Digital Post-Distortion Compensation for RF Receiver Non-Linearity
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Solution Overview
Problem
Radio-frequency receivers integrated into CMOS devices face non-linear signal distortion issues due to components like low noise amplifiers, mixers, and analog-to-digital converters, which impair the recovery and decoding of desired signals in the presence of undesired signals, leading to intermodulation and harmonic distortions that cannot be effectively removed by simple filtering.
Innovation Solution
A method involving the conversion of digitized RF signals into complex baseband signals, rotation to align with 0 Hz, calculation of compensation distortion components for pre-determined orders, and subtraction of these components from the rotated signal to obtain a compensated complex baseband signal, utilizing techniques like Hilbert filtering and frequency rotation to address non-linearity distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital signal processing is used to compensate for non-linear distortion, then signal linearity is improved, but computational complexity and power consumption increase
Solution Approach 1:
The patent segments the non-linear distortion compensation into multiple distinct digital signal processing stages: initial distortion compensation, intermodulation distortion removal, and harmonic distortion filtering. Each stage targets specific distortion components with optimized algorithms, preventing the need for a single high-power processing block while maintaining overall signal linearity.
Solution Approach 2:
The patent applies partial compensation by focusing digital signal processing efforts on the most problematic distortion components (intermodulation and harmonic distortions) rather than attempting to compensate for all non-linearities equally. This selective approach reduces computational load and power consumption while achieving sufficient signal quality for practical applications.
2Reliability
If filtering is used to remove harmonic distortion, then signal purity is improved, but desired signal components may be attenuated
Solution Approach 1:
The patent applies local quality by designing filters with frequency-selective characteristics that target specific distortion frequency components while preserving the desired signal band. The filtering operations are localized to specific frequency regions where distortion products appear, allowing aggressive filtering of unwanted components without affecting the integrity of the desired signal components.
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between the analog front-end and the baseband processing stages. This digital intermediary performs precise frequency-selective filtering and distortion compensation that is more selective and controllable than traditional analog filtering, enabling better rejection of distortion products while preserving desired signal components with minimal attenuation.
Data Source
AI summary
A method and apparatus to digitally remove in-band non-linear signal distortion caused by a radio frequency (RF)/intermediate frequency (IF) receiver circuit that has non-linearities, which are further affected by low-IF ADC sample aliasing.