Digital Pre-Distortion for RF Amplifier Non-Linearity
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Solution Overview
Problem
Digital radio transmission systems face challenges with high peak-to-average power ratios due to non-linear responses in power amplifiers, leading to out-of-band spurious signals and harmonics, which existing methods struggle to effectively compensate for without detailed knowledge of the transmitted signal.
Innovation Solution
A compensation apparatus that digitizes both the RF input and feedback from the power amplifier, calculates dynamic pre-distortion coefficients, and applies a digital pre-distortion filter to reduce peak power, allowing for efficient operation of the power amplifier without requiring prior knowledge of the symbols being transmitted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital pre-distortion with fixed tables is used to compensate for gain compression, then distortion effects are reduced, but the system requires detailed knowledge of the transmitted signal and cannot handle high peak-to-average power ratios effectively
Solution Approach 1:
The patent transitions from static fixed pre-distortion tables to dynamic adaptive pre-distortion coefficients. The system continuously calculates and updates pre-distortion coefficients based on real-time feedback from the power amplifier output, allowing the compensation to adapt to varying signal conditions, modulation schemes, and amplifier operating points without requiring prior knowledge of the transmitted signal content.
Solution Approach 2:
The patent implements a feedback mechanism where the output of the power amplifier is fed back to a detector that measures the actual output signal characteristics. This feedback information is used to calculate updated pre-distortion coefficients, creating a closed-loop system that continuously optimizes distortion compensation based on actual amplifier behavior rather than relying on predetermined tables.
2Manufacturing precision
If analog pre-distortion with diodes is used to generate power transition points, then gain compression effects are offset, but the system complexity increases and adaptability to different modulation schemes is limited
Solution Approach 1:
The patent replaces complex analog pre-distortion circuitry with digital signal processing. Instead of using analog diodes and circuits to generate pre-distortion waveforms, the system uses digital algorithms to calculate and apply pre-distortion coefficients, significantly reducing analog circuit complexity while maintaining or improving distortion compensation accuracy.
Solution Approach 2:
The patent changes the operating parameters of the power amplifier by dynamically adjusting the pre-distortion coefficients based on the actual output power and signal characteristics. This allows the system to optimize the amplifier's operating point in real-time, improving gain linearity across different power levels and modulation schemes without requiring complex fixed analog circuits for each scenario.
3Loss of energy
If peak power reduction methods are used to counteract high peak-to-average power levels, then amplifier efficiency improves, but the methods require detailed knowledge of the actual transmitted signal
Solution Approach 1:
The patent uses feedback from the amplifier output to determine the actual signal characteristics and power levels. This feedback information enables the system to apply appropriate peak power reduction techniques dynamically, improving amplifier efficiency without requiring prior knowledge of the transmitted signal content, as the system adapts based on measured output characteristics.
Solution Approach 2:
The patent applies pre-distortion to the input signal before amplification, which preliminarily shapes the signal to anticipate and compensate for amplifier non-linearities and peak power issues. This preliminary action reduces the peak-to-average power ratio at the amplifier input, allowing more efficient operation without requiring detailed knowledge of the eventual transmitted signal content.
Data Source
AI summary
An analog radio frequency input and an analog feedback from an output of a radio frequency amplifier are digitized and down-converted. Pre-distortion coefficients are calculated based on the down-converted input and down-converted feedback and the down-converted input is filtered using the pre-distortion coefficients. The filter output is then up-converted to a carrier frequency and converted to analog to be provided to the radio frequency amplifier.