ISI Equalizer With Windowed Pulses for Jitter Measurement
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Solution Overview
Problem
Test and measurement systems struggle to accurately separate and measure uncorrelated jitter from intersymbol interference (ISI) in high-speed signals, particularly in pulse amplitude modulation formats like PAM4, due to the interaction of ISI and jitter, which complicates accurate waveform analysis.
Innovation Solution
Employing an ISI equalizer that uses a window function to extract a target pulse, followed by a linear equalizer generated via Least Mean Square (LMS) algorithm to mitigate ISI, allowing for precise uncorrelated jitter measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used to analyze high-speed signals, then the measurement system can capture the signal, but it cannot accurately separate uncorrelated jitter from intersymbol interference (ISI)
Solution Approach 1:
The patent segments the signal analysis process into distinct stages: first applying an ISI equalizer to remove intersymbol interference, then measuring uncorrelated jitter on the equalized signal. This segmentation allows the measurement system to isolate and measure jitter separately from ISI, achieving accurate jitter measurement without the complexity of trying to separate them simultaneously in the raw signal.
Solution Approach 2:
The patent introduces an ISI equalizer as an intermediary component between the signal source and the jitter measurement. This equalizer acts as a mediator that preprocesses the signal by removing ISI effects, thereby enabling the subsequent jitter measurement to be performed on a cleaned signal where uncorrelated jitter can be accurately extracted without contamination from ISI.
2Reliability
If the ISI equalizer processes the entire waveform, then ISI is reduced, but the processing time increases
Solution Approach 1:
The patent extracts only the necessary portion of the waveform for ISI equalization by identifying and processing individual pulses or pulse groups that contain the relevant ISI information. Instead of processing the entire continuous waveform, the system extracts discrete pulse segments, applies the equalizer to these extracted portions, and reconstructs the equalized signal, thereby reducing processing time while maintaining ISI reduction effectiveness.
Solution Approach 2:
The patent applies partial action by processing only the critical portions of the signal where ISI has the most significant impact. The equalizer is applied selectively to pulse transitions and critical timing regions rather than uniformly across the entire waveform, achieving sufficient ISI reduction for accurate jitter measurement while minimizing unnecessary processing overhead.
3Measurement precision
If a long bit sequence is used for jitter measurement, then measurement accuracy improves, but measurement duration increases
Solution Approach 1:
The patent performs preliminary action by applying the ISI equalizer to the signal before jitter measurement. This preprocessing step removes ISI effects that would otherwise contaminate the jitter measurement, allowing for accurate results to be obtained from shorter bit sequences. The equalized signal provides a cleaner basis for jitter analysis, reducing the need for extremely long measurement sequences.
Solution Approach 2:
The patent replaces the traditional mechanical approach of using long bit sequences to average out ISI effects with a signal processing approach. Instead of relying on statistical averaging over long sequences, the system uses the ISI equalizer to actively remove ISI effects from the signal, thereby achieving the same measurement accuracy with significantly shorter bit sequences and faster measurement times.
Data Source
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AI summary
Disclosed is a mechanism for limiting Intersymbol Interference (ISI) when measuring uncorrelated jitter in a test and measurement system. A waveform is obtained that describes a signal. Such waveform may be obtained from memory. A processor then extracts a signal pulse from the waveform. The processor selects a window function based on a shape of the signal pulse. Further, the processor applies the window function to the signal pulse to remove ISI outside a window of the window function while measuring waveform jitter. The window function may be applied by applying the window function to the signal pulse to obtain a target pulse. A linear equalizer is then generated that results in the target pulse when convolved with the signal pulse. The linear equalizer is then applied to the waveform to limit ISI for jitter measurement.