Amplifier Predistortion Using Dual Out-Band Feedback
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Solution Overview
Problem
Existing amplifier systems face sub-optimal performance due to the separate processing of out-bands from either side of the in-band PA output in digital predistortion methods, leading to imbalance and deterioration of adjacent channel leakage ratio (ACLR) performance.
Innovation Solution
An amplifier configuration that includes in-band and out-band extraction units to process both the in-band and out-bands of the PA output simultaneously, using a signal processing unit to adjust predistortion coefficients based on information from both sides, thereby improving linearity and balancing ACLR performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If out-bands from either side of the in-band PA output are processed separately for evaluation of DPD model, then the distortion in the selected side is corrected, but the performance of the non-selected side deteriorates leading to ACLR imbalance
Solution Approach 1:
The patent combines the processing of both low frequency side out-bands and high frequency side out-bands into a single unified DPD model evaluation process. Instead of selecting only one side for processing, the system extracts and processes out-bands from both sides simultaneously, merging the information from both sides to optimize the DPD model coefficients. This resolves the contradiction by ensuring that distortion correction benefits are distributed to both sides, preventing ACLR imbalance while maintaining correction accuracy.
2Device complexity
If bandpass filter is placed in feedback loop to reduce ADC sampling rate, then the ADC cost is reduced, but a significant amount of information in out-bands is thrown out resulting in sub-optimal performance
Solution Approach 1:
The patent extracts out-band information from the PA output using dedicated extraction units that specifically target and extract the out-band frequency components. Rather than using a bandpass filter that would block out-bands, the system extracts the out-band information that would otherwise be discarded. This extracted out-band information is then fed into the DPD model evaluation process, allowing the system to maintain low ADC sampling rates while preserving and utilizing the previously lost out-band information for improved linearity correction.
Data Source
AI summary
An in-band extraction unit is configured to extract an in-band from an output signal. An out-band extraction unit is configured to extract at least one pair of out-bands including a low frequency side out-band and a high frequency side out-band from the output signal. An ADC is configured to convert the extracted in-band and out-bands to digital signals. A signal processing unit is configured to process information included in the digital signals converted by the analog to digital converter and adjust an operation of predistorting an input baseband digital signal to generate the output signal.