VCSEL Laser Driver Using FET Capacitance for Multi-Channel Pulsing
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Solution Overview
Problem
Conventional laser drivers for VCSELs have complex structures and high costs due to the use of multiple capacitors per channel, leading to increased manufacturing complexity, physical constraints, and reduced accuracy in range detection and measurement.
Innovation Solution
A laser driver design that integrates a high-side and low-side switch with an internal capacitor, eliminating the need for separate capacitors, optimizing capacitance in the FETs, and utilizing the FET's capacitance for charging and discharging, thereby improving speed without additional costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If individual capacitors are used for each channel to inject current into the diode, then the laser driver can drive multiple channels, but the structure becomes complex and manufacturing cost increases
Solution Approach 1:
The patent merges the capacitor function into the FET switch by utilizing the FET's internal capacitance (Cds and Cgs) to perform charge and discharge operations. This eliminates the need for separate external capacitors for each channel, reducing structural complexity while maintaining multi-channel driving capability. The FET's internal capacitance serves dual purposes: switching function and current pulse generation for laser diode driving.
Solution Approach 2:
The FET switch is designed to perform multiple functions: it acts as both the switching element and the capacitor for current injection. The internal capacitance of the FET (particularly Cds between drain and source, and Cgs between gate and source) is utilized to store and release charge, enabling the FET to serve as a universal component that combines switching and energy storage functions, thereby simplifying the overall circuit structure.
2Ease of manufacture
If individual capacitors are used for each channel, then current can be injected into the diode, but manufacturing cost increases
Solution Approach 1:
The patent combines the capacitor function with the FET switch by utilizing the FET's internal capacitance. This merger eliminates the need for separate external capacitors, reducing the number of components that need to be manufactured and assembled, thereby lowering manufacturing costs while maintaining the current injection capability necessary for diode operation.
Solution Approach 2:
The FET's internal capacitance serves the dual purpose of switching and energy storage without requiring external components. The internal capacitance (Cds and Cgs) of the FET itself provides the necessary charge storage and release functionality, making the system self-sufficient and eliminating the need for additional capacitors, thus reducing manufacturing complexity and cost.
3Productivity
If capacitors are configured for respective channels, then charge/discharge rate can be improved with inductors, but the control of LC time constant becomes more complicated
Solution Approach 1:
The patent extracts the capacitor function from external components and integrates it into the FET's internal structure. By removing the need for external capacitors and inductors, the system eliminates the complex LC time constant control requirements while maintaining fast charge/discharge rates through the FET's inherent switching capabilities and internal capacitance.
Solution Approach 2:
The patent changes the fundamental parameters of the system by transitioning from external LC circuits to utilizing the FET's internal capacitance. This parameter change eliminates the need for inductor-capacitor time constant control, simplifying the system while maintaining or improving charge/discharge rates through optimized FET switching parameters and internal capacitance characteristics.
4Ease of manufacture
If separate capacitors are used per channel, then current pulse can be generated, but the number of devices increases causing physical constraints
Solution Approach 1:
The patent merges the capacitor and switch functions into a single FET component by utilizing its internal capacitance. This consolidation reduces the number of discrete devices from multiple capacitors plus switches to just the FET switches themselves, eliminating physical constraints associated with housing multiple components while maintaining current pulse generation capability through the FET's internal charge storage and release mechanisms.
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
The new design enhances laser output and waveform quality, increasing detection range and accuracy in LiDAR systems by minimizing signal line resistance and optimizing capacitance.
Implementation Method 1
a high-side switch (High-side Field Effect Transistor (H.FET)) having an internal capacitor for charging with a drain terminal thereof connected to a high-voltage terminal
Implementation Method 2
when the high-side switch is open and the low-side switch is closed, the internal capacitor may be charged by the voltage applied from the high-voltage terminal. when the high-side switch is closed and the low-side switch is open, the charge in the internal capacitor may be discharged through transfer toward the VCSEL diode
Implementation Method 3
a VCSEL diode having an anode terminal connected to the high-side switch
Data Source
AI summary
A laser driver for driving a Vertical Cavity Surface Emitting Laser (VCSEL) includes a high-side switch (High-side Field Effect Transistor) having an internal capacitor for charging with a drain terminal thereof connected to a high-voltage terminal, a low-side switch (Low-side Field Effect Transistor) in which a drain terminal thereof is connected to a source terminal of the high-side switch and a source terminal thereof is connected to a ground terminal, and a VCSEL diode having an anode terminal connected to the high-side switch.