Switched Capacitor Amplifier for Solid-State Image Pickup Devices
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Solution Overview
Problem
Conventional CCD type image sensors face a trade-off between charge-voltage conversion efficiency and noise reduction, as reducing the detection capacitance to enhance efficiency increases thermal and 1/f noises, and enlarging the gate oxide capacitance to reduce noise decreases efficiency.
Innovation Solution
The implementation of a switched capacitor amplifier with a gate-grounded type inverting amplifier and a constant-current load transistor, allowing for independent selection of the amplification transistor size and reduction of feedback capacitance to improve charge-voltage conversion efficiency while minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the detection capacitance is reduced to improve charge-voltage conversion efficiency, then the conversion efficiency increases, but thermal and 1/f noises increase
Solution Approach 1:
The invention divides the amplification function into two separate stages: the detection diode handles charge-voltage conversion with minimal capacitance, while the subsequent amplifier stage handles signal amplification. This segmentation allows the detection diode to operate with low capacitance for high conversion efficiency without being burdened by the noise-generating large gate capacitance required for amplification, thus resolving the contradiction between conversion efficiency and noise reduction.
Solution Approach 2:
The invention introduces an intermediary capacitor connected between the detection diode and the amplifier input. This intermediary component acts as a buffer that isolates the detection diode from the amplifier's input capacitance, allowing the detection diode to maintain low capacitance for high conversion efficiency while the amplifier can have sufficient input capacitance for low noise operation without directly affecting the detection stage.
2Object-generated harmful factors
If the gate oxide capacitance is enlarged to reduce thermal and 1/f noises, then noise reduction is achieved, but charge-voltage conversion efficiency decreases
Solution Approach 1:
The invention separates the functions of charge-voltage conversion and signal amplification into distinct stages. The detection diode stage operates with minimal gate oxide capacitance to maximize conversion efficiency, while the separate amplifier stage uses larger gate oxide capacitance to minimize thermal and 1/f noises. This functional segmentation resolves the contradiction by allowing each stage to be optimized for its specific purpose without compromising the other.
Solution Approach 2:
The invention extracts the amplification function from the detection diode structure and places it in a separate amplifier circuit. By taking out the amplification requirement from the detection stage, the detection diode can be designed with minimal gate oxide capacitance for high conversion efficiency, while the extracted amplifier handles the noise reduction requirement independently, thus resolving the contradiction.
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 enables the achievement of high-quality images with reduced noise and increased resolution by decoupling charge-voltage conversion efficiency from detection capacitance, allowing for optimized design considerations for thermal and 1/f noises.
Implementation Method 1
a plurality of photoelectric conversion elements; a plurality of charge transfer elements for transferring photoelectric charge generated in the plurality of photoelectric conversion elements
Data Source
AI summary
A solid-state image pickup device includes a detection diode for detecting a transfer charge and a switched capacitor amplifier whose input section is connected to the detection diode. The switched capacitor amplifier includes an inverting amplifier, a reset transistor and a feedback capacitor which are connected between input and output sections of the inverting amplifier. Thus, the solid-state image pickup device satisfies the requirements for both improvement in charge-voltage conversion efficiency and reduction in generated noises.