Digital Oscilloscope Triggering with Interpolated Samples
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Solution Overview
Problem
Digital oscilloscopes face issues with phase errors and jitter due to temporal discretization and stochastic phase noise, as well as different transit times in measurement channels, leading to inaccurate signal representation and potential failure in triggering.
Innovation Solution
A digital trigger system that uses interpolated sample values to determine the exact trigger time by comparing digitized measurement signal sample values with a threshold, minimizing trigger offset through polyphase filters and iterative halving of time intervals, and compensating for transit time differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If analog trigger system is used with temporal discretization, then the oscilloscope can operate with finite sampling rate, but phase errors and jitter occur in the signal representation
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing additional sample values at predetermined positions between the original sample points. These pre-computed intermediate samples enable the system to determine trigger points with higher precision without increasing the actual sampling rate, thereby resolving the contradiction between operational productivity and measurement precision.
Solution Approach 2:
The patent introduces an additional temporal dimension by inserting extra sample points between the original discrete samples. This dimensional expansion allows the system to achieve finer time resolution and more accurate phase measurement while maintaining the same base sampling rate, effectively decoupling precision from the fundamental sampling frequency.
2Reliability
If trigger offset occurs between samples, then the trigger point can be identified, but phase shift and jitter are introduced in the displayed signal
Solution Approach 1:
The patent uses additional sample values as intermediary elements between the original samples. These intermediate samples serve as mediators that enable precise trigger point identification without causing phase shift or jitter. The intermediaries fill the temporal gaps between samples, allowing accurate triggering while maintaining signal integrity in the display.
3Adaptability or versatility
If different propagation times exist in measurement channels, then multiple signals can be processed, but unwanted jitter and triggering failures occur
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing additional sample values at predetermined positions for each measurement channel. This advance preparation enables the system to compensate for different propagation times in multi-channel configurations, ensuring accurate triggering and eliminating unwanted jitter while maintaining the versatility of processing multiple signals simultaneously.
4Measurement precision
If phase errors are compensated through calibration, then some accuracy can be restored, but calibration is often impossible in extreme cases
Solution Approach 1:
The patent implements self-service by having the system automatically generate and utilize additional sample values through a built-in calculation mechanism. This self-contained approach eliminates the need for external calibration procedures, as the system inherently compensates for phase errors using its own pre-computed samples, thereby achieving high measurement precision without complex calibration operations.
Data Source
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AI summary
The invention relates to a digital oscilloscope in which a level comparison is performed between two consecutive samples (Si,j, Si,j-1) of a reference signal (Si) and a threshold value (SWi) to determine a trigger time. At least one additional sample (Si,j', (Si,j'') of the reference signal (Si) is determined by interpolation between two consecutive samples (Si,j, Si,ji) of the reference signal (Si).