SPAD Pixel Quenching Circuit for Accurate Distance Imaging
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Solution Overview
Problem
Existing imaging technologies using SPADs suffer from after-pulse generation and latching current issues, leading to prolonged dead times and reduced accuracy in distance measurement.
Innovation Solution
A light detecting device array is implemented, utilizing a transistor as a quenching resistance to control cathode potential and incorporate a switch to manage current flow, preventing after-pulse generation and latching current effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitance is connected with the SPAD during the refresh period to suppress after-pulse generation, then after-pulse generation is suppressed, but the dead time is prolonged and measurement precision deteriorates
Solution Approach 1:
The quenching circuit is activated immediately upon detecting an avalanche multiplication signal, before any after-pulse can occur. This preliminary action prevents after-pulse generation without requiring the SPAD to be disconnected or placed in a floating state, thus avoiding dead time extension while maintaining measurement precision.
Solution Approach 2:
The harmful quenching current is extracted and directed through a dedicated quenching circuit that is separate from the main signal path. This allows the SPAD to return to its normal operating state quickly without interference, preventing both after-pulses and dead time extension while maintaining measurement accuracy.
2Reliability
If the SPAD is disconnected from the power source during the detection period to suppress after-pulse generation, then after-pulse generation is suppressed, but the dead time is prolonged
Solution Approach 1:
The quenching circuit uses the avalanche multiplication current itself to generate the quenching effect. The circuit automatically activates when a photon is detected, uses the existing current to suppress after-pulses, and then automatically deactivates without requiring external control signals or disconnection from the power source, thus eliminating dead time extension.
3Reliability
If a quenching resistance is used to control current flow after avalanche multiplication, then avalanche multiplication is suppressed, but the current may fail to drop below latching current, prolonging dead time
Solution Approach 1:
The quenching circuit dynamically changes the resistance value based on the detection state. During normal operation, the quenching resistance is high to allow normal current flow. Upon detecting an avalanche multiplication signal, the circuit switches to a low resistance state to provide strong quenching current, ensuring the current drops below the latching current level and preventing dead time extension.
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 prevents prolonged dead times, enhancing the accuracy of distance measurement by minimizing after-pulse and latching current impacts.
Implementation Method 1
With the SPAD, there sometimes occurs what is known as an after-pulse phenomenon in which some of the carriers (electrons and holes) generated by avalanche multiplication are trapped by impurity levels
Implementation Method 2
When a photon enters the SPAD during the detection period to generate avalanche multiplication
Implementation Method 3
the SPAD and a capacitance for biasing it are connected with a power source during a refresh period
Data Source
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AI summary
This technology relates to an imaging apparatus and an imaging system for improving the accuracy of distance measurement performed by use of SPADs. The imaging apparatus includes a pixel array section having pixel sections arrayed therein. Each pixel section includes: an SPAD (single photon avalanche photodiode); a resistance component configured to be connected serially with the SPAD; an output section configured to output a light reception signal indicating photon incidence on the SPAD; and a pulse generation section configured to output a pulse signal in synchronism with the output of the light reception signal. Each pixel sections further includes at least one of: a switch configured to be connected interposingly between the SPAD and the resistance component and turned off in synchronism with the pulse signal; or a pull-in section configured to pull in an input current flowing through the SPAD via the resistance component in synchronism with the pulse signal, thereby suppressing the input current flowing through the SPAD. This technology may be applied to cameras that capture range images, for example.