Ambient Light Sensor SAR Readout Without Transimpedance Amplifiers
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Solution Overview
Problem
Existing ambient light sensors face inefficiencies in the analog-to-digital conversion process, particularly in terms of bulkiness and the need for transimpedance amplifiers.
Innovation Solution
The ambient light sensor design incorporates a successive approximation analog-to-digital converter that utilizes the capacitances of readout regions of pixels, eliminating the need for transimpedance amplifiers and reducing bulkiness by implementing capacitive elements without separate capacitors, with control circuits managing transfer gates and switches to optimize conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional analog-to-digital converter with transimpedance amplifiers is used, then conversion accuracy is maintained, but the sensor becomes bulkier and more complex
Solution Approach 1:
The patent merges the readout region of each pixel with the capacitive element of the analog-to-digital converter. The readout region serves dual purposes: collecting photogenerated charges and functioning as the storage capacitor for the converter. This eliminates the need for separate capacitor structures and transimpedance amplifiers, thereby reducing sensor area and device complexity while maintaining conversion functionality
Solution Approach 2:
The readout region is designed to perform multiple functions simultaneously: it acts as both the charge collection node for the photodiode and the capacitive element for the analog-to-digital conversion process. This multi-functionality eliminates redundant components and reduces the overall sensor structure without compromising conversion accuracy
2Area of stationary object
If transimpedance amplifiers are included in the converter, then conversion precision is improved, but the sensor area increases
Solution Approach 1:
The patent eliminates transimpedance amplifiers by directly using the readout region capacitance for the conversion process. The capacitive coupling between the photodiode and readout region provides the necessary signal transformation without requiring additional amplifier circuits, thereby reducing sensor area while maintaining adequate conversion precision through the successive approximation method
3Volume of moving object
If separate capacitors are added for the analog-to-digital converter, then conversion functionality is enhanced, but the sensor becomes more bulky
Solution Approach 1:
The patent combines the readout region with the capacitive storage function, eliminating the need for separate capacitor structures. The readout region's inherent capacitance is utilized directly in the analog-to-digital conversion process, maintaining conversion efficiency while significantly reducing the sensor's overall volume and structure complexity
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 efficient analog-to-digital conversion without the need for transimpedance amplifiers, resulting in a less bulky sensor that effectively processes ambient light data, suitable for integration in electronic devices like OLED screens.
Implementation Method 1
Each pixel comprises: a pinned photodiode arranged in a first doped insulated well
Data Source
AI summary
An ambient light sensor includes pixels arranged in an array. Each pixel includes a doped insulated well of a first type, a pinned photodiode in the well, a doped region of a second type arranged in the well, a transfer gate coupling the photodiode to said region, and a first circuit applying a first or second potential to the well. A successive approximation analog-to-digital converter of the sensor has a node connected to the doped regions of the pixels, a switch applying a third potential to the node, a comparator coupled to the node, and a second circuit receiving an output of the comparator and controlling the first circuits to selectively apply the first and second potentials. A sensor control circuit controls the gates and the first switch.