Tapped Delay Line TDC for Multi-Threshold Pulse Timing
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Solution Overview
Problem
Conventional laser radar systems face challenges in achieving high time resolution for precise distance and pulse shape measurement, particularly due to the high cost and complexity associated with increasing clock speed, and the limitations of Time Over Threshold (TOT) methods in capturing detailed pulse information.
Innovation Solution
A Time-to-Digital Converter (TDC) using a tapped delay line and clock generator to measure time intervals, allowing for high-resolution timing measurements by subdividing the clock cycle and using multiple thresholds for pulse characterization, thereby reducing the need for high clock speeds and improving data accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If fast analog waveform sampling is used to gather comprehensive pulse data, then measurement information richness is improved, but computing power requirements and storage space increase considerably
Solution Approach 1:
The patent extracts only the essential measurement information (time of flight, pulse width, amplitude) using TOT measurements at specific thresholds rather than capturing the complete waveform. This extraction approach obtains sufficient measurement data while avoiding the computational burden of processing entire waveforms.
Solution Approach 2:
The patent uses a partial action approach by measuring only at specific threshold crossings (e.g., 10% and 90% amplitude points) rather than continuous sampling. This provides adequate measurement precision for laser radar applications without the excessive data collection and processing requirements of full waveform capture.
2Measurement precision
If fast analog waveform sampling is used to achieve sub-nanosecond timing resolution, then measurement precision is improved, but storage space requirements increase considerably
Solution Approach 1:
The patent extracts only the critical timing information (when pulse crosses specific thresholds) rather than storing complete waveform data. This provides sub-nanosecond timing resolution while minimizing storage requirements to just a few data points per pulse.
Solution Approach 2:
The patent uses partial sampling at strategically chosen thresholds to achieve high timing precision without excessive storage. By measuring only at key pulse characteristics (leading edge crossings at defined amplitude levels), it obtains sufficient precision for distance measurement without storing entire waveforms.
3Measurement precision
If clock speed is increased to achieve higher time resolution in TOT measurements, then measurement precision is improved, but system cost increases
Solution Approach 1:
The patent segments the time measurement function into multiple independent TOT channels, each measuring pulse width at a specific threshold level. This segmentation allows using slower, cheaper clocks for each channel while achieving high overall time resolution through the combination of multiple measurements and known pulse shape characteristics.
Solution Approach 2:
The patent changes the measurement parameter from direct time interval measurement with high-speed clocks to pulse width measurement at multiple amplitude thresholds. By utilizing the relationship between pulse width, amplitude, and shape, it achieves high time resolution using lower clock speeds, thereby reducing system cost.
4Device complexity
If conventional leading edge detection is used for time of flight measurement, then system simplicity is maintained, but distance measurement precision deteriorates due to pulse amplitude variations
Solution Approach 1:
The patent changes the detection parameter from fixed threshold leading edge detection to multiple threshold crossings at defined amplitude percentages (e.g., 10% and 90%). This accounts for pulse amplitude variations by measuring pulse width at standardized amplitude levels, improving distance precision while maintaining reasonable system complexity.
Solution Approach 2:
The patent performs preliminary measurement of pulse characteristics (amplitude, width at multiple thresholds) before calculating time of flight. This preliminary characterization of the pulse shape allows for more accurate distance determination by compensating for amplitude variations and pulse shape effects.
Data Source
AI summary
A method and apparatus for measuring the duration of a transient signal with high precision.