CATV Amplifier Predistortion Circuit for Mirror Image Compensation
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Solution Overview
Problem
The transition to DOCSIS 3.1 standards in cable TV amplifiers requires higher signal quality and reduced power consumption, but existing digital predistortion methods struggle to compensate for non-linear effects, especially baseband non-linear mirror image components, which degrade signal quality and fail to meet high modulation error ratio specifications.
Innovation Solution
A digital predistortion system that includes multiple non-linear datapaths and a conjugation block to model and compensate for both baseband and harmonic non-linear components, including mirror image components, within a digital front-end chip, to generate a predistortion signal that corrects for these effects before amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DOCSIS 3.1 standards are implemented with higher data rates and sophisticated functions, then data transmission capability is improved, but power consumption of CATV amplifiers increases
Solution Approach 1:
The patent applies preliminary action by implementing digital predistortion that pre-compensates for non-linear effects before the signal enters the power-consuming CATV amplifier. The predistortion signal is generated in advance to counteract the amplifier's non-linear behavior, allowing the amplifier to operate more efficiently and reducing overall power consumption while maintaining high data rate transmission capabilities required by DOCSIS 3.1
2Use of energy by moving object
If CATV amplifiers operate in non-linear region to reduce power consumption, then power efficiency is improved, but signal quality deteriorates due to non-linear effects
Solution Approach 1:
The patent applies preliminary anti-action by generating a predistortion signal that pre-counteracts the non-linear effects of the CATV amplifier. The predistortion process introduces opposite non-linearities before amplification, so that when the signal passes through the amplifier operating in non-linear region, the combined effect linearizes the overall transmission, maintaining signal quality and modulation error ratio specifications while enabling power-efficient amplifier operation
Solution Approach 2:
The patent implements feedback by using a feedback path that captures the output signal from the CATV amplifier and feeds it back through a feedback processor. This feedback mechanism allows the system to continuously monitor and adapt to the amplifier's non-linear characteristics, adjusting the predistortion signal in real-time to maintain optimal signal quality despite the amplifier operating in non-linear region for improved power efficiency
3Device complexity
If existing digital predistortion methods are used, then implementation simplicity is maintained, but compensation accuracy for non-linear effects including mirror image components is insufficient
Solution Approach 1:
The patent applies segmentation by dividing the predistortion process into multiple independent datapaths, each targeting specific non-linear components. The system segments the non-linear compensation into: (1) main non-linear components path, (2) mirror image non-linear components path with conjugation block, and (3) linear components path. This segmentation allows each path to be optimized for its specific function while maintaining overall implementation feasibility and improving compensation accuracy for all non-linear effects including mirror image components
Data Source
AI summary
A digital predistortion (DPD) system includes an input configured to receive a DPD input signal. In some examples, a non-linear datapath is coupled to the input, where the non-linear datapath is configured to add a non-linear mirror image component to the DPD input signal to provide a non-linear signal that is used to generate a first predistortion signal. In some embodiments, a linear datapath is coupled to the input in parallel with the non-linear datapath to generate a second predistortion signal. A first combiner is configured to combine the first predistortion signal and the second predistortion signal to generate a DPD output signal.