SPAD Pixel Bias Feedback for Stable Light Detection
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Solution Overview
Problem
Existing light detecting devices using single-photon avalanche diodes (SPADs) face variations in excess bias due to temperature changes and variations in incident light, leading to decreased sensitivity and increased dark-current noise.
Innovation Solution
A solid state image sensor with a photoelectric conversion element having an anode and cathode connected to a predetermined node, an electric potential supply, a timing detection circuit, a sample and hold circuit, and a control section that controls the electric potential of another electrode based on the held potential, to stabilize the excess bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If monitor voltage is used to control anode electric potentials to suppress temperature-induced excess bias variation, then temperature stability is improved, but light-induced excess bias variation increases
Solution Approach 1:
The patent implements a feedback mechanism where the cathode electric potential is monitored and used to dynamically adjust the anode electric potential. The control section continuously monitors the cathode potential and adjusts the anode potential accordingly to maintain constant excess bias, creating a closed-loop control system that compensates for both temperature and light-induced variations.
Solution Approach 2:
The patent changes the control parameter from monitor voltage (cathode voltage) to directly controlling the anode electric potential based on cathode potential measurements. By adjusting the anode potential as the controlled parameter rather than using cathode potential as the control signal, the system achieves stable excess bias under varying light conditions.
2Measurement precision
If excess bias is increased to improve sensitivity, then detection sensitivity improves, but dark-current noise increases
Solution Approach 1:
The patent dynamically adjusts the excess bias parameter based on operating conditions rather than using a fixed high value. By controlling the anode electric potential to maintain constant excess bias, the system optimizes the balance between sensitivity and noise, avoiding the need to operate at consistently high excess bias levels that would increase dark current.
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 configuration effectively suppresses variations in excess bias caused by temperature and light changes, improving the sensitivity and accuracy of light detection.
Implementation Method 1
a photoelectric conversion element that includes an anode and a cathode
Implementation Method 2
a single-photon avalanche diode (SPAD) is used as a photoelectric conversion element
Data Source
AI summary
A light detecting device includes first pixel circuitry including a first avalanche photodiode, and second pixel circuitry including a second avalanche photodiode, a first delay circuit including an input coupled to a cathode of the second avalanche photodiode, a first circuit including a first input coupled to the cathode of the second avalanche photodiode, and a second input coupled to an output of the first delay circuit. The light detecting device includes a control circuit coupled to an output of the first circuit and configured to control a potential of an anode of the first avalanche photodiode based on the output of the first circuit. The control circuit is configured to control a potential of an anode of the second avalanche photodiode based on the output of the first circuit.