Oscilloscope Cross-Correlation for Phase Noise Measurement
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Solution Overview
Problem
Oscilloscopes face limitations in accurately measuring signal characteristics like phase noise due to measurement errors introduced by input channels, which are difficult to distinguish from actual signal variations, especially when measuring RF signals, and are typically not suitable for data-type or spread-spectrum clocking signals beyond a limited frequency range.
Innovation Solution
A method using multiple channels of an oscilloscope with a digital signal processor to digitize signal copies, perform cross-correlation to separate signal variations from measurement errors, and extend the frequency range for phase noise measurements, allowing for accurate measurement of data and spread-spectrum clocking signals by removing SSC phase modulation and computing integrated phase jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional oscilloscope channels are used to measure signal characteristics, then the measurement process is simple and direct, but measurement precision deteriorates due to uncorrelated noise from multiple channels
Solution Approach 1:
The measurement process is segmented into multiple independent channel measurements followed by a correlation processing stage. Each channel measures the signal independently, and the results are combined through cross-correlation to eliminate uncorrelated noise components while preserving the actual signal characteristics.
Solution Approach 2:
Cross-correlation processing acts as an intermediary between multiple channel measurements and the final result. This intermediary process separates correlated signal components from uncorrelated noise, enabling precise measurement while using multiple channels.
2Measurement precision
If spectrum analyzers are used to measure phase noise, then measurement precision improves for RF signals, but adaptability deteriorates as they cannot measure data-type or spread-spectrum clocking signals
Solution Approach 1:
The oscilloscope measurement system is enhanced to perform multiple functions: it can measure traditional RF signals, data-type signals, and spread-spectrum clocking signals with equal precision. The cross-correlation technique provides a universal measurement approach that adapts to different signal types without requiring separate specialized instruments.
Solution Approach 2:
The measurement approach changes parameters such as measurement bandwidth, sampling rate, and correlation processing parameters based on the signal type being measured. This enables the same base instrument to accurately measure diverse signal types including RF, data, and spread-spectrum clocking signals.
3Measurement precision
If dedicated phase noise measurement systems are used, then measurement precision improves with low error floor, but adaptability deteriorates by being limited to maximum offset frequency of 100 MHz
Solution Approach 1:
The measurement system dynamically adjusts its operating parameters including frequency range, bandwidth, and sampling rate based on the measurement requirements. This dynamic adaptability allows the oscilloscope-based system to achieve high precision measurements across a wide frequency range far exceeding the 100 MHz limitation of dedicated systems.
Solution Approach 2:
The system changes measurement parameters such as offset frequency range, resolution bandwidth, and sweep time to optimize measurements across different frequency ranges. This enables precise phase noise measurement from low frequencies up to several GHz, breaking the 100 MHz barrier of dedicated instruments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the sensitivity and accuracy of measurements by isolating signal variations correlated across channels, reducing uncorrelated noise, and extending the frequency range for phase noise measurements, effectively addressing the limitations of conventional oscilloscopes.
Implementation Method 1
A method using multiple channels of an oscilloscope with a digital signal processor to digitize signal copies, perform cross-correlation to separate signal variations from measurement errors
Data Source
AI summary
A method and system measure a characteristic of a signal under test (SUT) using a signal measurement device. The method includes receiving and digitizing the first and second copies of the SUT through first and second input channels to obtain first and second digitized waveforms; repeatedly determining measurement values of the SUT characteristic in the first and second digitized waveforms to obtain first and second measurement values, which are paired in measurement value pairs; multiplying the first and second measurement values in each of the measurement value pairs to obtain measurement products; determining an average value of the measurement products to obtain an MSV of the measured SUT characteristic; and determine a square root of the MSV to obtain an RMS value of the measured SUT characteristic. The RMS value substantially omits variations not in the SUT, which are introduced by only one of the first and second input channels.