Capacitive Unit for ToF Light-Emitting Apparatus Drive Speed
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Solution Overview
Problem
In Time of Flight (ToF) sensors, particularly in mobile devices, there is a challenge in achieving high spatial resolution and power saving while simultaneously switching multiple light-emitting elements in parallel with a drive current of a few A and high-speed pulses, as the time taken for the current to reach a predetermined power level is prolonged due to parasitic inductance in the drive current route.
Innovation Solution
A light-emitting apparatus is designed with a capacitive unit provided in parallel with the drive current route between the anode and cathode electrodes of the light-emitting element, which reduces the time for current to reach a predetermined power level by accumulating and releasing electric charge efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple light-emitting elements are simultaneously switched in parallel with high-speed pulses to achieve high spatial resolution and power saving, then the drive speed and power efficiency are improved, but the time taken for current to reach a predetermined power level is prolonged due to parasitic inductance
Solution Approach 1:
The capacitive element stores electric charge in advance during a charging period. When the light-emitting element needs to be driven, the stored charge is immediately discharged to provide the required drive current, eliminating the delay caused by parasitic inductance. This preliminary charging action enables high-speed switching while maintaining sufficient current magnitude.
Solution Approach 2:
The capacitive element acts as an intermediary between the power supply and the light-emitting element. It mediates the current delivery by storing and releasing charge as needed, effectively decoupling the drive circuit from the limitations of parasitic inductance in the wiring. This intermediary component enables fast current delivery without being constrained by the inductance of the drive current route.
2Speed
If a capacitive element is provided on the substrate to supply drive current, then the inductance of the drive circuit is reduced, but the device complexity and area are increased
Solution Approach 1:
The capacitive element is integrated with the drive circuit wiring structure. The capacitance is formed by utilizing the wiring layers and insulating films already present in the semiconductor device structure, merging the capacitive function with the existing drive circuit rather than adding completely separate components. This reduces device complexity while maintaining the speed benefits.
Solution Approach 2:
The wiring structure serves multiple functions: it acts as both the drive current pathway and as one of the electrodes forming the capacitive element. The insulating films and wiring layers perform both their original electrical connection function and serve as components of the capacitive storage element. This multi-functionality reduces the need for additional dedicated components.
3Reliability
If the cathode side is connected to an element with realistic configuration, then the drain voltage drops due to parasitic inductance of the drive current route, but the time from when current is first consumed by light emission until a predetermined power is reached is prolonged
Solution Approach 1:
The capacitive element pre-stores the charge needed for the drive current. When switching occurs, this pre-stored charge is immediately released to the light-emitting element, providing the necessary current magnitude without being limited by the parasitic inductance of the cathode connection route. This preliminary charge storage enables both reliable constant current operation and fast response time.
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 significantly reduces the time from when current is first consumed by light emission until a predetermined power is reached, enhancing the drive speed and efficiency of light-emitting elements in ToF sensors.
Implementation Method 1
a capacitive unit provided in parallel with a route of current that causes light emission, between an anode electrode provided on an anode side of the light-emitting element and the cathode electrode
Data Source
AI summary
A light-emitting apparatus includes: a light-emitting unit including a light-emitting element; a drive unit including a first element connected to a cathode electrode provided on a cathode side of the light-emitting element, the drive unit being configured to drive the light-emitting element by supplying current that causes light emission; and a capacitive unit provided in parallel with a route of current that causes light emission, between an anode electrode provided on an anode side of the light-emitting element and the cathode electrode.