VCSEL Pulse Width Control Using Capacitor-Based Detection
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Solution Overview
Problem
The challenge in distance measurement using direct ToF methods is the need for high-precision clocks to achieve accurate pulse width detection, leading to increased circuit complexity and cost due to the small pulse widths of light-emitting elements.
Innovation Solution
A laser drive apparatus that adjusts pulse widths using a capacitor-based detection method, eliminating the need for high-speed clocks by measuring the capacitor's potential during charging, and utilizing a control unit to adjust pulse widths based on reference and actual measured potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-precision clock is used for pulse width detection in direct ToF method, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the traditional high-speed clock-based time measurement system with a capacitor charging-based measurement system. Instead of using a 100 GHz clock to measure the 1 ns pulse width directly, the system charges a capacitor during the pulse width period and measures the resulting voltage, substituting a mechanical/time-based measurement with an electrical/energy-based measurement that can be achieved with lower frequency clocks.
Solution Approach 2:
The patent transforms the measurement parameter from direct time measurement to voltage measurement. By charging a capacitor for a duration equal to the pulse width and then measuring the voltage across the capacitor, the system converts an extremely small time interval (1 ns) into a measurable voltage value that can be accurately detected using standard ADCs and lower frequency clocks.
2Measurement precision
If a high-precision clock is used for pulse width detection, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent replaces expensive high-speed clock circuits (100 GHz) with inexpensive capacitor charging circuits and standard ADCs. The capacitor charging circuit requires only basic electronic components that are inexpensive and widely available, eliminating the need for costly high-frequency clock generation and distribution infrastructure.
Solution Approach 2:
The patent uses a capacitor as a temporary, disposable energy storage element that is charged for the duration of the pulse width and then discharged for measurement. This approach uses inexpensive, readily available components rather than expensive, specialized high-speed timing circuits, significantly reducing the bill of materials cost.
3Measurement precision
If pulse width is made small for direct ToF method, then measurement precision is improved, but difficulty of detecting and measuring increases
Solution Approach 1:
The patent substitutes direct time measurement with voltage measurement. By charging a capacitor during the pulse width period, the extremely small time duration is converted into a voltage value that can be measured by standard ADCs operating at much lower frequencies, making the measurement process significantly easier and more practical.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the pulse width signal and the measurement system. The capacitor accumulates charge proportional to the pulse width duration and converts it into a voltage signal that can be easily measured and processed, serving as a bridge between the fast optical domain and the slower electronic measurement domain.
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 simplifies circuit configuration, reduces costs, and allows accurate pulse width adjustment without the need for high-precision clocks, while maintaining precision in distance measurement.
Implementation Method 1
a pulse width detection unit that detects the pulse width of the pulse signal on the basis of the potential of a capacitor when the capacitor is charged on the basis of the pulse signal
Data Source
AI summary
By eliminating the need to use a high-precision clock in pulse width detection for pulse width adjustment in a case where light-emitting elements as vertical-cavity surface-emitting lasers are pulse-driven, circuit configuration is simplified and cost is reduced. A laser drive apparatus according to the present technology includes a drive circuit unit that drives light-emitting elements as vertical-cavity surface-emitting lasers to emit light on the basis of a pulse signal, a pulse width detection unit that detects the pulse width of the pulse signal on the basis of the potential of a capacitor when the capacitor is charged on the basis of the pulse signal, and a control unit that performs control so that the pulse width is adjusted on the basis of a detection result of the pulse width.