Pixel Circuit Multi-Time Sampling for Wide Dynamic Range
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Solution Overview
Problem
Conventional Single Photon Avalanche Diode (SPAD) sensors face high power consumption due to numerous electronic avalanches, limiting their dynamic range and speed of electrical signal reading, while expanding the dynamic range increases pixel size and reduces reading speed.
Innovation Solution
A pixel circuit design with a photodiode, measuring circuit, and gate circuit that connects the photodiode and measuring circuit at multiple time points within a single recharge signal cycle, using multiple counters and switches to measure light intensity at different phases, allowing for separate count value output and summation to enhance sensitivity with reduced pixel size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SPAD sensors use high number of electronic avalanches to detect faint light, then detection sensitivity is improved, but power consumption increases
Solution Approach 1:
The pixel circuit is divided into multiple independent photodiodes (first photodiode, second photodiode, etc.) with different characteristics. Each photodiode handles different light intensity ranges, allowing the system to achieve high detection sensitivity across a wide dynamic range without requiring all photodiodes to operate at high avalanche multiplication levels simultaneously, thus reducing overall power consumption.
Solution Approach 2:
Different photodiodes are designed with different local qualities - specifically different breakdown voltages and avalanche multiplication characteristics. The first photodiode has higher breakdown voltage for faint light detection, while the second photodiode has lower breakdown voltage for brighter light. This allows each region to operate optimally for its intended light intensity range, improving sensitivity where needed while consuming less power overall.
2Adaptability or versatility
If conventional SPAD sensors expand dynamic range by increasing pixel size, then dynamic range is improved, but electrical signal reading speed decreases
Solution Approach 1:
Instead of using a single large photodiode to expand dynamic range, the invention segments the pixel into multiple smaller photodiodes. Each photodiode maintains small size for fast readout, while the combination of multiple photodiodes with different characteristics provides the expanded dynamic range. This resolves the contradiction by achieving wide dynamic range through parallel segmentation rather than serial enlargement.
Solution Approach 2:
The patent transitions from a single-dimensional approach (one large photodiode) to a multi-dimensional approach (multiple small photodiodes with different characteristics arranged in parallel). This dimensional change allows the system to achieve wide dynamic range without sacrificing readout speed, as each small photodiode can be read out quickly while the ensemble provides comprehensive light intensity coverage.
3Use of energy by moving object
If conventional SPAD sensors reduce power consumption by reducing avalanche multiplication, then power consumption is reduced, but dynamic range decreases
Solution Approach 1:
Different photodiodes are assigned different local qualities in terms of avalanche multiplication characteristics. The first photodiode operates with higher multiplication for faint light, while the second photodiode operates with lower multiplication for brighter light. This allows the system to reduce overall power consumption by not maximizing multiplication across all photodiodes, while still maintaining wide dynamic range through the diversity of local characteristics.
Solution Approach 2:
The photodetection function is segmented across multiple photodiodes with different operating characteristics. This segmentation allows the system to distribute the detection workload across devices operating at different power levels, reducing total power consumption while covering a wide dynamic range through the combined capabilities of the segmented photodiodes.
4Adaptability or versatility
If conventional SPAD sensors increase pixel size to expand dynamic range, then dynamic range is improved, but pixel circuit area increases
Solution Approach 1:
The pixel circuit is segmented into multiple smaller photodiodes arranged in parallel, each with different breakdown voltages. This segmentation allows the system to achieve wide dynamic range without increasing the overall pixel area, as the smaller individual photodiodes can be packed more efficiently than a single large photodiode would require.
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 design achieves a wider dynamic range with reduced power consumption, enabling high-speed electrical signal reading and smaller pixel size, while maintaining linear output characteristics and sensitivity.
Implementation Method 1
a photodiode; a measuring circuit configured to measure a light amount in accordance with a current output from one end of the photodiode
Implementation Method 2
In such an image sensor, a photon incident on the APD generates a photoelectric charge, which causes avalanche multiplication. Thus, it is possible to detect faint light.
Data Source
AI summary
Embodiments of the present disclosure provide example pixel circuits and image sensors. One example pixel circuit includes a photodiode, a measuring circuit that measures a light amount according to a current output from one end of the photodiode, and a gate circuit provided between the photodiode and the measuring circuit. The pixel circuit is supplied with a recharge signal to set one end of the photodiode to a predetermined potential. The gate circuit is configured to connect the photodiode and the measuring circuit such that the measuring circuit measures the light amount at a plurality of time points in a single cycle of the recharge signal.