Image Sensor Floating Diffusion Noise Sampling
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Solution Overview
Problem
Conventional three-dimensional image sensors face challenges in obtaining accurate depth information due to low sensitivity and signal-to-noise ratio (SNR) in depth pixels compared to color pixels.
Innovation Solution
The method involves illuminating an object with modulated transmission light and storing photo-charges in a storage region of depth pixels, sampling noise and demodulation voltages at specific times to enhance the signal-to-noise ratio by determining a valid voltage corresponding to the phase of the demodulation signal, which improves the accuracy of depth information measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If depth pixels are used to obtain depth information, then distance measurement capability is provided, but sensitivity and signal-to-noise ratio are low compared to color pixels
Solution Approach 1:
The patent applies preliminary action by sampling the noise voltage of the floating diffusion region before transferring the photo-charge from the storage region to the floating diffusion region. This allows the noise to be measured and subtracted from the subsequent signal voltage, effectively removing noise interference and improving the signal-to-noise ratio for depth pixel measurements.
Solution Approach 2:
The patent converts the harmful noise voltage into a useful measurement by sampling it separately and using it for noise removal. The noise voltage, which normally degrades measurement quality, is instead measured and subtracted from the signal voltage, transforming it from a harmful factor into a component that enables noise cancellation and improves measurement reliability.
2Measurement precision
If noise voltage is not removed, then device complexity is reduced, but depth information accuracy deteriorates due to noise interference
Solution Approach 1:
The patent implements preliminary action by performing noise voltage sampling before photo-charge transfer. This timing arrangement allows the noise to be captured and stored separately, then subtracted from the signal voltage in a subsequent calculation step, achieving noise removal without requiring additional hardware components.
Solution Approach 2:
The patent applies feedback by using the sampled noise voltage as a reference to correct the signal voltage measurement. The noise voltage obtained from the floating diffusion region is fed back into the calculation process and subtracted from the signal voltage, creating a closed-loop noise cancellation system that improves measurement accuracy.
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 effectively enhances the sensitivity and SNR of depth information acquisition, leading to more precise distance measurements by accurately determining the phase of the demodulation signal and reducing noise interference.
Implementation Method 1
a photo-charge is generated in a photo-detection region of the depth pixel by light reflected by the object
Data Source
AI summary
In a method of operating an image sensor, a noise voltage of a floating diffusion region is sampled after a reset voltage is applied to the floating diffusion region. A storage region, in which a photo-charge is stored, is electrically connected to the floating diffusion region after sampling the noise voltage, and a demodulation voltage of the floating diffusion region is sampled after the storage region and the floating diffusion region are electrically-connected. A voltage is determined based on the noise voltage and the demodulation voltage.