Solid-State Image Sensor Avalanche Photodiode Bias Control
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Solution Overview
Problem
Conventional solid-state image sensors with avalanche photodiodes face increased power consumption due to dark current generated by crystal defects, leading to unnecessary avalanche multiplication even in the absence of photons.
Innovation Solution
The implementation of a solid-state image sensor design that selectively applies a reverse bias voltage greater than or equal to the breakdown voltage only to normal pixels during image capture, while setting abnormal pixels to operate in a linear mode to prevent avalanche multiplication, thereby reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reverse bias voltage greater than breakdown voltage is applied to avalanche photodiode to enable single photon detection, then photon detection capability is improved, but power consumption increases due to dark current and unnecessary avalanche multiplication
Solution Approach 1:
The patent applies a reverse bias voltage greater than or equal to the breakdown voltage only during the readout period after exposure, rather than continuously during the entire imaging cycle. The voltage is switched between a high voltage state (for photon detection and signal readout) and a low voltage state (during integration/exposure). This temporal parameter change allows the avalanche photodiode to maintain photon detection capability when needed while minimizing power consumption during periods when detection is not active, thereby resolving the contradiction between measurement precision and energy use.
2Reliability
If crystal defect exists in avalanche photodiode, then dark current is generated causing unnecessary avalanche multiplication, but this leads to increased power consumption and reduced detection accuracy
Solution Approach 1:
The patent implements periodic switching of the reverse bias voltage applied to the avalanche photodiode. During the exposure/integration period, a lower voltage is applied to minimize dark current and power consumption. During the subsequent readout period, the voltage is increased to the breakdown level to enable accurate detection of accumulated photons. This periodic action pattern allows the system to maintain detection accuracy while significantly reducing power consumption compared to continuous high-voltage operation, effectively addressing the issue of dark current from crystal defects.
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 approach effectively suppresses power consumption by preventing avalanche multiplication in abnormal pixels and allows for accurate identification and correction of defective pixels, enhancing the overall efficiency of the image capturing process.
Implementation Method 1
When a photon is incident on an avalanche photodiode across which a reverse bias voltage greater than a breakdown voltage is applied, a carrier is generated, avalanche multiplication occurs, and a large electric current flows
Implementation Method 2
a carrier is generated, avalanche multiplication occurs, and a large electric current flows
Data Source
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AI summary
A solid-state image sensor comprises: a pixel portion in which a plurality of pixels are arranged, each pixel being provided with a sensor that includes an avalanche photodiode and a quenching resistor; and setting means configured to perform setting so that a bias voltage greater than or equal to a breakdown voltage of the avalanche photodiodes is applied across the avalanche photodiodes provided in normal pixels among the plurality of pixels, and a bias voltage smaller than the breakdown voltage of the avalanche photodiodes is applied across the avalanche photodiode provided in an abnormal pixel among the plurality of pixels.