaneously.
Solution Approach 2:
The patent extracts and addresses only the most significant distortion components (specifically third-order and fifth-order intermodulation products) rather than attempting to compensate for all possible nonlinearities. By taking out and treating only the dominant distortion mechanisms, the system achieves effective distortion suppression without the complexity of modeling and compensating for every nonlinear effect.
2Loss of energy
If high efficiency operation is achieved in the nonlinear region, then power efficiency improves, but spectral regrowth and distortion increase
Solution Approach 1:
The predistorters apply preliminary distortion compensation to the input signal before it enters the power amplifier. By pre-distorting the signal in the opposite direction of the expected nonlinear distortion, the system prepares the signal such that when it passes through the high-efficiency nonlinear amplifier region, the cumulative effect results in reduced spectral regrowth and distortion at the output.
Solution Approach 2:
The patent converts the harmful nonlinear effects of the power amplifier into a beneficial outcome by using the amplifier's inherent nonlinear characteristics to generate predictable distortion products, then using predistortion to cancel these products. The nonlinear region, which traditionally causes spectral regrowth, is transformed into an efficient operating mode when combined with the predistortion compensation.
3Productivity
If multiple bands are transmitted concurrently through parallel channels, then data throughput increases, but cost and design space increase
Solution Approach 1:
The patent merges multiple single-band predistorter designs into a unified multi-band predistortion system. Instead of implementing separate complete DPD systems for each band, the invention combines the predistorter modules to handle multiple bands concurrently through a single power amplifier, reducing the overall design space and component requirements while maintaining high data throughput.
Solution Approach 2:
The predistorter modules are designed with universal functionality to handle multiple frequency bands. Each predistorter module can be configured to address distortion in different bands, allowing the same hardware architecture to serve multiple bands simultaneously. This multi-functionality reduces the need for band-specific dedicated circuits, lowering cost and design complexity.
Data Source
AI summary
A digital predistorter comprising a first predistorter for generating out-of-band and inter-band distortion components for compensating for the static nonlinearity of a nonlinear element, and a second predistorter cascaded with the first predistorter, the second predistorter compensating for the in-band distortion of the nonlinear device wherein the cascade of the first predistorter and the second predistorter compensate for in-band, out-of-band and inter-band distortions when the cascade of the first, the second predistorter and the nonlinear element are driven with multiband signals.