Oscilloscope Noise Compensation for High-Speed Waveform Accuracy
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Solution Overview
Problem
Noise in oscilloscopes negatively impacts the accuracy of high-speed signaling waveform measurements, leading to inaccurate determinations of symbol error rate, SNDR, and TDECQ, particularly in applications like PCIE Gen6 and 400G Ethernet, causing devices to fail or pass incorrectly.
Innovation Solution
The oscilloscope characterizes its own noise waveform and uses this knowledge to compensate for noise in subsequent measurements by identifying spectral impulses and scaling the flat spectrum portion, converting back to the time domain to produce a noise-compensated waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If real-time oversampling is used to guarantee anti-aliasing, then measurement reliability is improved, but instrument noise impacts jitter and eye opening measurements causing measurement precision to deteriorate
Solution Approach 1:
The patent segments the measured waveform into signal components and noise components. By separating the deterministic signal from the random noise, the system can process each independently, allowing noise compensation without compromising the anti-aliasing properties of real-time oversampling
Solution Approach 2:
The patent creates a noise model by capturing and characterizing the oscilloscope's noise waveform separately. This noise copy is then subtracted from the measured signal, effectively removing the instrument noise impact while preserving the original signal integrity
2Measurement precision
If noise compensation is applied to improve measurement precision, then measurement accuracy is improved, but device complexity increases due to additional processing steps
Solution Approach 1:
The patent performs noise characterization in advance by capturing the oscilloscope's noise waveform when no signal is present. This preliminary noise model is stored and reused for subsequent measurements, avoiding the need for complex real-time noise analysis during actual signal measurement
Solution Approach 2:
The oscilloscope characterizes its own noise properties and uses this self-knowledge to compensate for its noise in subsequent measurements. The system serves itself by using its internal noise characteristics to improve its measurement accuracy without requiring external calibration equipment
3Measurement precision
If random noise is scaled for low BER measurements, then measurement sensitivity is improved, but measurement precision deteriorates due to noise conversion to jitter
Solution Approach 1:
The patent extracts the random noise component from the measured waveform and processes it separately. By taking out the noise before it can be converted to jitter through signal edges, the system prevents noise-induced measurement errors while maintaining sensitivity for low BER measurements
Data Source
AI summary
An oscilloscope includes one or more ports to connect to a device under test (DUT) and receive a signal, one or more analog-to-digital converter (ADC) to produce a waveform of digital samples of the signal, and one or more processors to: acquire and determine a measure of a noise waveform, acquire a waveform of a repeating pattern from the ADCs and determine its frequency spectrum, identify a spectral impulse portion of the frequency spectrum, determine a measure of a flat portion of the frequency spectrum, use the measure of the flat portion and the measure of the noise waveform to produce a noise compensation ratio, scale the flat portion with the noise compensation ratio and combine it with the spectral impulse portion of the frequency spectrum to produce a noise compensated frequency spectrum, convert the noise compensated frequency spectrum to a time domain waveform to measure performance of the DUT.