Fractional Delay Measurement Using Time Vernier Effect
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Solution Overview
Problem
Conventional methods for measuring transmission medium delay have limited resolution, requiring more precise and costly equipment to achieve higher accuracy, which is not feasible with standard clocks.
Innovation Solution
The implementation of a time Vernier effect using a first clock for signal injection and a second clock for sampling, with a phase lock loop (PLL) and linear feedback shift registers (LFSRs) to generate pseudo-random sequences, allowing for fractional delay measurement with a 1 kHz clock, equivalent to resolutions of 1/10,000 seconds or even nanoseconds with GHz clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional delay measurement techniques are used with standard clocks, then the measurement process is simple and equipment is affordable, but the measurement resolution is limited to one integer clock cycle
Solution Approach 1:
The patent divides the delay measurement into two independent components: integer delay measurement (using standard clock cycles) and fractional delay measurement (using correlation techniques with pseudo-random sequences). This segmentation allows each component to be measured with appropriate precision without requiring an overly precise clock, thereby resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent introduces a pseudo-random sequence as an intermediary signal between the input and output of the transmission medium. By correlating the output sequence with a delayed version of the input sequence, the system can precisely determine fractional delays without requiring high-precision timing equipment, thus achieving high measurement precision without proportionally increasing device complexity
2Measurement precision
If more precise equipment is used to increase measurement resolution, then the delay measurement accuracy improves, but the cost becomes prohibitive
Solution Approach 1:
The patent uses inexpensive pseudo-random sequences generated by linear feedback shift registers (LFSRs) as the measurement probe instead of expensive high-precision timing equipment. These sequences are computationally generated and discarded after use, providing a cost-effective alternative to expensive hardware while achieving the same measurement accuracy
Solution Approach 2:
The patent replaces the mechanical/timing-based measurement approach (requiring precise clocks and timing circuits) with a signal-processing approach using correlation of pseudo-random sequences. This substitution eliminates the need for expensive high-precision timing equipment while maintaining or improving measurement accuracy
Data Source
AI summary
A measurement system may measure a fractional time delay of transmission of a signal across a medium, such as a cable. The system may use a first clock to assist in creating and injecting an injected sequence (signal) into the medium. A second, slower clock may be used for sampling the sequence after transmission of the sequence through the medium. This causes a time Vernier scale effect that results in a sampled sequence that has a one-step skip for each instances of the sequence, where the sequence has N elements in the sequence. The location of the skip within the sequence will depend on the magnitude of the delay measured as a fraction of a clock period with a resolution of N. To measure this delay, a modified version of a pseudo-random sequence generator, capable of skipping one step, is used to determine the output.