CMOS Image Sensor Log Compression for Wide Dynamic Range
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Solution Overview
Problem
Current CMOS image sensors face limitations in achieving a high dynamic range for improved image quality, as they struggle to effectively handle and convert the wide range of light signals into output signals.
Innovation Solution
A solid-state imaging device is designed with a photoelectric conversion unit, a transfer unit, an amplifier unit, and a logarithmic compression conversion unit, where charges are converted into voltages using a diode operational in the sub-threshold region, allowing for the extraction of a wide range of light signals through logarithmic compression and charge-to-voltage conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional charge-to-voltage conversion is used in CMOS image sensors, then the circuit structure is simple, but the dynamic range of the output signal is limited
Solution Approach 1:
The patent segments the charge-to-voltage conversion process into two distinct paths: a logarithmic compression conversion unit for handling overflow currents with logarithmic characteristics, and a conventional charge-to-voltage conversion unit for linear charge conversion. This segmentation allows each unit to be optimized for its specific function, achieving wide dynamic range while maintaining reasonable circuit complexity through specialized functional division.
2Quantity of substance
If the amount of charges in a pixel unit is increased to achieve wide dynamic range, then the dynamic range improves, but the circuit complexity and processing difficulty increase
Solution Approach 1:
The patent introduces a transfer unit as an intermediary component that selectively connects the photoelectric conversion unit to either the logarithmic compression conversion unit or the conventional charge-to-voltage conversion unit. This intermediary mechanism enables flexible routing of charges based on their magnitude, allowing the system to process large amounts of charges through the appropriate conversion path without overwhelming the overall circuit complexity.
3Quantity of substance
If logarithmic compression conversion is implemented, then the dynamic range of light signals can be extracted, but the circuit configuration becomes more complex
Solution Approach 1:
The patent merges the logarithmic compression conversion unit and the conventional charge-to-voltage conversion unit into a single integrated circuit architecture, with both units sharing common components such as the transfer unit, amplifier unit, and output unit. This merging approach allows the system to handle both logarithmic and linear conversion modes within a unified structure, reducing overall complexity compared to having completely separate systems.
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 the acquisition of high-quality images with a wide dynamic range by effectively handling overflow currents, enhancing the concurrency of logarithmic compression and linear signals, thereby improving image quality.
Implementation Method 1
a photoelectric conversion unit that generates charges by photoelectric conversion
Implementation Method 2
a logarithmic compression conversion unit connected to the input node, wherein when a current generated by charges overflowing from the photoelectric conversion unit to the input node with the transfer unit being not conductive is converted into a voltage corresponding to the current by logarithmic compression performed by the logarithmic compression conversion unit
Data Source
AI summary
A method of driving a solid-state imaging device includes: setting voltage of an input node of an amplifier unit to a first voltage by using logarithmic compression to convert current generated by charges overflowing from a photoelectric conversion unit to the input node into voltage corresponding to the current, transferring charges from the photoelectric conversion unit to the input node, setting voltage of the input node to a second voltage by converting the charges into voltage corresponding to the charges, at the amplifier unit, outputting a first signal based on the first voltage and a second signal based on the second voltage, performing the logarithmic compression by using a diode connected to the input node, and acquiring, as a reference signal, an output of the amplifier unit when the input node is set to a third voltage defined in accordance with a threshold voltage of the diode.