Adaptive Spur Cancellation with Frequency Tracking in PLLs
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Solution Overview
Problem
Existing spur cancellation systems in phase-locked loops and timing circuits fail to accurately track and cancel spurious tones, especially when the spur frequency changes, leading to reduced cancellation quality, especially in applications with multiple spurs or asynchronous inputs.
Innovation Solution
An adaptive spur frequency tracking method that extracts phase information from spur cancellation signals to update the target spur frequency, using a frequency tracking circuit to adjust the frequency control word based on phase changes, ensuring accurate cancellation of spurious tones by correlating sine and cosine terms and applying negative feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed frequency spur cancellation signal is used, then the cancellation is simple to implement, but the cancellation quality deteriorates when spur frequency changes
Solution Approach 1:
The patent implements a frequency tracking circuit that dynamically adjusts the spur cancellation signal frequency based on detected phase changes. Instead of using a fixed frequency signal, the system continuously updates the frequency control word to match the actual spur frequency, thereby maintaining high cancellation quality while adapting to frequency variations.
Solution Approach 2:
The patent employs a feedback mechanism where the phase of the spur cancellation signal is monitored and used to update the frequency control word. This closed-loop feedback ensures that the cancellation signal remains synchronized with the spur frequency, resolving the contradiction between implementation simplicity and cancellation quality under varying conditions.
2Measurement precision
If adaptive frequency tracking is implemented, then the cancellation quality improves under frequency changes, but the system complexity increases
Solution Approach 1:
The frequency tracking circuit performs multiple functions: it detects phase changes, calculates frequency deviations, and updates the frequency control word. By consolidating these functions into a single integrated circuit, the patent minimizes the increase in system complexity while achieving adaptive frequency tracking and maintaining high cancellation quality.
3Measurement precision
If phase information extraction is used for frequency tracking, then the spur cancellation accuracy improves, but the processing complexity increases
Solution Approach 1:
The patent replaces complex mechanical or analog frequency detection methods with digital phase information extraction and processing. By using digital signal processing techniques to extract phase information and update the frequency control word, the system achieves high spur cancellation accuracy while keeping the processing implementation straightforward and integrated.
Data Source
AI summary
A spur cancellation circuit receives a target spur frequency indicative of a frequency of a spur to be canceled and supplies a spur cancellation signal based on the frequency. A frequency tracking circuit tracks a change in the frequency of the spur to be canceled based on a change in phase of the spur cancellation signal and generates an updated target spur frequency based on the change in the frequency of the spur.