Solid-State Imaging Element Dual Sample Hold Circuits
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Solution Overview
Problem
Conventional solid-state imaging elements using indirect ToF systems suffer from signal leakage due to charge holding in the gate capacity, leading to deteriorated PLS properties and insufficient dynamic range, which negatively impact image quality, particularly in depth mapping applications.
Innovation Solution
The implementation of a solid-state imaging element with dual sample hold circuits for each pixel, each holding a distinct pixel signal, along with a vertical scanning circuit for simultaneous exposure and signal output, and an exposure time control mechanism to optimize image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charge is held in the gate capacity to reduce read noise, then read noise is reduced, but signal leakage occurs during exposure buildup which deteriorates PLS properties
Solution Approach 1:
The patent extracts the charge holding function from the gate capacity and relocates it to a dedicated sample hold circuit. This separation removes the harmful signal leakage effect from the pixel while preserving the useful charge holding capability, thereby resolving the contradiction between read noise reduction and PLS property maintenance.
Solution Approach 2:
The sample hold circuit acts as an intermediary between the pixel and the readout circuitry. It temporarily stores the pixel signal without causing signal leakage, enabling noise reduction while protecting PLS properties. The intermediary structure isolates the harmful effects from the original system.
2Reliability
If gate capacity is used to hold charge, then read noise is reduced, but saturation charge amount is rate-determined by gate capacity causing insufficient dynamic range
Solution Approach 1:
The charge holding capacity is extracted from the gate and placed in a separate sample hold circuit with independently adjustable capacitance. This allows the dynamic range to be optimized without being constrained by the gate's fixed capacity requirements for noise reduction.
Solution Approach 2:
The patent changes the parameter of charge storage capacity by using a separately designed sample hold circuit with adjustable capacitance values. This enables independent optimization of both read noise (through proper holding) and dynamic range (through sufficient capacitance), resolving the contradiction between these two parameters.
3Manufacturing precision
If dual sample hold circuits are implemented for each pixel, then image quality is improved with extended dynamic range, but circuit complexity increases
Solution Approach 1:
The sample hold circuit is designed to perform multiple functions: charge holding, signal buffering, and dynamic range extension. By making the circuit multi-functional, the patent reduces the need for separate dedicated circuits for each function, thereby managing complexity while achieving improved image quality.
Solution Approach 2:
The sample hold circuit performs preliminary signal preparation and holding before the main readout process. This preliminary action simplifies subsequent processing stages and allows for optimized circuit design in later stages, balancing overall system complexity with performance benefits.
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 configuration enhances image quality by improving PLS properties and extending the dynamic range, resulting in better depth map images with reduced noise and improved reading speed.
Implementation Method 1
a photoelectric conversion element that converts received light into charge
Data Source
AI summary
To improve image quality in a solid-state imaging element using an indirect ToF system.The solid-state imaging element includes a pixel signal generation unit, a first sample hold circuit, and a second sample hold circuit. The pixel signal generation unit generates a first pixel signal corresponding to an amount of charge transferred from a photoelectric conversion element to a first floating diffusion layer and a second pixel signal corresponding to an amount of charge transferred from the photoelectric conversion element to a second floating diffusion layer. The first sample hold circuit holds the first pixel signal. The second sample hold circuit holds the second pixel signal.