Time-of-Flight Sensor Circuit with Pre-Biased Storage Transistors
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Solution Overview
Problem
Existing 3D image sensors face challenges in creating 3D images in real time due to the need for significant computer processing power and the use of larger pixel sizes to capture low-intensity, short-duration light, which results in poor signal-to-noise ratios and leakage currents.
Innovation Solution
A time-of-flight sensor design that includes a circuitry with storage transistors pre-biased with a negative voltage to minimize leakage current, allowing for longer charge storage and enabling smaller pixels to capture image signals over a longer period while maintaining an acceptable signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If larger pixel sizes are used to collect acceptable signal levels from low-intensity reflected light, then signal-to-noise ratio is improved, but device area and complexity increase
Solution Approach 1:
The storage transistor is pre-biased to a negative voltage before charge accumulation begins. This preliminary voltage application creates an electric field that repels minority carriers (electrons in p-type substrate) away from the storage region, preventing leakage current from draining accumulated charge during the integration period. This allows smaller pixels to maintain charge longer and achieve acceptable signal-to-noise ratios without requiring larger pixel areas.
2Quantity of substance
If multiple accumulations of light are performed to attain higher signal levels, then signal level is improved, but leakage current drains stored charge over time
Solution Approach 1:
The storage transistor is pre-biased to a negative voltage before charge accumulation begins. This preliminary voltage application creates an electric field that repels minority carriers (electrons in p-type substrate) away from the storage region, preventing leakage current from draining accumulated charge during the integration period. This allows smaller pixels to maintain charge longer and achieve acceptable signal-to-noise ratios without requiring larger pixel areas.
3Speed
If real-time 3D image acquisition is implemented using time of flight measurement, then imaging speed is improved, but processing power requirements increase
Solution Approach 1:
The patent replaces complex post-capture processing with an in-pixel modulation approach. By modulating the storage transistor gate voltage at the same frequency as the emitted light pulses, the system performs depth encoding directly in the sensor circuitry rather than requiring heavy computational processing after image capture. This substitution of mechanical/computational processing with electrical modulation in the sensor itself enables real-time 3D imaging with reduced processing power requirements.
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 design allows for efficient acquisition of time-of-flight and depth information with improved signal-to-noise ratios, enabling smaller pixel sizes and reduced processing power requirements for real-time 3D image capture.
Implementation Method 1
a sensor that detects the light that is reflected from the object
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
An apparatus includes a photodiode, a first and second storage transistor, a first and second transfer transistor, and a first and second output transistor. The first transfer transistor selectively transfers a first portion of the image charge from the photodiode to the first storage transistor for storing over multiple accumulation periods. The first output transistor selectively transfers a first sum of the first portion of the image charge to a readout node. The second transfer transistor selectively transfers a second portion of the image charge from the photodiode to the second storage transistor for storing over the multiple accumulation periods. The second output transistor selectively transfers a second sum of the second portion of the image charge to the readout node.