Solid-State Imaging Device Differential Amplifier Circuit Noise Reduction
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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 noise ratio.
Innovation Solution
A solid-state imaging device is designed with a first and second vertical signal line, a current mirror circuit, and unit pixels and cells connected through a current supply line and constant current circuit, forming differential amplifier circuits to prevent current path elimination and reduce power supply voltage drop, thus maintaining current consumption and preventing prolonged settling time.
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 leading to increased noise ratio
Solution Approach 1:
The patent combines two unit pixels into a single differential amplifier circuit, merging their readout paths to share amplification resources. This reduces the number of independent amplification circuits needed, allowing for more compact pixel design while maintaining sufficient signal voltage through shared high-gain amplification.
Solution Approach 2:
The patent introduces dynamic control mechanisms including reset transistors and selection transistors that dynamically adjust the operating state of the differential amplifier circuit. These dynamic elements enable the circuit to switch between different operational modes (reset, signal readout, dummy signal readout) to optimize signal voltage output despite reduced individual pixel size.
2Device complexity
If current path is eliminated to simplify circuit structure, then device complexity is reduced, but settling time is prolonged
Solution Approach 1:
The patent implements preliminary reset actions through reset transistors that pre-charge or pre-discharge capacitive elements before signal readout. This preliminary action prepares the circuit in advance, ensuring that when the actual signal readout occurs, the settling time is minimized while maintaining a relatively simple circuit structure.
Solution Approach 2:
The patent maintains continuous current paths through the differential amplifier circuit even during non-signal periods by using dummy signal readout mechanisms. This continuity prevents complete current path elimination, ensuring that capacitive elements remain charged and the circuit maintains its operational state, thereby reducing settling time without significantly increasing structural complexity.
3Use of energy by moving object
If power supply voltage is reduced to lower power consumption, then energy efficiency is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent merges multiple pixel readout paths into a shared differential amplifier circuit, reducing the total number of amplification circuits required. This merging reduces overall power consumption while maintaining adequate signal-to-noise ratio through the high gain of the shared amplification circuit.
Solution Approach 2:
The patent employs parameter changes in the differential amplifier circuit design, including optimized transistor sizing, bias current adjustment, and capacitive element selection, to achieve optimal signal-to-noise ratio at reduced power consumption levels. By carefully tuning these parameters, the circuit maintains performance while consuming less power.
Data Source
AI summary
To suppress deterioration of image quality. A solid-state imaging device (1) according to an embodiment includes a first vertical signal line (VSL0k) and a second vertical signal line (VSL1k), a current mirror circuit (141) connected to the first and the second vertical signal lines, a first unit pixel (11i) connected to the first vertical signal line, a second unit pixel (11i+1) connected to the second vertical signal line, a first unit cell (11D0) connected to the first vertical signal line, a second unit cell (11D1) connected to the second vertical signal line, a current supply line (VCOM) connected to the first and the second unit pixels and the first and the second unit cells, and a constant current circuit (142) connected to the current supply line. A first amplification transistor of the first unit pixel, a second amplification transistor of the second unit pixel, the current mirror circuit, and the constant current circuit constitute a first differential amplifier circuit, and a third amplification transistor of the first unit cell, a fourth amplification transistor of the second unit cell, the current mirror circuit, and the constant current circuit constitute a second differential amplifier circuit.