Shared Pixel Readout Structure for Compact Multi-Photodiode Sensing
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Solution Overview
Problem
Current image sensors face challenges in reducing the size and power consumption of pixel cells, particularly when incorporating multiple photodiodes, which affects the resolution and efficiency of imaging, especially in applications where space and power are limited, such as in mobile and wearable devices.
Innovation Solution
The implementation of a pixel cell design that includes a shared charge sensing unit, quantizer, and memory, where the controller manages the exposure periods and quantization operations for multiple photodiodes, allowing for concurrent or staggered operation to minimize footprint and power usage while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple photodiodes are incorporated in each pixel cell, then imaging resolution and functionality are improved, but pixel cell size increases
Solution Approach 1:
Multiple photodiodes (first photodiode for visible light, second photodiode for infrared light) are merged into a single pixel cell structure, sharing common readout circuitry including the charge sensing unit, quantizer, and memory. This integration allows multiple imaging functions within one compact pixel cell, improving resolution without proportionally increasing size.
Solution Approach 2:
The pixel cell is designed with multi-functional capability by incorporating both visible light and infrared light sensing in the same pixel cell. The shared readout structure serves multiple purposes: converting charge from different photodiodes, performing quantization operations, and storing digital outputs for different wavelength ranges, thereby achieving universal functionality within a compact design.
2Adaptability or versatility
If multiple photodiodes with separate readout circuitry are used, then imaging functionality is improved, but power consumption increases
Solution Approach 1:
The readout circuitry (charge sensing unit, quantizer, memory) is merged into a shared structure that serves multiple photodiodes. Instead of having separate complete readout chains for each photodiode, the patent combines them into one shared system, significantly reducing the number of circuit components and their associated power consumption while maintaining the ability to read out signals from multiple photodiodes.
Solution Approach 2:
The shared readout circuitry is designed with universal functionality to handle charge signals from different types of photodiodes (visible light and infrared). The charge sensing unit can convert charge from either photodiode, the quantizer can process signals from both, and the memory can store outputs from both, creating a multi-functional readout system that serves multiple purposes with a single circuit structure.
3Area of moving object
If a shared readout structure is used, then pixel cell size is reduced, but readout operation complexity increases
Solution Approach 1:
The shared readout structure employs dynamic control through the controller, which manages the timing and sequencing of readout operations for multiple photodiodes. The controller dynamically switches between different photodiodes and coordinates the charge sensing unit, quantizer, and memory operations in a time-multiplexed manner, allowing the same hardware to serve multiple functions through dynamic reconfiguration rather than requiring separate dedicated circuits for each photodiode.
Solution Approach 2:
The readout operation follows a periodic sequence where the controller alternates between reading out from the first photodiode and the second photodiode. The controller sets exposure periods for each photodiode, performs quantization operations in sequence, and stores digital outputs periodically. This periodic action pattern simplifies the control logic compared to simultaneous independent readout, as it uses regular time-multiplexed cycles to manage the shared resources.
4Reliability
If staggered exposure periods are implemented, then motion artifacts are reduced, but readout time increases
Solution Approach 1:
The controller implements preliminary action by setting the exposure period for the second photodiode to lag behind the first photodiode's exposure period. This staggered timing is pre-planned and coordinated so that while one photodiode is exposing, the other is reading out or preparing, optimizing the temporal sequence to minimize motion artifacts. The lagging exposure period is deliberately designed to align with the readout timing of the first photodiode, creating a smooth continuous operation.
Solution Approach 2:
The readout operation maintains continuity by overlapping the exposure and readout periods of different photodiodes. While the first photodiode is exposing during its exposure period, the second photodiode is already in its exposure period or preparing for readout. The controller continuously manages the sequence so that readout operations are continuously performed without idle gaps, utilizing the time when one photodiode is exposing to read out the other photodiode's data, thereby reducing total readout time despite staggered exposure.
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 enables collocated imaging for different light components, improves the fusion of 2D and 3D imaging data, reduces motion artifacts, and enhances spatial resolution, while reducing the size and power consumption of pixel cells, making them suitable for resource-constrained devices.
Implementation Method 1
A typical pixel in an image sensor includes a photodiode to sense incident light by converting photons into charge (e.g., electrons or holes)
Data Source
AI summary
An apparatus comprises a first photodiode, a second photodiode, a quantizer, a memory, and a controller configured to: set a first exposure period in which the first photodiode generates a first charge; set a second exposure period in which the second photodiode generates a second charge, the second exposure period being set based on the first exposure period and at least one of: a first time associated with a read out operation of the memory to a second apparatus, or a second time associated with a quantization operation by the quantizer; perform, using the quantizer, the first quantization operation of the first charge to generate a first digital output; and perform, using the quantizer, a second quantization operation of the second charge to generate a second digital output.