Digital Predistortion Circuit for Cable TV Amplifier Non-Linearity
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Solution Overview
Problem
The transition to DOCSIS 3.1 standards in cable TV amplifiers results in non-linear operation, degrading signal quality and increasing power consumption, as the amplifiers operate in a higher peak-to-average power ratio, making it challenging to maintain advanced performance with improved signal quality and reduced power consumption.
Innovation Solution
A digital predistortion (DPD) system is implemented, comprising a non-linear datapath with parallel elements adding inverse non-linear components and a linear datapath to generate predistortion signals, which are combined to compensate for amplifier non-linearities, thereby improving signal quality and reducing power consumption by operating the amplifiers in a more efficient region.
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 due to non-linear operation
Solution Approach 1:
The patent applies digital predistortion by pre-processing the signal to add inverse non-linear characteristics before amplification. The DPD system calculates predistortion coefficients and applies them to the input signal, causing the amplifier's non-linear distortion to cancel out the predistortion, resulting in linear overall transmission. This preliminary action enables the amplifier to operate in non-linear region while maintaining signal quality and reducing power consumption.
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 implements predistortion by introducing opposite non-linear characteristics to counteract the amplifier's non-linear effects. The DPD system generates a predistortion signal with inverse amplitude-compression and phase-distortion characteristics that pre-compensate for the amplifier's non-linear behavior, ensuring the final output maintains high signal quality even when the amplifier operates in non-linear region.
Solution Approach 2:
The patent converts the harmful non-linear effects of the amplifier into beneficial cancellation effects. By deliberately adding inverse non-linear characteristics through predistortion, the amplifier's natural non-linearity becomes the mechanism that cancels the predistortion, resulting in linear overall transmission. This transforms the harmful non-linear distortion into a useful cancellation effect that enables power-efficient operation.
3Measurement precision
If multiple parallel datapath elements are added to compensate for different non-linear components, then compensation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the non-linear compensation task into multiple parallel datapath elements, each handling specific non-linear components. The system divides compensation into baseband path (amplitude and phase), video bandwidth path (amplitude), and harmonic paths (2nd and 3rd order harmonics). Each parallel path processes specific non-linear characteristics independently, improving compensation accuracy while maintaining manageable complexity through functional decomposition.
Data Source
AI summary
A digital predistortion (DPD) system includes an input configured to receive a DPD input signal. In some embodiments, a non-linear datapath is coupled to the input, where the non-linear datapath includes a plurality of parallel datapath elements each coupled to the input. By way of example, each of the plurality of parallel datapath elements is configured to add a different inverse non-linear component to the DPD input signal corresponding to a non-linear component of an amplifier. In various examples, a first combiner combines an output of each of the plurality of datapath elements to generate a first predistortion signal. In some embodiments, the DPD system further includes a linear datapath coupled to the input in parallel with the non-linear datapath to generate a second predistortion signal. In addition, a second combiner combines the first predistortion signal and the second predistortion signal to generate a DPD output signal.