Amplifier Impedance Configuration for Image Sensor Black Level Stability
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Solution Overview
Problem
Conventional solid-state image sensing devices experience streaking due to uncontrolled current flow in amplifiers, leading to variations in black levels when high-intensity signals are processed, which affects the output image.
Innovation Solution
The design incorporates a power supply line with higher impedance than the ground line for each amplifier, using resistive elements to adjust the impedance ratio, ensuring that potential variations are minimized, thereby preventing streaking by increasing the IR drop on the power supply side and stabilizing the current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a simply structured source-grounded amplifier is used to suppress circuit area increase, then the circuit area is reduced, but the black level stability deteriorates when high-intensity signals are processed
Solution Approach 1:
The patent applies local quality by creating an asymmetric impedance configuration where the power supply line has higher impedance than the ground line. This local differentiation in impedance values at specific circuit nodes allows the amplifier to maintain black level stability while keeping the overall circuit structure simple and compact.
Solution Approach 2:
The patent changes the impedance parameter distribution in the power supply network by intentionally designing the power supply line impedance to be higher than the ground line impedance. This parameter change compensates for voltage drops and maintains stable operating conditions for the amplifier, preventing black level shifts during high-intensity signal processing.
2Device complexity
If amplifiers share common power supply and ground lines, then device complexity is reduced, but streaking occurs due to current variations affecting all amplifiers
Solution Approach 1:
The patent introduces local quality differences in the shared power supply network by assigning different impedance values to the power supply line and ground line. This local impedance differentiation ensures that current variations in one amplifier do not propagate equally to other amplifiers, thereby suppressing streaking while maintaining the simplicity of shared power supply lines.
Solution Approach 2:
The patent uses the impedance characteristics of the power supply line as an intermediary mechanism to isolate current variations between amplifiers. The higher impedance of the power supply line acts as a natural buffer that prevents current spikes from one amplifier from affecting the operating points of other amplifiers sharing the same power supply network.
3Power
If the current flowing into the current source changes due to large signal voltage, then power supply potential and ground potential change, but this causes threshold voltage variation and output potential instability
Solution Approach 1:
The patent changes the impedance parameters of the power supply network to compensate for the instability caused by large signal currents. By setting the power supply line impedance higher than the ground line impedance, the system maintains stable threshold voltages even when current flowing into the current source varies due to large input signal voltages.
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 suppresses streaking in output images by maintaining consistent black levels across the image, even when high-intensity signals are processed, by ensuring the impedance on the power supply side is greater than on the ground side, thus reducing the influence of high-intensity signals on other amplifiers.
Implementation Method 1
a pixel array in which pixels are arranged in rows and columns, each of the pixels converting light to an image signal
Implementation Method 2
with respect to each of the amplifiers, an impedance on a power supply side is greater than an impedance on a ground side
Data Source
AI summary
A solid-state image sensing device includes: a pixel array in which pixels performing photoelectric conversion are arranged in rows and columns; and a column amplification section in which an image signal output from each pixel is amplified. The column amplification section includes amplifiers each of which is provided for each column, and the column amplification section is connected to a power supply voltage feed section and the ground. An impedance on the power supply side of the amplifier is greater than an impedance on the ground side.