Spur Cancellation Circuit for Precise PLL Tone Detection
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Solution Overview
Problem
Existing measurement techniques fail to accurately identify and quantify spurious tones in signals generated by phase-locked loops and other timing circuits, which are crucial for ensuring that components do not produce significant spurious tones at frequencies of interest.
Innovation Solution
A device equipped with a phase-locked loop (PLL) and a spur cancellation circuit that uses a frequency control word to generate a second signal, allowing the cancellation of spurious tones and determining their magnitude by correlating sine and cosine terms against a sense node, with the resulting error signals adjusting the cancellation signal to eliminate or reduce the spurious tone in the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement techniques are used to detect spurious tones, then the measurement process is simple, but the measurement precision is insufficient to accurately identify and quantify spurious tones
Solution Approach 1:
A spur cancellation circuit is introduced as an intermediary component between the signal source and measurement equipment. This circuit actively cancels spurious tones by generating anti-phase signals, enabling accurate measurement of spurious tone magnitudes that would otherwise be impossible to detect with conventional techniques
Solution Approach 2:
The patent replaces conventional passive measurement approaches with an active electronic cancellation system. Instead of attempting to measure spurious tones directly through passive filtering or averaging, the system uses active signal processing with sine and cosine term correlation to eliminate spurs and measure their magnitudes accurately
2Measurement precision
If a spur cancellation circuit is implemented to accurately measure spurious tones, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The spur cancellation function is divided into separate modular components: a spur cancellation circuit with sine and cosine term generators, a correlation unit, and a measurement output stage. This segmentation allows the complex measurement function to be implemented through manageable, independent modules that can be configured for different measurement needs
Data Source
AI summary
A spur measurement system uses a first device with a spur cancellation circuit that cancel spurs responsive to a frequency control word identifying a spurious tone of interest. A device under test generates a clock signal and supplies the clock signal to the first device through an optional divider. The spur cancellation circuit in the first device generates sine and cosine weights at the spurious tone of interest as part of the spur cancellation process. A first magnitude of the spurious tone in a phase-locked loop in the first device is determined according to the sine and cosine weights and a second magnitude of the spurious tone in the clock signal is determined by the first magnitude divided by gains associated with the first device.