SPAD Photodetection Device with Dead-Time Correction
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Solution Overview
Problem
Photodetection devices experience variations in dead time among pixels due to manufacturing variations, leading to inconsistent sensitivity characteristics under high illuminance conditions, resulting in photo response non-uniformity (PRNU) and inaccurate photon counting.
Innovation Solution
A photodetection device with a plurality of pixels, each equipped with an optical response unit, pulse detection unit, counter, dynamic separation switch, and input fixing unit, along with a correction circuit and memory to store correction values, dynamically separates electrical connections and corrects count values using calculated dead times and environmental correction coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodetection device uses SPAD pixels to detect photons, then it achieves high sensitivity for distance measurement, but manufacturing variations cause dead time variations among pixels leading to photo response non-uniformity (PRNU) under high illuminance
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the input voltage of the pulse detection unit to a specific potential (ground potential) that ensures the input transistor remains turned on. This voltage parameter adjustment compensates for dead time variations among pixels, thereby reducing PRNU and improving photo response uniformity under high illuminance conditions while maintaining high photon counting accuracy
Solution Approach 2:
The patent implements feedback through a correction circuit that uses stored correction values (dead time characteristics) for each pixel to correct the count values. The system measures dead time for each pixel, stores these characteristics, and applies them as correction factors during photon counting operations, creating a closed-loop feedback mechanism that eliminates the impact of manufacturing variations on measurement precision
2Productivity
If the photodetection device operates under high illuminance conditions, then it can detect more photons for faster measurement, but dead time variations cause count loss variations deteriorating sensitivity characteristics
Solution Approach 1:
The patent changes the operating voltage parameter of the pulse detection unit to ground potential, ensuring the input transistor remains in a consistently turned-on state. This parameter adjustment maintains linear response characteristics even under high photon flux conditions, preventing count loss variations and preserving measurement precision while enabling high-speed photon detection
Solution Approach 2:
The patent performs preliminary characterization of each pixel's dead time and stores correction values before actual photon counting operations. By pre-measuring and storing dead time characteristics, the system prepares correction factors in advance that will be applied during high-speed operation, eliminating the need for real-time adjustments and maintaining precision during high-productivity operations
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 improves sensitivity characteristics by accurately counting photons even under high illuminance conditions, reducing variations in dead time and enhancing photo response uniformity.
Implementation Method 1
an optical response unit that reacts to the photons
Implementation Method 2
an avalanche phenomenon occurs due to incidence of a single photon. The APD that multiplies a single photon by the avalanche phenomenon is called a single photon avalanche diode (SPAD)
Data Source
AI summary
To provide a photodetection device capable of improving sensitivity characteristics under an environment of high illuminance.A photodetection device according to the present disclosure includes: a plurality of pixels that counts the number of photons included in incident light; a memory that stores a correction value used to correct a count value by each of the plurality of pixels; and a correction circuit that corrects the count value by using the correction value. In the photodetection device, the plurality of pixels includes: an optical response unit that reacts to the photons; a pulse detection unit that includes an input transistor to which a result of reaction of the optical response unit is input and detects a pulse indicating the result of reaction; a counter that measures the count value on the basis of the pulse; a dynamic separation switch unit that dynamically separates electrical connection between the optical response unit and the pulse detection unit; and an input fixing unit that temporarily fixes an input voltage of the pulse detection unit to a potential at which the input transistor is turned on.