Photodiode Readout Capacitance Noise Correction for 3D Depth Sensing
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Solution Overview
Problem
3D measuring systems using CMOS image sensors face challenges with noise interference from reset processes and background light, which degrade the signal-to-noise ratio and accuracy of depth measurements.
Innovation Solution
An optical detection device with a photodiode structure and readout capacitance that separates noise contributions by reading out charge values during both accumulation and transfer phases, allowing for noise correction and reduced reset noise impact, while also efficiently handling background light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If reset processes are performed frequently to handle background light interference, then background light rejection improves, but reset noise increases and degrades signal-to-noise ratio
Solution Approach 1:
The patent segments the charge accumulation and readout processes into distinct phases (first accumulation phase, transfer phase, second accumulation phase) with separate readout operations. By reading out charge values at different stages and differentiating between them, the system can identify and eliminate reset noise contributions while maintaining background light rejection, thus resolving the contradiction between reducing background light interference and maintaining signal-to-noise ratio.
Solution Approach 2:
The patent implements a feedback mechanism where the first readout value (containing reset noise) is used to correct the second readout value. The control means subtracts the first readout value from the second readout value to obtain a corrected charge value, effectively using the measured reset noise as feedback to eliminate its impact on the final measurement, thereby maintaining high signal-to-noise ratio while handling background light.
2Measurement precision
If exposure time is extended to improve depth measurement accuracy, then measurement precision improves, but noise accumulation increases
Solution Approach 1:
The patent employs periodic action by using alternating accumulation phases followed by transfer phases. Charge is accumulated during illumination periods, then transferred to storage, allowing periodic reset and readout operations. This periodic cycle enables extended effective integration time for improved depth accuracy while periodically eliminating accumulated noise through the reset and differential readout process.
Solution Approach 2:
The patent performs preliminary action by conducting the first readout during the first accumulation phase to measure reset noise before the actual depth measurement is completed. This preliminary measurement of noise characteristics allows for subsequent correction of the final depth measurement, enabling extended exposure for better accuracy without suffering from uncorrected noise accumulation.
3Object-affected harmful factors
If reset frequency is increased to reduce background light impact, then background light rejection improves, but device complexity and operation complexity increase
Solution Approach 1:
The patent merges multiple functions into the dual-readout process: background light rejection, reset noise measurement, and reset noise correction are all accomplished through the same first and second readout operations. By combining these functions into a unified readout sequence rather than requiring separate operations for each function, the patent reduces overall device and operational complexity while maintaining effective background light rejection.
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 enhances the signal-to-noise ratio and improves the accuracy of depth measurements by minimizing noise contributions and correcting for background light, enabling more precise 3D data acquisition without the need for frequent reset processes.
Implementation Method 1
a photodiode capacitance for accumulating charge carriers from electromagnetic radiation
Data Source
AI summary
The central idea of the present invention is that a readout result of an optical detection unit which is based on accumulating photocharges can be improved when the charge carriers accumulated on a photodiode capacitance can be transferred to a readout capacitance before being read out by a readout unit, and when the state of the readout capacitance can be read out in a non-destructive manner by the readout unit, so that a noise portion in the readout signal can be corrected by reading out the readout capacitance during charge accumulation and again reading out the readout capacitance after the end of charge accumulation. Additionally, it becomes possible by the transfer to the readout capacitance to vary the sensitivity of the optical detection device within broad limits and to record a sequence of successive light pulses, without having to reset a photodiode before recording every single light pulse.