Electro-Optical Phase Locked Loop for LIDAR Frequency Control
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Solution Overview
Problem
Conventional LIDAR systems face significant cost and complexity issues due to the need for high-power discrete circuit components to handle large currents for frequency modulation in coherent LIDAR techniques, which complicates the generation and control of optical beams for distance and speed measurement.
Innovation Solution
A simplified laser diode control circuit using an electro-optical phase locked loop (EOPLL) and operational amplifier (op-amp) to generate ramp signals, enabling a single-ended voltage-mode drive circuit that reduces the number of components and allows for integration into a smaller, more cost-effective integrated circuit, separating bias and modulation currents to minimize power consumption and component size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional frequency modulation using high current levels is used to excite the laser diode, then the laser diode can generate the required optical beam for distance and speed measurement, but the circuit components become larger and must be implemented as discrete elements, increasing system cost and complexity
Solution Approach 1:
The patent segments the current control into two independent parts: a bias current path and a modulation current path. The bias current (several hundred mA to 1 A) flows through the laser diode continuously, while the modulation current (small AC signal) is superimposed on it. This segmentation allows the high-power bias circuit to be separated from the low-power modulation circuit, enabling the modulation circuit to be integrated while the bias circuit remains discrete.
Solution Approach 2:
The patent introduces an intermediary approach by using a modulator that converts voltage signals to current signals. The modulator receives a voltage modulation signal and converts it to a modulation current that is added to the bias current. This intermediary device allows the use of low-power voltage circuitry (easy to integrate) to control the high-power laser diode current.
2Reliability
If high current levels are used to drive the laser diode for frequency modulation, then the optical beam can be generated effectively, but the circuitry requires higher-power discrete elements that increase system cost
Solution Approach 1:
The patent segments the current control into two independent parts: a bias current path and a modulation current path. The bias current (several hundred mA to 1 A) flows through the laser diode continuously, while the modulation current (small AC signal) is superimposed on it. This segmentation allows the high-power bias circuit to be separated from the low-power modulation circuit, enabling the modulation circuit to be integrated while the bias circuit remains discrete.
Solution Approach 2:
The patent changes the operational parameters by separating the DC bias current (high power) from the AC modulation current (low power). By controlling these as separate parameters with different power levels, the system can use integrated low-power circuitry for modulation while maintaining the necessary high-power bias current for reliable laser operation.
3Ease of operation
If conventional circuitry is used to handle large currents for frequency modulation, then the laser diode can be controlled effectively, but the number of higher-power components increases, reducing power efficiency
Solution Approach 1:
The patent segments the current control into two independent parts: a bias current path and a modulation current path. The bias current (several hundred mA to 1 A) flows through the laser diode continuously, while the modulation current (small AC signal) is superimposed on it. This segmentation allows the high-power bias circuit to be separated from the low-power modulation circuit, enabling the modulation circuit to be integrated while the bias circuit remains discrete.
Solution Approach 2:
The patent uses periodic modulation action by superimposing an AC modulation signal on the DC bias current. The modulation current varies periodically to create the frequency-modulated optical output. This periodic action allows the use of small-signal AC circuitry (low power) to control the high-power DC bias, improving overall power efficiency.
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 solution enables more compact, cost-effective, and power-efficient LIDAR systems capable of simultaneous distance and speed measurement, reducing the number of higher-power components and allowing for integration into smaller form factors while maintaining effective control over the laser diode.
Implementation Method 1
an electro-optical phase locked loop (EOPLL) configured to maintain the light at the target frequency
Implementation Method 2
an operational amplifier (op-amp) to generate ramp signals... a single-ended voltage-mode drive circuit that drives a current through the light source in response to a voltage signal from the op-amp
Implementation Method 3
The laser diode generates light at a wavelength that is proportional to the magnitude of the current through it
Implementation Method 4
Modulating the current in turn modulates the frequency of the light and generates the chirps
Data Source
AI summary
A frequency modulated continuous wave (FMCW) light detection and ranging (LIDAR) system that includes an optical source to transmit an optical beam and a drive circuit configured to drive a current through the optical source to transmit the optical beam at a frequency. The system also includes an operational amplifier comprising a plurality of inputs to produce an output voltage for receipt by the drive circuit as input to determine an amplitude of the current driven by the drive circuit through the light source. The system also includes electro optical circuitry coupled to a first input of the plurality of inputs to produce a phase locked loop to maintain the light at the frequency. The system also includes ramp control circuitry coupled to a second input the plurality of inputs to cause the output voltage of the operational amplifier to modulate the optical beam at the frequency.