Drain-Current Predistorter for RF Amplifier Memory Compensation
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Solution Overview
Problem
Conventional predistortion schemes fail to accurately compensate for memory effects caused by variations in drain voltage in RF power amplifiers, leading to non-symmetrical spectra and inefficiencies, especially in highly efficient amplifiers like Doherty amplifiers.
Innovation Solution
A predistorter that estimates the drain current using a linear filter and generates signal components based on gain functions representing the sensitivity of the amplifier, effectively combining these components to form an output signal that compensates for frequency memory effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional predistortion schemes are used, then distortion is reduced, but memory effects caused by drain voltage variations are not compensated, leading to non-symmetrical spectra
Solution Approach 1:
The predistorter segments the drain current estimation into multiple components: a linear filtered component and nonlinear components derived from gain functions. This segmentation allows independent optimization of each component to address different aspects of memory effects while maintaining spectral symmetry
Solution Approach 2:
The predistorter implements feedback by using the estimated drain current (derived from output signal measurements) to dynamically adjust the predistortion signal. This closed-loop approach enables continuous compensation of memory effects, ensuring accurate spectral symmetry maintenance under varying operating conditions
2Loss of energy
If highly efficient amplifiers like Doherty amplifiers are used, then efficiency at backoff is improved, but memory effects become more pronounced due to fundamental drain voltage variations
Solution Approach 1:
The predistorter performs preliminary action by pre-compensating for the expected memory effects before the signal enters the power amplifier. By estimating the drain current variations that will occur in the Doherty amplifier and applying counteracting predistortion, the system prevents memory effects from manifesting, thereby maintaining both efficiency and spectral symmetry
Solution Approach 2:
The predistorter dynamically changes parameters (gain functions) based on the estimated drain current amplitude. These parameter adjustments allow the predistortion mechanism to adapt to the varying operating conditions of the Doherty amplifier, effectively compensating for memory effects across different power levels while maintaining high efficiency
3Adaptability or versatility
If the predistorter uses gain functions representing amplifier sensitivity, then tracking capabilities and dynamic non-linearity correction are enhanced, but device complexity increases
Solution Approach 1:
The predistorter uses copying by creating simplified models (gain functions) that replicate the essential characteristics of the complex power amplifier behavior. Instead of directly modeling the full nonlinear dynamics, the system uses scaled versions of the drain current estimate passed through gain functions, reducing computational complexity while maintaining accurate tracking of memory effects
Data Source
AI summary
The present invention relates to a predistorter for reducing memory effects in RF power amplifiers. The invention also relates to a method for reducing memory effects in RF power amplifiers and to a base station including such a predistorter. A predistorter according to the invention includes first means (1) for generating a first signal component, which is an estimate of a drain current of said amplifier, which means (1) for generating said first signal component comprises a linear filter, second means (8) for generating a second signal component as a function of said first signal component and at least one first gain function; third means (9) for generating a third signal component as a function of a conjugate of said first signal component and at least one second gain function, and fourth means (7) for combining at least said second signal component and said third signal component to form an output signal. The output signal from the predistorter is further used as input to the power amplifier, which when amplified reduces the memory effects of the amplifier.