Digital Pre-Distortion for DAC Harmonic and Image Signal Cancellation
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Solution Overview
Problem
Digital-to-analog converters (DACs) introduce non-linear distortions such as harmonic and image signals due to parasitic effects, which are difficult to address and can compromise signal quality in digital media cable communications, especially as the number of channels increases, leading to less stringent interoperability standards.
Innovation Solution
A pre-distortion system that generates and applies correction signals to the input signal to cancel or attenuate harmonic and image distortions before digital-to-analog conversion, using signal generators, controllers, and correction modules to select and apply distortion correction coefficients based on the input signal type and characteristics of the DAC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If digital signals are processed through conventional mixing and up-conversion before DAC conversion, then data transmission capability is maintained, but non-linear distortions (harmonic and image signals) are introduced by the DAC
Solution Approach 1:
The patent applies pre-distortion processing to the digital signal before it enters the DAC. This preliminary action introduces opposite distortions that will cancel out the non-linear distortions generated by the DAC during conversion, thereby maintaining data transmission capability while eliminating harmful harmonic and image signals
Solution Approach 2:
The pre-distortion system generates correction signals with opposite polarity and characteristics to the expected DAC distortions. These anti-actions are applied to the input signal, creating a predistorted signal that, when processed by the DAC, results in cancellation of the harmful non-linear effects
2Productivity
If the number of channels is increased to improve communication capacity, then data throughput is enhanced, but the stringency of emission standards becomes less enforceable and distortion effects increase
Solution Approach 1:
By applying pre-distortion processing to each channel before DAC conversion, the system maintains high communication capacity with multiple channels while proactively eliminating the distortion effects that would otherwise accumulate and degrade signal quality across the expanded channel set
3Manufacturing precision
If equalizers are used at the receiver to attenuate linear distortions, then linear distortion effects are reduced, but non-linear distortions remain difficult to address
Solution Approach 1:
Instead of attempting to correct non-linear distortions at the receiver, the patent applies pre-distortion at the transmitter to proactively eliminate harmonic and image signals before they are generated by the DAC. This preliminary correction makes non-linear distortion management as effective as linear distortion attenuation
Solution Approach 2:
The patent converts the harmful non-linear distortion characteristics of the DAC into a benefit by characterizing these distortions and applying opposite pre-distortion. The harmful parasitic effects are measured and then used to generate correction signals that cancel the distortions, turning the DAC's non-linearity from a problem into a solvable parameter
Data Source
AI summary
A pre-distortion circuit that may introduce a pre-distortion signal in a communication channel by determining a harmonic signal of the signal to be output. One or more image correction signals of the signal to be output may be determined. The one or more image correction signals may be complex conjugate signal variations of the signal to be output. The harmonic signal, the one or more image correction signals and the signal to be output may be combined into a combined output signal. The combined output signal may be transmitted to a digital-to-analog converter. The predistortion circuit may be implemented in a FPGA, an ASIC, a digital-to-analog converter, and/or a separate IC package.