Optical Sensor Readout Without Transfer Switch Settling Limits
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Solution Overview
Problem
Conventional optical sensors with a transfer switch between photodiodes and floating diffusions face limitations in frame rate speed due to settling periods and increased power consumption when propagating pixel driving pulses across the entire pixel region.
Innovation Solution
A signal readout method utilizing a light-receiving element with a completely depleted semiconductor junction and a potential curve with a negative slope towards the floating diffusion, connected to the uppermost position of the electronic potential well, along with a specific capacitance ratio between the light-receiving element and the floating diffusion, to enhance speed and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transfer switch is provided between photodiode and floating diffusion to enable high sensitivity and wide dynamic range, then light-receiving sensitivity is improved, but frame rate speed is restricted due to settling period requirements
Solution Approach 1:
The patent extracts and removes the transfer switch component from the pixel structure. By eliminating the transfer switch between the photodiode and floating diffusion, the settling period requirement is removed, enabling high-speed operation at 125 Mfps while maintaining high sensitivity through direct electrical connection for charge transfer.
2Reliability
If pixel driving pulses are propagated across the entire pixel region to control transfer switches, then charge transfer is enabled, but power consumption increases
Solution Approach 1:
The patent removes the transfer switch mechanism entirely, eliminating the need for pixel driving pulses to be propagated across the pixel region. The direct electrical connection between photodiode and floating diffusion enables passive charge transfer without active switching, dramatically reducing power consumption while maintaining reliable charge transfer efficiency.
3Reliability
If transfer switch settling period is extended to ensure complete charge transfer, then charge transfer completeness is improved, but frame rate is reduced
Solution Approach 1:
By extracting the transfer switch component, the patent eliminates the settling period bottleneck entirely. The direct electrical connection allows instantaneous charge transfer without the temporal constraints of switch settling, achieving both complete charge transfer and high frame rate of 125 Mfps simultaneously.
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
Enables higher-speed frame rates up to 125 Mfps while minimizing power consumption and maintaining high sensitivity, allowing for efficient signal readout with reduced noise and increased charge-voltage conversion gain.
Implementation Method 1
a light-receiving element with semiconductor junction completely depleted and a potential curve of electrons having a negative slope toward a floating diffusion
Implementation Method 2
a potential curve of electrons having a negative slope toward a floating diffusion and connected to an uppermost position of an electronic potential well
Data Source
AI summary
[Problem] To provide an optical sensor which can read out faster and requires lower power consumption than conventional optical sensors while maintaining advantages and superiorities of conventional optical sensors in which a transfer switch is provided between a light receiving element (PD) and a floating diffusion (CFD). [Solution] A semiconductor junction of a light-receiving element is fully depleted and a potential curve of electrons has a negative slope toward the floating diffusion and connected to an uppermost position of an electronic potential well of the floating g diffusion keeping its negative slope state.