VCSEL Laser Drive Timing Adjustment for Pulse Accuracy
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Solution Overview
Problem
In laser drive devices for VCSELs, the timing of short-circuiting and turning off the light emitting element is delayed, leading to deviations in pulse light emission, which affects distance measurement accuracy due to variations in conditions such as temperature and power supply voltage.
Innovation Solution
A laser drive device with a timing adjustment unit that detects phase differences between drive and assist control signals, generating a timing adjustment signal to synchronize the assist and drive control signals, ensuring accurate pulse light emission by adjusting the delay times in both circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the assist circuit is added to short-circuit both ends of the light emitting element, then the fall time of the light emission driving current is shortened, but the timing deviation between drive control signal and assist control signal increases
Solution Approach 1:
The patent introduces a feedback mechanism where the timing adjustment unit continuously monitors the timing relationship between drive control signal and assist control signal, and automatically adjusts the phase of assist control signal to eliminate timing deviation. This closed-loop feedback ensures that the assist circuit operates in precise synchronization with the drive circuit, maintaining measurement accuracy while achieving fast fall time.
Solution Approach 2:
The timing adjustment unit acts as an intermediary between the drive circuit and assist circuit. It receives the drive control signal, generates the assist control signal with adjusted phase timing, and supplies it to the assist circuit. This intermediary component coordinates the operation of both circuits, ensuring that the assist circuit activates at the precise moment needed to shorten fall time without causing timing deviation.
2Device complexity
If the preceding stage transistors are made thinner using fine process, then the integration density is increased, but the control signal delay increases causing timing deviation
Solution Approach 1:
The timing adjustment unit dynamically adjusts the phase of the assist control signal based on the actual timing relationship with the drive control signal. This dynamic adjustment compensates for the variable delay introduced by the fine process transistors, maintaining precise timing synchronization despite the increased integration density achieved through thinner transistor structures.
3Reliability
If the assist control signal voltage is increased to improve signal integrity, then the signal robustness is enhanced, but the power consumption increases
Solution Approach 1:
The timing adjustment unit optimizes the voltage parameter of the assist control signal. Instead of using a fixed high voltage that would consume excessive power, the unit adjusts the voltage level dynamically based on the timing requirements and signal integrity needs, achieving reliable signal transmission with minimized power consumption.
Data Source
AI summary
The laser drive device (41) includes: a drive circuit (43) that drives a light emitting element (40) by a vertical cavity surface emitting laser to emit light on the basis of a drive control signal; an assist circuit (42) that short-circuits both ends of the light emitting element on the basis of an assist control signal to speed up a fall time of the light emitting element; a timing adjustment unit (20) that performs mutual timing adjustment between the drive control signal and the assist control signal on the basis of a timing adjustment signal; a phase detection unit (33) that detects a phase difference between the drive control signal and the assist control signal; and a timing control unit (34) that generates the timing adjustment signal on the basis of a phase difference detection result of the phase detection unit.