Adjustable Symbol Clock Cable Tester for Long-Range Impedance Detection
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Solution Overview
Problem
Conventional cable testers struggle to accurately determine cable length and characterize transmission lines beyond 400 meters, especially when impedance mismatches are small and reflections are masked by noise or interference.
Innovation Solution
A cable tester with an adjustable symbol clock rate that uses digital signal processing (DSP) methods to inject a training signal into the cable, sample and adaptively filter the reflected signal, and determine cable characteristics such as impedance discontinuities and length, even with small reflections, by adjusting the symbol clock rate to increase the characterization length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the TDR method is used to determine cable length, then the measurement can be performed up to about 400 meters with large impedance mismatches, but small reflections from mis-matched terminations are missed when masked by noise
Solution Approach 1:
The patent applies dynamics by making the symbol clock rate adjustable rather than fixed. The cable tester dynamically adapts the symbol clock rate to match the cable length being tested, using lower symbol rates for longer cables to maintain signal integrity and detection accuracy throughout the extended range beyond 400 meters.
Solution Approach 2:
The patent changes the parameter of symbol clock rate to resolve the contradiction. By adjusting the symbol clock rate based on cable length, the system maintains reliable detection of small reflections from mis-matched terminations even at distances exceeding 400 meters, where fixed-rate systems would fail due to noise masking.
2Length of stationary object
If a fixed data symbol clock rate is used in the cable tester, then the device structure is simple, but the cable characterization distance is limited to about 400 meters
Solution Approach 1:
The cable tester incorporates a variable symbol clock rate mechanism that dynamically adjusts the clock rate based on the cable length being tested. This dynamic adjustment capability extends the characterization distance beyond 400 meters while managing the increased device complexity through adaptive control.
Solution Approach 2:
The system changes the operational parameter of symbol clock rate to extend cable characterization distance. By implementing adjustable symbol rates, the patent achieves extended measurement range while the complexity is managed through parameter adaptation rather than structural over-engineering.
3Productivity
If the symbol clock rate is increased to improve measurement speed, then the productivity is improved, but the cable length measurement accuracy decreases for long cables
Solution Approach 1:
The patent implements dynamic symbol clock rate adjustment where the clock rate is adapted to the cable length being measured. For longer cables, lower symbol rates are used to maintain signal integrity and measurement accuracy, while shorter cables can utilize higher symbol rates for faster measurement, thus resolving the trade-off between speed and accuracy.
Solution Approach 2:
The system changes the symbol clock rate parameter based on cable length to optimize both measurement speed and accuracy. By adjusting this parameter dynamically, the patent achieves accurate measurements for long cables without permanently sacrificing measurement speed, as higher rates can be used when appropriate.
Data Source
AI summary
Aspects of the present disclosure provide for a cable tester that tests a cable to determine the cable length. The cable tester can include a clock generator that generates a clock that has clock period that is a multiple of the data symbol period and a signal generator that injects the training signal, which can be synchronous with the clock, into the cable. The cable tester can also include a receiver that samples the returned signal from the cable and adaptively filters the returned signal based on the training signal and a controller that determines the cable length from the adaptive filter tap coefficients.