Differential Comparator Timing Compensation for Line Skew
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Solution Overview
Problem
Existing differential signal testing systems face challenges in accurately evaluating signals due to imbalances in differential line lengths, leading to erroneous transition time determinations and difficulties in evaluating true waveforms, especially when using variable-length coaxial cables or twisted pair lines.
Innovation Solution
A differential comparator with adjustable sampling timings for its sample hold circuits and latch circuit, allowing for independent timing control to cancel line length errors, ensuring proper evaluation of pure differential signals from devices under test.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable-length coaxial cables or twisted pair lines are used to connect the device under test and the differential comparator, then adaptability to different line length configurations is improved, but measurement precision of transition time deteriorates due to line length imbalances
Solution Approach 1:
The patent changes the timing parameter of signal sampling to compensate for line length imbalances. By adjusting the sampling timing of each differential signal independently, the system compensates for different propagation delays caused by varying line lengths, thereby maintaining measurement precision while preserving adaptability to different cable configurations
Solution Approach 2:
The patent performs preliminary timing adjustment of the sampling clocks before actual measurement. The sampling timing is pre-adjusted based on expected line length differences, so that when signals with different propagation delays arrive at the comparator, they are sampled at appropriately staggered times to compensate for the imbalance, thus eliminating the need for mechanical cable length adjustment
2Device complexity
If traditional differential comparator with fixed sampling timing is used, then device complexity is reduced, but measurement precision deteriorates when differential line lengths are unequal
Solution Approach 1:
The patent introduces dynamic timing adjustment capability to the differential comparator. Instead of fixed sampling timing, the system uses adjustable sampling clocks that can be dynamically configured to match the specific line length conditions, achieving high measurement precision while maintaining relatively simple circuit implementation through straightforward timing control mechanisms
3Measurement precision
If mechanical adjustment of cable length is performed to balance differential lines, then measurement precision is improved, but productivity and ease of operation deteriorate due to time-consuming adjustment process
Solution Approach 1:
The patent replaces the mechanical cable length adjustment system with an electrical timing adjustment system. Instead of physically changing cable lengths to achieve balance, the system uses electronically adjustable sampling timings to compensate for line length differences, thereby achieving differential line balance instantly without any mechanical intervention, significantly improving test setup speed and productivity
Data Source
AI summary
One of differential signals is inputted to a first input terminal. The other of the differential signals is inputted to a second input terminal. A first sample hold circuit samples the signal inputted to the first input terminal and hold it thereafter. A second sample hold circuit samples the signal inputted to the second input terminal and holds it thereafter. A comparison unit compares a signal corresponding to a difference between respective output signals from the first and the second sample hold circuits, with a predetermined threshold value. A latch circuit latches an output from the comparison unit. Sample timings of the first and the second sample hold circuits and a latch timing of the latch circuit can be adjusted independently.