Resonant Laser Driver Circuit for ToF Depth Calibration
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Solution Overview
Problem
Time-of-flight (ToF) 3D imaging using continuous-wave (CW) approaches with square waves is inefficient and suffers from harmonic content issues, making depth calibration difficult, while generating sinusoidal waves poses challenges in driver design.
Innovation Solution
A resonant laser diode driver circuit that utilizes parasitic inductance and capacitance to filter square wave signals into sinusoidal waves, with a bias circuit and tunable amplitude to minimize harmonic distortion and optimize driver performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a square wave is used to drive the laser diode in ToF imaging, then the driver circuit is easily realizable using digital circuits, but the efficiency is reduced and harmonic contents cause difficulty in depth calibration
Solution Approach 1:
The patent introduces an LC resonant circuit as an intermediary component between the digital square wave generator and the laser diode. This resonant circuit acts as a mediator that transforms the square wave signal into a sinusoidal waveform, thereby eliminating harmonic distortion while maintaining compatibility with digital circuit implementation. The LC tank circuit naturally filters out higher frequency harmonics and produces a clean sinusoidal output that is ideal for ToF depth calibration.
Solution Approach 2:
The patent changes the signal waveform parameter from square wave to sinusoidal wave by utilizing the resonant properties of the LC circuit. By adjusting the resonant frequency of the LC tank to match the drive frequency, the system transforms the signal characteristics to achieve low harmonic distortion while maintaining ease of digital implementation through frequency-domain transformation rather than time-domain waveform generation.
2Measurement precision
If a sinusoidal wave is used to drive the laser diode, then the depth performance is improved with better linearity and no harmonic distortion, but the driver design becomes more challenging
Solution Approach 1:
The LC resonant circuit serves as a passive intermediary that automatically generates the sinusoidal waveform without requiring complex active circuitry. The resonant tank naturally oscillates at its resonant frequency when excited by a square wave, providing a clean sinusoidal output that drives the laser diode with minimal harmonic distortion, thus achieving high measurement precision without increasing driver complexity.
Solution Approach 2:
The LC resonant circuit is self-regulating and automatically produces the sinusoidal waveform through its inherent resonant properties. Once excited by the square wave input, the tank circuit self-oscillates at its natural resonant frequency, eliminating the need for additional control circuits or complex feedback mechanisms to generate the sinusoidal signal, thereby keeping the driver design simple.
3Measurement precision
If a resonant circuit is used to generate sinusoidal waves, then the total harmonic distortion is reduced, but additional circuit components are required
Solution Approach 1:
The LC resonant circuit is introduced as a minimal intermediary component that provides significant signal purification. The simple series LC tank circuit, consisting of only one inductor and one capacitor, effectively filters out harmonic frequencies and produces a clean sinusoidal waveform, achieving low total harmonic distortion with minimal additional components.
Solution Approach 2:
The patent uses passive LC components that are inexpensive and can be easily integrated into the driver circuit. The resonant circuit components are simple, low-cost passive elements that provide high signal purity without requiring expensive active components or complex circuit topologies, making the solution economically viable and easy to manufacture.
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 provides a highly integrated, low-cost driver circuit with low total harmonic distortion (THD) for sinusoidal signals, enabling efficient and accurate depth measurement in ToF sensors.
Implementation Method 1
a resonant circuit (310) arranged to filter the drive signal to provide the continuous wave sinusoidal signal to the laser diode
Implementation Method 2
laser diode (202) arranged to be driven by the continuous wave sinusoidal signal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A laser emitter circuit comprises a laser diode; a driver circuit configured to generate a drive signal; and a resonant circuit coupled to the driver circuit and the laser diode, wherein the resonant circuit is configured to use the drive signal of the driver circuit to generate a continuous wave sinusoidal drive signal to drive the laser diode.