Laser Driver Clamping Circuit for Short Pulses Without Ringing
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Solution Overview
Problem
Existing laser driver circuits fail to produce laser pulses with sufficiently short pulse widths, high peak currents, and rapid repetition rates necessary for accurate time-of-flight ranging applications, while also preventing unwanted oscillations and maintaining efficient energy use.
Innovation Solution
A laser driver circuit incorporating a clamping circuit with a current source and clamping transistors to control the voltage at the output node, allowing for underdamped operation and rapid switching to minimize pulse width and increase repetition rate, while using clamping circuits to dampen oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the drive pulse fall is made sharp to reduce pulse width, then the pulse width and ranging accuracy are improved, but oscillations (ringing) occur in the drive current causing unwanted laser pulses
Solution Approach 1:
A clamping circuit is introduced as an intermediary component between the laser diode and the drive circuit. This clamping circuit includes a clamping transistor and associated components that actively clamp the drive current waveform during the fall edge, preventing oscillations without compromising the sharpness of the pulse fall. The clamping circuit mediates between the conflicting requirements of sharp pulse termination and oscillation suppression.
Solution Approach 2:
The invention dynamically changes the electrical parameters (voltage and current) at the laser diode during operation. The clamping circuit modifies the drive current waveform parameters by clamping it to a predetermined level during the fall edge, thereby controlling the oscillation amplitude and frequency while maintaining the desired pulse width characteristics.
2Productivity
If the drive pulse width is reduced to increase repetition rate, then the ranging accuracy and frame rate are improved, but the laser diode turn-on time becomes a limiting factor
Solution Approach 1:
The clamping circuit is activated in advance during the drive pulse fall edge, before the laser diode fully turns off. This preliminary action of clamping the current waveform helps to quickly reduce the current below the lasing threshold, effectively reducing the turn-off time and enabling higher repetition rates.
3Object-generated harmful factors
If the drive pulse fall is made slow to prevent oscillations, then oscillation suppression is improved, but energy efficiency deteriorates due to extended current flow duration
Solution Approach 1:
The clamping circuit serves as an intermediary that enables a sharp pulse fall while preventing oscillations. By actively clamping the current waveform, it achieves both objectives simultaneously: maintaining energy efficiency through sharp termination and suppressing oscillations through controlled current limiting.
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 proposed solution enables the generation of laser pulses with reduced pulse widths, higher peak currents, and faster repetition rates, enhancing the accuracy and efficiency of time-of-flight ranging systems by minimizing oscillations and reducing turn-on times.
Implementation Method 1
The at least one clamping circuit is configured to clamp voltage at the output node occurring in response to switching of the current source from turned on to turned off
Implementation Method 2
a laser diode (typically infrared) that is driven with a pulsed drive current to cause it to emit a short laser pulse
Data Source
AI summary
An input is coupled to a cathode of a laser diode having its anode coupled to a high-voltage-supply, with a cascoded current mirror having an input and output branches. The input branch is coupled between the high-voltage-supply and a sense resistor coupled to the input. The output branch is coupled between the high-voltage-supply and an output. A sense resistance is coupled between the output and ground, and includes a diode-coupled transistor coupled to the output and a resistor coupled between the diode-coupled transistor and ground. The input branch generates a current proportional to a voltage across the laser diode, and the output branch generates a mirrored current proportional to the current proportional to the voltage across the laser diode. A voltage proportional to the voltage across the laser diode is generated by the mirrored current flowing through the sense resistance. A comparison circuit compares this voltage to a threshold.