RF Digital Predistortion Using Baseband-Derived Correction
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Solution Overview
Problem
Existing power amplifier linearization techniques, such as digital baseband predistortion, require wideband transmit paths and additional components like envelope detectors and RF delay lines, leading to increased cost, complexity, and inaccuracy, while RF envelope digital predistortion suffers from inaccuracy and loss.
Innovation Solution
A new predistortion system architecture that applies a predistortion function derived at baseband to the RF output, using a vector modulator and a digital delay to compensate for delay mismatch, reducing the need for wideband components and improving linearization by employing a lookup table or polynomial calculations for correction coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital baseband predistortion is implemented, then linearization performance is improved, but the transmit path bandwidth requirement increases significantly
Solution Approach 1:
The patent transitions from baseband predistortion to RF predistortion, changing the frequency dimension where predistortion is applied. By moving the predistortion operation from baseband to RF domain, the system achieves linearization without requiring the transmit path bandwidth to be expanded multiple times, thus resolving the bandwidth constraint while maintaining linearization performance
2Area of stationary object
If RF envelope digital predistortion is used, then transmit path bandwidth requirement is reduced, but system complexity and cost increase due to additional components
Solution Approach 1:
The patent extracts and removes the envelope detector and large RF delay line components from the RF envelope digital predistortion system. By eliminating these complex and costly components while retaining the essential predistortion function through alternative means, the system achieves the desired linearization with reduced complexity and cost
3Area of stationary object
If RF envelope digital predistortion is implemented, then transmit path bandwidth requirement is reduced, but measurement precision deteriorates due to additional components
Solution Approach 1:
The patent replaces complex, costly, and accuracy-limiting components (envelope detector and large RF delay lines) with simpler, more accurate digital processing methods. By using computationally efficient algorithms implemented in digital logic, the system achieves high linearization accuracy without the measurement errors introduced by analog components
Data Source
AI summary
A baseband-derived RF predistortion system using a lookup table having coefficients extracted at baseband and then applied at RF by means of a vector modulator. The architecture combines the narrowband advantage of envelope predistortion with the accuracy of baseband predistortion, and including compensation for memory effects. A polynomial-based alternative is also described.