Oscilloscope Noise Reduction via Spectral Subtraction
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Solution Overview
Problem
Real-time oscilloscopes face challenges in accurately measuring noise levels due to their own noise interference, which can lead to incorrect compliance assessments in industry protocols, especially as measured noise levels decrease, and current methods for noise removal are cumbersome or ineffective for non-scalar noise representations.
Innovation Solution
The oscilloscope system performs Fourier transforms on measured radio frequency signals to compute new spectra, then applies inverse Fourier transforms to reduce noise, allowing for noise removal from waveforms without requiring physical channel splitting, thus improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If oscilloscope noise is removed by direct subtraction from scalar measurements, then measurement precision is improved, but the method is only applicable to scalar representations and not to general waveform data such as histograms, frequency spectra, time trends, and eye diagrams
Solution Approach 1:
The patent transforms noise removal from a scalar subtraction operation to a spectrum-domain operation. By converting waveforms to frequency spectra via Fourier transform, the patent enables noise removal across multiple representation types (time domain, frequency domain, histograms) through unified spectral manipulation, resolving the limitation of scalar-only applicability
Solution Approach 2:
The patent introduces frequency spectrum as an intermediary representation between the original waveform and the final noise-removed waveform. This spectral domain serves as a universal intermediate form that can represent various noise types (random jitter, systematic jitter, voltage noise) regardless of their original representation, enabling consistent noise removal across different measurement types
2Measurement precision
If oscilloscope noise is removed by converting voltage noise to jitter using slew rate measurement, then jitter measurement precision is improved, but the method requires measuring change of voltage over time and assumes uncorrelated noise between oscilloscope and DUT
Solution Approach 1:
The patent extracts oscilloscope noise from the total measured noise by operating in the frequency spectrum domain. Through spectral subtraction, the oscilloscope's contribution to noise is separated and removed, leaving only the DUT's noise characteristics. This extraction method eliminates the need for slew rate measurements and uncorrelated noise assumptions, simplifying the measurement process while maintaining precision
3Measurement precision
If physical channel splitting is used to remove oscilloscope noise from jitter trend data, then noise removal is achieved, but the process is cumbersome and may introduce errors due to cable mismatches and non-ideal connectors
Solution Approach 1:
The patent replaces the mechanical/physical channel splitting method with a computational approach using Fourier transforms and spectral subtraction. Instead of physically separating signals through multiple channels and cables, the patent uses digital signal processing to remove oscilloscope noise from the spectrum, eliminating cable mismatch errors and connector issues while maintaining noise removal effectiveness
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 method effectively lowers the noise floor of the oscilloscope and enhances measurement accuracy by isolating and subtracting oscilloscope noise from the measured signals, while preserving the noise from the device under test, facilitating compliance with industry standards.
Implementation Method 1
perform a first Fourier transform to compute a first new spectrum based on the measurement of the first radio frequency signal
Implementation Method 2
compute a first waveform of the first new spectrum with noise of the oscilloscope reduced by performing a first inverse Fourier transform based on the first new spectrum
Data Source
AI summary
An oscilloscope includes a memory that stores instructions; and a processor that executes the instructions. When executed by the processor, the instructions cause the oscilloscope to obtain a measurement of a first radio frequency signal; perform a first Fourier transform to compute a first new spectrum based on the measurement of the first radio frequency signal; and compute a first waveform of the first new spectrum with noise of the oscilloscope reduced by performing a first inverse Fourier transform based on the first new spectrum.