Voltage Mode Laser Diode Driver Circuit for Depth Cameras
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Solution Overview
Problem
Current laser diode drivers for depth cameras face issues with power efficiency, inductive kickback, and latency variations, leading to measurement errors and hardware damage, especially at high frequencies and powers.
Innovation Solution
A voltage mode laser diode driver with an active swing controller that selectively turns the laser diode on and off, preventing inductive kickback and optimizing power efficiency by adjusting the voltage level to match impedance and control current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If current mode laser diode drivers are used to control laser diode power, then laser diode power can be easily controlled by adjusting current source, but power efficiency is poor because only a small part of the power supply voltage drop is across the laser diode
Solution Approach 1:
The patent replaces the current mode control mechanism with a voltage mode control mechanism. Instead of controlling laser diode power through current source adjustment, the invention uses voltage modulation signals to control switching transistors that directly switch voltage to the laser diode, thereby improving power efficiency by ensuring the majority of the voltage drop occurs across the laser diode rather than in the control circuitry
Solution Approach 2:
The patent changes the control parameter from current to voltage. The modulation signal controls the switching transistor gate voltage, which in turn controls the current flow to the laser diode. This parameter change allows the system to achieve better power efficiency while maintaining ease of control through voltage-based modulation
2Measurement precision
If switching frequency is increased to improve depth measurement precision, then modulation frequency increases, but inductive kickback becomes more severe and can damage circuitry
Solution Approach 1:
The patent applies preliminary anti-action by incorporating a clamping diode connected to the laser diode cathode that is pre-configured to conduct when the cathode voltage exceeds a safe threshold. This diode actively prevents inductive kickback voltage spikes from damaging the circuitry, allowing the system to operate at high switching frequencies needed for precise depth measurement without suffering from voltage damage
Solution Approach 2:
The clamping diode serves as an intermediary protective element between the inductive kickback voltage spikes and the vulnerable circuitry. When high-frequency switching causes voltage overshoot, the diode intercepts and shunts the excess voltage, protecting the switching transistors and other components from damage while allowing high-frequency operation to continue
3Power
If voltage is increased to improve light power output, then laser power increases, but power efficiency decreases due to voltage drop across switching transistors
Solution Approach 1:
The patent replaces resistive voltage control with switching-based voltage control. Instead of using linear regulators or variable resistance to control voltage, the system uses fast switching transistors that operate in saturation/cutoff modes, minimizing the voltage drop across the control elements and maximizing the voltage available to the laser diode, thereby improving overall power efficiency
Solution Approach 2:
The patent employs periodic switching action at high frequencies to control the average power delivered to the laser diode. By rapidly switching the voltage on and off according to a modulation signal, the system achieves precise power control while maintaining high efficiency, as the switching elements spend minimal time in their linear (power-dissipating) region
Data Source
AI summary
A voltage mode laser diode driver selectively turns on and off a laser diode. An output stage has an output node configured to be connected to one of the terminals of the laser diode. Depending upon implementation, an active swing controller drives the output stage in a manner that substantially prevents inductive kickback from causing the output node voltage to swinging above the voltage level at the voltage output of the power supply, or swing below ground. The output stage provides a discharge path around the laser diode to shunt current associated with the inductive kickback, and substantially eliminates ringing on the output node of the output stage while the laser diode is off. A power supply controller adjusts the voltage level of the voltage output of the power supply so that current through the laser diode when on and emitting light is substantially equal to a predetermined desired current.