Digital PLL Spur Suppression Using Linear Prediction Filtering
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Solution Overview
Problem
Digital phase-locked loops generate spurious energy due to coupling mechanisms like time-to-digital converter gain error and non-linearity, leading to undesirable periodic tones in output clock signals, which can cause mixing of unwanted signals, emission mask violations, and increased jitter.
Innovation Solution
A linear prediction technique is employed to determine the location of spurious content and suppress it using an all-zero filter with weights corresponding to the zeros of the filter at frequencies of spurs, implemented in a digital phase-locked loop, which adapts to different configurations and environmental changes without requiring a priori configuration or increasing the noise floor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional digital phase-locked loop components are used, then the basic clock signal generation function is achieved, but spurious energy and periodic tones are introduced into the output
Solution Approach 1:
The patent uses linear prediction to model the spurious energy components and then applies an all-zero filter with zeros placed at the spur frequencies to cancel them out. This converts the harmful spurious energy into a predictable pattern that can be systematically eliminated through mathematical filtering, improving output signal quality without sacrificing basic clock generation functionality.
2Object-generated harmful factors
If filtering techniques are applied to suppress spurs, then spurious energy is reduced, but device complexity increases
Solution Approach 1:
The patent changes the parameters of the filter by placing zeros at specific frequencies corresponding to the spur locations in the frequency domain. By adjusting the zero locations based on the predicted spur frequencies, the filter effectively suppresses spurious energy without requiring a complex filter structure, maintaining simplicity while achieving suppression.
3Object-generated harmful factors
If traditional spur suppression methods are used, then some spurs are reduced, but multiple spurs cannot be suppressed simultaneously
Solution Approach 1:
The all-zero filter designed with multiple zeros can simultaneously suppress multiple spurs at different frequencies in a single filtering operation. This multi-functional approach eliminates the need for separate filtering stages for each spur, improving productivity by suppressing multiple spurious components concurrently while maintaining a unified filter structure.
4Adaptability or versatility
If adaptive techniques are implemented to handle environmental changes, then suppression effectiveness is maintained, but device complexity increases
Solution Approach 1:
The patent employs linear prediction to continuously monitor and model the spurious energy components in the output signal. By using feedback from the predicted spur locations to adjust the zero placements in the all-zero filter, the system adapts to environmental changes and frequency drifts automatically, maintaining suppression effectiveness without requiring manual reconfiguration or complex adaptive mechanisms.
Data Source
AI summary
A technique uses linear prediction to determine the location of spurious content in a digital phase-locked loop and suppresses the spurious content from propagating to the clock output. In at least one embodiment, the technique implements an iterative (e.g., recursive) computation.