VCSEL Driving Circuit Residual Charge Discharge
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Solution Overview
Problem
Existing driving schemes for VCSELs in portable devices result in residual charge leading to prolonged optical pulse tails, degrading depth mapping performance in time-of-flight measurements due to high power consumption and thermal dissipation issues.
Innovation Solution
A low-power, unidirectional driving architecture utilizing a discharge switch connected in parallel with the VCSEL, triggered by current pulses to rapidly discharge residual charge, ensuring sharp optical pulse termination with a high-speed discharge switch and control circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional driving scheme is used for VCSELs, then the device can operate, but residual charge accumulates causing prolonged optical pulse tails that degrade depth mapping performance
Solution Approach 1:
The patent extracts and removes the residual charge from the VCSEL structure by introducing a discharge path through a discharge switch connected between the cathode and anode. This extraction mechanism actively removes the harmful residual charge that would otherwise cause prolonged optical pulse tails, thereby sharpening the pulse termination and improving depth mapping resolution.
Solution Approach 2:
The discharge switch is activated in advance to counteract the residual charge accumulation before it can significantly degrade the optical pulse shape. By applying a reverse bias voltage through the discharge switch immediately after the drive pulse ends, the system preemptively neutralizes the residual charge, preventing the formation of long pulse tails and maintaining sharp pulse edges for accurate depth mapping.
2Duration of action of moving object
If high power is used to drive VCSELs for short pulses, then pulse duration is reduced, but power consumption and thermal dissipation increase
Solution Approach 1:
The patent employs periodic pulsed operation where the VCSEL is driven in short bursts followed by discharge intervals. The drive switch activates the VCSEL for brief periods to generate optical pulses, then the discharge switch activates to remove residual charge during off-periods. This periodic on-off-discharge cycle allows the system to maintain short pulse durations without continuous high power consumption, as the discharge phase consumes minimal power compared to continuous high-power driving.
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 effectively terminates optical pulses with a sharp falling edge, improving depth mapping resolution and reducing power consumption and thermal dissipation in portable devices.
Implementation Method 1
A discharge switch has a first switch terminal connected to the cathode terminal and a second switch terminal connected to a discharge voltage... configured, when closed, to raise the cathode terminal to the discharge voltage
Data Source
AI summary
An optoelectronic device includes a laser diode having a cathode terminal and an anode terminal, which is connected to a driving voltage. A driver is coupled to drive current pulses through the laser diode from the anode terminal to the cathode terminal. A discharge switch has a first switch terminal connected to the cathode terminal and a second switch terminal connected to a discharge voltage, which is equal to or greater than the driving voltage, and is configured, when closed, to raise the cathode terminal to the discharge voltage. A switch control circuit has an input connected to the cathode terminal and an output connected to close the discharge switch in response to the current pulses occurring at the input.