Electronic Distance Meter Pulse Time Detection Circuit
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Solution Overview
Problem
Current laser-based electronic distance meters (EDMs) face challenges in achieving submillimeter precision with nanosecond pulses due to time walk and cost constraints, as existing solutions either require expensive high-speed ADCs or are prone to uncertainty from brightness and noise variations.
Innovation Solution
The EDM employs a comparison circuit with an integrator and comparator, where the cross-point between the pulse signal and its integral is used for precise time position detection, minimizing sensitivity to signal level variations and noise, allowing for cost-effective and high-precision measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precise digital sampling with fast ADC is used, then measurement precision reaches millimeter level, but cost becomes extremely high
Solution Approach 1:
The patent replaces expensive high-speed ADCs with a much cheaper comparator circuit that performs pulse time detection through voltage threshold comparison. The comparator is a low-cost component that can operate at the required speeds without the complexity and cost of high-speed analog-to-digital converters, achieving millimeter-level precision at a fraction of the cost.
Solution Approach 2:
The patent substitutes the electronic sampling and digital processing system (ADC + FPGA) with a simpler voltage comparison mechanism. Instead of converting the pulse to digital values and processing it computationally, the system uses an analog voltage comparator to directly determine pulse timing through voltage threshold crossing, eliminating the need for expensive high-speed conversion and digital processing hardware.
2Ease of manufacture
If threshold comparison is used for pulse time detection, then device cost is reduced, but time walk uncertainty increases making millimeter precision unachievable
Solution Approach 1:
The patent implements a feedback mechanism where the detected pulse time information is used to dynamically adjust the voltage threshold level. By continuously monitoring the pulse characteristics and adapting the threshold accordingly, the system compensates for variations in pulse amplitude and timing, thereby eliminating time walk error and achieving stable millimeter-level precision despite using a low-cost comparator.
3Measurement precision
If gigahertz clocks are used for nanosecond pulse treatment, then measurement precision is improved, but digital processing becomes impractical and costly
Solution Approach 1:
The patent replaces the complex gigahertz digital processing system with a simpler analog voltage comparison approach. Instead of sampling the pulse at gigahertz rates and processing the digital data, the system uses a comparator to detect the voltage threshold crossing point, which naturally provides nanosecond timing resolution without requiring high-speed digital sampling and complex synchronization logic.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise, real-time, and cost-effective submillimeter resolution EDMs with nanosecond pulse handling, independent of walk time, while maintaining high speed and accuracy.
Implementation Method 1
a photodetector adapted for receiving a laser pulse reflected by the target and for outputting a corresponding return pulse signal
Implementation Method 2
a comparison circuit receiving said return pulse signal and comprising a comparator provided with a first input and a second input... and a second branch connected to said second input which receives a signal derived from said return pulse signal
Data Source
Figure 1~3
Figure 4
AI summary
An electronic distance meter comprises a laser (4) emitting a laser pulse toward a target (12), a photodetector (6) adapted for receiving a laser pulse reflected by the target (12) and for outputting a corresponding return pulse signal, and a comparison circuit (8) receiving said return pulse signal and comprising a comparator provided with a first input and a second input and arranged to output a first fixed value signal when the signal at the first input exceeds the signal at the second input and else to output a second fixed value signal, said comparison circuit being arranged for determining a return pulse time signal based on the output of said comparator, said electronic distance meter being arranged for determining a target distance based on said return pulse time signal. The comparison circuit (8) comprises a first branch connected to said first input and provided with an integrator which receives a signal derived from said return pulse signal and comprises an output connected to said first input, and a second branch connected to said second input which receives a signal derived from said return pulse signal.