Spur Cancellation Circuit Using PLL Correlation for Spur Magnitude Measurement
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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 programmable frequency control word to generate and cancel spurious tones, determining their magnitude by correlating sine and cosine terms against a sense node, and storing weights for subsequent calculation of spur amplitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing measurement techniques are used, then the measurement process is simple, but the accuracy of identifying spurious tones is insufficient
Solution Approach 1:
The patent introduces a spur cancellation circuit 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 spurs that would otherwise be impossible to detect with conventional techniques. The intermediary circuit bridges the gap between simple measurement and high precision requirements.
Solution Approach 2:
The spur cancellation circuit performs preliminary anti-action by pre-canceling spurious tones before they reach the measurement equipment. By generating cancellation signals in advance that are opposite in phase to the expected spurs, the system eliminates the harmful spurious tones proactively, allowing subsequent measurement of their original magnitudes through the cancellation depth.
2Measurement precision
If a phase-locked loop with spur cancellation circuit is used, then spurious tones can be accurately measured, but the device complexity increases
Solution Approach 1:
The PLL circuit serves multiple functions: it generates the test signal, provides frequency control through programmable dividers, and works in conjunction with the spur cancellation circuit to enable both signal generation and spur measurement. This multi-functionality reduces the need for separate dedicated components, managing complexity while achieving precise spur magnitude determination.
Solution Approach 2:
The spur cancellation circuit employs feedback mechanisms where the cancellation signals are continuously adjusted based on the detected spur characteristics. The circuit monitors the output and dynamically modifies the cancellation signal parameters to maintain optimal spur suppression, enabling accurate measurement through the feedback-controlled cancellation process.
3Adaptability or versatility
If programmable frequency control words are used to identify spurious tones, then flexibility in measuring different frequencies is improved, but the complexity of frequency control increases
Solution Approach 1:
The frequency control mechanism uses programmable dividers that can be dynamically reconfigured through frequency control words. This allows the system to adapt to different measurement frequencies by changing the divider ratios programmatically, providing versatility without requiring multiple fixed-frequency circuits. The dynamic reconfiguration capability enables flexible measurement across a range of frequencies.
Solution Approach 2:
The system changes the frequency parameter dynamically by loading different frequency control words into the programmable divider. This parameter change mechanism allows the same hardware circuit to measure spurious tones at various frequencies by simply updating the control word values, achieving adaptability through software-controlled parameter modification rather than hardware changes.
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.