Laser Driver Layout With Integrated Capacitor for Fast ToF Pulsing
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Solution Overview
Problem
Measurement devices using the Time of Flight (ToF) method for three-dimensional shape measurement require reduced inductance of the driving circuit and efficient heat release from the laser unit to achieve shorter rise time and higher accuracy, which is challenging with conventional configurations where capacitive elements are external to the substrate.
Innovation Solution
A light-emitting device with a capacitive element integrated on a first base member, a laser unit, and a wiring board with lower thermal conductivity, where the driving unit and capacitors are mounted on the wiring board to shorten the driving circuit and enhance heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the capacitive element is provided outside the first substrate, then the device complexity is reduced, but the inductance of the driving circuit increases and heat release from the laser unit becomes inefficient
Solution Approach 1:
The patent merges the capacitive element with the first substrate by forming it as an integrated structure within the substrate. This integration reduces the distance between the capacitor and the laser unit, thereby reducing circuit inductance and improving heat release efficiency, while maintaining device complexity at an acceptable level through the integrated design approach.
Solution Approach 2:
The patent utilizes the vertical dimension by forming the capacitive element as a three-dimensional structure (such as a capacitor with upper and lower electrodes extending in the thickness direction) within the substrate. This dimensional approach allows the capacitor to be embedded in the substrate without increasing planar area, reducing inductance through shorter current paths while managing heat dissipation in the vertical direction.
2Reliability
If the capacitive element is integrated on the first base member, then the inductance is reduced and heat release is improved, but the device complexity increases
Solution Approach 1:
The capacitive element is merged with the first substrate as an integrated structure, where the capacitor is formed using the substrate material itself or layers within the substrate. This integration reduces inductance by minimizing the current path length while the substrate serves dual functions as both structural support and capacitive element housing, thereby managing device complexity.
Solution Approach 2:
The first substrate serves multiple functions: it provides mechanical support, acts as a mounting platform for the laser unit, and contains the capacitive element. This multi-functionality reduces the need for separate components, thereby managing device complexity while achieving low inductance and improved heat release through the integrated design.
3Temperature
If the wiring board has higher thermal conductivity, then heat release is improved, but the measurement precision of the ToF method deteriorates due to thermal interference
Solution Approach 1:
The patent applies local quality by providing high thermal conductivity specifically at the laser unit mounting area (first substrate) for efficient heat release, while the wiring board has lower thermal conductivity to minimize thermal interference with the ToF measurement. This spatial differentiation of thermal properties allows simultaneous optimization of heat release and measurement precision.
Solution Approach 2:
The patent segments the thermal management function by separating the heat release path (through the first substrate with high thermal conductivity) from the measurement path (wiring board with lower thermal conductivity). This segmentation allows the laser unit to be thermally managed independently from the measurement system, preventing thermal interference while maintaining efficient heat dissipation.
4Loss of time
If the driving circuit is shortened, then the rise time is reduced, but the device complexity increases due to integrated mounting
Solution Approach 1:
The driving unit and capacitive element are merged with the first substrate through integrated mounting, where these components are positioned in close proximity or directly mounted on the substrate. This spatial merging shortens the driving circuit length, reducing inductance and rise time, while the integrated mounting approach manages device complexity through unified structural design.
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 configuration reduces circuit inductance, shortens the rise time of light emission, and efficiently releases heat, improving the accuracy and reliability of three-dimensional shape measurement in devices like face authentication and augmented reality applications.
Implementation Method 1
a capacitive element that is provided on the first base member and supplies a driving electric current to the laser unit
Implementation Method 2
a wiring board that is constituted by a second base member having lower thermal conductivity than the first base member and on which the first base member is mounted
Data Source
AI summary
A light-emitting device includes a first base member; a laser unit provided on the first base member; a capacitive element that is provided on the first base member and supplies a driving electric current to the laser unit; a wiring board that is constituted by a second base member having lower thermal conductivity than the first base member and on which the first base member is mounted; and a driving unit that is mounted on the wiring board and drives the laser unit.