Amplifying Transistor Activation for Noise Reduction in Solid-State Imaging
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Solution Overview
Problem
Solid-state imaging apparatuses face issues with pseudo signals and fixed pattern noises due to the long-lasting variations in transistor bias, which degrade image quality and cause shading, especially when correlated double sampling is performed during periods of minute output variations from amplifying MOS transistors.
Innovation Solution
The apparatus and method involve maintaining amplifying transistors in an activation state for extended periods during readouts, allowing for sequential transfer of charges to a floating diffusion portion while controlling power source voltages to minimize pseudo signal occurrence, thereby reducing noise and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel pitch is decreased to increase the number of pixels, then the imaging resolution is improved, but the signal charge quantity of each photoelectric conversion element is reduced
Solution Approach 1:
Multiple photoelectric conversion elements share a common floating diffusion portion for charge accumulation and signal readout. This merging approach allows smaller pixels to maintain adequate signal charge quantity by pooling resources, resolving the contradiction between increased pixel count and maintained signal level.
2Speed
If correlated double sampling is performed during the period when the amplifying MOS transistor output is varying, then the readout speed is improved, but pseudo signals and fixed pattern noises are generated
Solution Approach 1:
The amplifying MOS transistor is activated and allowed to stabilize its output before the correlated double sampling readout begins. This preliminary stabilization action ensures that no pseudo signals or fixed pattern noises are generated during the measurement period, while still maintaining fast readout speed by preparing the transistor in advance.
3Use of energy by moving object
If the amplifying MOS transistor is switched off between readouts to reduce power consumption, then the power usage is reduced, but the transistor bias variation occurs affecting subsequent readouts
Solution Approach 1:
The amplifying MOS transistor is activated periodically only during the brief periods when readout is required, rather than remaining continuously on. This periodic activation reduces overall power consumption while the transistor is given sufficient time to stabilize before each activation period, maintaining bias stability. The system balances power savings with performance by using periodic rather than continuous operation.
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 reduces pseudo signals and fixed pattern noises, enhancing image quality by maintaining amplifying transistors in an active state during readouts, which extends the time period for noise output and signal output, thereby improving image quality and reducing shading effects.
Implementation Method 1
a plurality of photoelectric conversion elements each for generating an electric charge by a photoelectric conversion and for accumulating the electric charge
Data Source
AI summary
A solid state imaging apparatus of less fixed pattern noises and less shading comprises an imaging area wherein a plurality of pixel circuits are arranged in two dimensionally, and each of the pixel circuits includes a plurality of photoelectric conversion elements each for generating an electric charge by a photoelectric conversion and for accumulating the electric charge, a single floating diffusion portion for accumulating the charge, a plurality of transfer switches for transferring the electric charges respectively from the plurality of photoelectric conversion elements to the single floating diffusion portion and an amplifying transistor for amplifying a voltage corresponding to the electric charge accumulated by the floating diffusion portion, wherein the plurality of transfer switches transfers the electric charges from the plurality of photoelectric conversion elements sequentially to the floating diffusion portion while maintaining the amplifying transistors at the activation state.