Avalanche Photodiode Rapid Charging for Shorter Dead Time
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Solution Overview
Problem
Conventional distance measuring systems using avalanche photodiodes face challenges in reducing distance measurement errors while shortening the dead time due to the need for high charging currents, which can lead to voltage fluctuations and erroneous detections.
Innovation Solution
A light detection device incorporating a rapid charging transistor with a thinner gate oxide film, a voltage limiting transistor, and a pulse generation unit to control charging currents, along with optional components like a forced quenching transistor and constant current source, to manage voltage levels and prevent erroneous detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the charging current is increased to shorten the dead time, then the dead time is shortened, but the distance measurement error increases
Solution Approach 1:
The patent changes the physical parameter of the gate oxide film thickness in the transistor structure. By using a transistor with a thinner gate oxide film, the transistor achieves lower on-resistance, which allows rapid charging of the photodiode with reduced voltage drop, thereby shortening dead time without increasing distance measurement error
Solution Approach 2:
The patent applies different gate oxide film thicknesses to different transistors within the circuit. Specifically, the rapid charging transistor has a thinner gate oxide film compared to other transistors, optimizing its performance for rapid charging while other transistors maintain thicker films for stability and voltage limiting functions
2Measurement precision
If the charging current is reduced to reduce the distance measurement error, then the distance measurement error is reduced, but the dead time is lengthened
Solution Approach 1:
The patent modifies the transistor's gate oxide film thickness parameter to achieve lower on-resistance. This allows the system to use reduced charging current while still achieving rapid charging speed, thereby reducing distance measurement error without lengthening dead time
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 effectively shortens the dead time and reduces distance measurement errors by managing charging currents and preventing voltage fluctuations, thereby enhancing the accuracy and efficiency of distance measurements.
Implementation Method 1
a light receiving element that performs avalanche multiplication
Implementation Method 2
a rapid charging transistor in which a film thickness of a gate oxide film is less than that of the voltage limiting transistor and that supplies a charging current to the avalanche photodiode
Data Source
AI summary
In a light detection device and a distance measuring system that obtain a distance from a round-trip time of light, a distance measurement error is reduced while a dead time is shortened. A logic gate outputs an output signal on the basis of a result of comparison between an input voltage depending on a voltage of one terminal of the cathode or the anode of an avalanche photodiode and a predetermined threshold voltage. A voltage limiting transistor limits the input voltage. A rapid charging transistor, in which a film thickness of a gate oxide film is less than that of the voltage limiting transistor, supplies a charging current to the avalanche photodiode in accordance with a predetermined pulse signal. A pulse generation unit generates the pulse signal on the basis of the output signal and supplies the pulse signal to the rapid charging transistor.