Solid-State Imaging Device Pixel Circuit Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As pixels have been further micronized, it has become difficult to obtain a signal voltage with sufficient voltage value from individual pixels, leading to increased noise components in the output voltage, which deteriorates image quality due to the increased ratio of noise components affecting the output image.
Innovation Solution
A solid-state imaging device is designed with a first and second vertical signal line, a current mirror circuit, and two unit pixels connected to these lines, along with a current supply line and a constant current circuit. Each unit pixel includes a photoelectric conversion element, transfer transistor, charge accumulation units, and an amplification transistor, allowing for switching between source follower and differential-type amplification read-out modes to adjust total capacitance and maintain low noise characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixels are further micronized to increase pixel density, then pixel integration density is improved, but signal voltage value deteriorates
Solution Approach 1:
The patent combines two unit pixels into a differential amplifier circuit, merging their charge accumulation units and amplification transistors to operate differentially. This merging allows the circuit to achieve higher signal voltage output by exploiting the differential amplification effect, thereby resolving the contradiction between pixel density and signal voltage value.
Solution Approach 2:
The patent introduces a switching transistor that dynamically switches between connecting the first charge accumulation unit and the second charge accumulation unit to the amplification transistor. This dynamic switching capability allows the circuit to adaptively adjust its operation mode, enabling seamless transition between source follower read-out and differential-type amplification read-out, thus maintaining optimal signal voltage across varying conditions.
2Measurement precision
If capacitance of charge accumulation unit is reduced to increase output voltage, then sensitivity is improved, but noise characteristic deteriorates
Solution Approach 1:
The patent changes the operational parameters of the charge accumulation unit by introducing a switching transistor that can dynamically alter the effective capacitance. By switching between different charge accumulation units with different capacitance values, the system can adjust the total capacitance to optimize the balance between output voltage and noise characteristic, resolving the contradiction between sensitivity and noise.
3Device complexity
If source follower read-out mode is used to simplify circuit, then device complexity is reduced, but noise suppression capability deteriorates
Solution Approach 1:
The patent designs the unit pixel circuit with multi-functionality, where the same circuit components (charge accumulation units, amplification transistors, switching transistors) can operate in multiple modes: source follower read-out mode for simple operations and differential-type amplification read-out mode for noise-sensitive applications. This universality allows the system to select the appropriate mode based on requirements, resolving the contradiction between circuit complexity and noise suppression capability.
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 enables the maximum number of electrons to be read out while maintaining low noise, allowing for seamless switching between read-out modes to suppress image quality deterioration.
Implementation Method 1
a photoelectric conversion element that photoelectrically converts incident light
Data Source
AI summary
A solid-state imaging device is disclosed. In one example, a solid-state imaging device includes a current mirror circuit connected to first and second vertical signal lines, first and second unit pixels connected to the first or the second vertical signal line, a current supply line connected to the first and the second unit pixels, and a constant current circuit connected to the current supply line. The unit pixels each include a photoelectric conversion element, a transfer transistor that transfers an electric charge generated in the photoelectric conversion element, first and second charge accumulation units that accumulate the transferred electric charge, a switching transistor configured to control accumulation of the electric charge by the second charge accumulation unit, and an amplification transistor that causes a voltage corresponding to electric charges accumulated the first and/or the second charge accumulation units to appear in the first or the second vertical signal line.