Optical Emitter Driver Circuit for Uniform TOF Pulse Control
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Solution Overview
Problem
Time-of-flight ranging devices face challenges in generating high-intensity, short-duration optical pulses due to parasitic inductances, capacitances, and resistances, leading to slow rise times and non-uniform pulse amplitudes, which can exceed laser safety limits and compromise depth uncertainty in distance measurements.
Innovation Solution
A driver circuit with an inductor, switches, and a current sensor is used to control the optical light emitter, employing pulse-width modulation and frequency control to regulate current and generate high-frequency, high-intensity optical pulses with uniform amplitude, while maintaining a low supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional current driving circuits are used to generate high-intensity optical pulses, then the optical pulse intensity increases, but the rise time becomes slow and pulse amplitudes become non-uniform due to parasitic inductances, capacitances, and resistances
Solution Approach 1:
The patent employs periodic switching of the optical light emitter at a frequency of at least 10 MHz to generate optical pulses. This periodic action allows precise control over pulse timing and duration, enabling high pulse repetition rates while maintaining uniform amplitude through regulated current delivery during each pulse cycle
Solution Approach 2:
The patent changes the operating parameters by implementing current regulation that maintains a lower supply voltage while delivering precise current pulses. This parameter change allows high optical pulse intensity to be achieved through optimized pulse width and frequency rather than continuously high voltage, thereby reducing parasitic effects and maintaining pulse uniformity
2Illumination intensity
If high current is driven through the optical light emitter to increase optical pulse intensity, then the optical output increases, but laser safety limits may be exceeded
Solution Approach 1:
By using periodic pulsed operation at high frequency (≥10 MHz) with controlled duty cycle, the system delivers high peak power optical pulses while maintaining lower average power. This temporal separation allows high instantaneous intensity for measurement accuracy while keeping overall energy exposure within safety limits through precise pulse width control
Solution Approach 2:
The patent implements parameter changes by regulating the current pulse width and frequency rather than using continuous high current. This allows the optical pulse intensity to be maximized during the pulse duration while the average current remains lower, ensuring compliance with laser safety standards through optimized temporal distribution of energy
3Illumination intensity
If high supply voltage is used to drive the optical light emitter, then optical pulse intensity increases, but the system complexity and safety requirements increase
Solution Approach 1:
The patent changes the approach by using regulated current pulses at lower supply voltage rather than unregulated high voltage. This parameter change simplifies the voltage regulation requirements while maintaining high optical pulse intensity through precise current control and optimized pulse timing, reducing both device complexity and safety requirements
4Use of energy by moving object
If pulse duration is extended to increase optical energy output, then the total energy increases, but the time resolution for depth measurement deteriorates
Solution Approach 1:
The system uses high-frequency periodic pulsing (≥10 MHz) with precise duty cycle control to deliver sufficient optical energy in each short pulse while maintaining brief pulse duration. This allows adequate photon return for detection while preserving sharp temporal resolution for accurate time-of-flight measurement and depth calculation
Solution Approach 2:
The patent optimizes the balance between energy and resolution by adjusting pulse width and repetition frequency as separate parameters. This allows the optical pulse energy to be sufficient for detection while keeping pulse duration short for high time resolution, achieving both goals through independent parameter optimization rather than relying on extended pulse duration
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 solution enables the generation of optical pulses with consistent and high power, improving depth uncertainty and ensuring compliance with laser safety limits by regulating current and maintaining a lower supply voltage.
Implementation Method 1
a current sensor configured to detect the current passing through the inductor and to provide a feedback signal to the current driver
Implementation Method 2
an optical light emitter, the above driver circuit causing the optical light emitter to generate optical light pulses
Implementation Method 3
Laser diodes, such as VCSELs, are light emitting devices capable of emitting light with an intensity that depends on a level of current driven through them
Data Source
AI summary
The present disclosure relates to a driver circuit for an optical light emitter of a ranging device, the driver circuit comprising: an inductor having a first of its nodes coupled to a current driver; a first branch comprising a first switch coupled between the second node of the inductor and a first supply voltage rail; a second branch for conducting a current through the optical light emitter, the second branch being coupled between the second node of the inductor and the first supply voltage rail; and a current sensor configured to detect the current passing through the inductor and to provide a feedback signal to the current driver.