Comparator Resistance Layout for Low-Voltage Image Sensor ADCs
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Solution Overview
Problem
The power consumption of AD conversion units in solid-state imaging devices is limited by the minimum voltage required for the comparator's operational components, such as the current source, differential input circuit, and current mirror circuit, making it difficult to reduce power consumption effectively.
Innovation Solution
The image sensor and photodetector incorporate a comparator with a differential input unit connected to capacitance units, a current mirror unit with resistance elements and transistor diodes, and a switch unit between the resistance elements and the transistor, allowing for reduced power source voltage by optimizing the voltage distribution across resistance elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a comparator with current source, differential input circuit, and current mirror circuit is used for AD conversion, then the AD conversion function is achieved, but the power consumption cannot be sufficiently reduced due to the minimum voltage requirement for normal operation
Solution Approach 1:
The comparator is divided into separate functional blocks: differential input unit, current mirror unit, and output unit. Each block can be independently optimized for voltage consumption. The resistance elements are segmented into multiple sections with different resistance values to distribute voltage drops appropriately across different circuit stages.
Solution Approach 2:
Different resistance values are assigned to different parts of the current mirror circuit based on local voltage requirements. The first resistance element has a different resistance value than the second resistance element, allowing optimal voltage distribution tailored to the specific needs of each circuit section.
2Use of energy by moving object
If the power source voltage of the comparator is reduced to lower power consumption, then energy efficiency improves, but the current source, differential input circuit, and current mirror circuit cannot operate normally
Solution Approach 1:
The resistance values of the resistance elements are specifically designed to change the voltage distribution parameters within the comparator. By adjusting resistance values, the voltage drops across different components are optimized to ensure minimum operating voltages are met even when the overall power source voltage is reduced.
Solution Approach 2:
The resistance elements act as intermediary components that mediate the voltage distribution between the power source and the active circuit components. They buffer and regulate voltage drops, ensuring that sensitive components like the differential input circuit and current mirror receive adequate voltage even when the supply voltage is reduced.
3Use of energy by moving object
If resistance elements are added to the comparator circuit to enable lower power source voltage, then power consumption is reduced, but the device complexity increases
Solution Approach 1:
The resistance elements are merged with the existing current mirror circuit structure rather than being added as separate external components. The first and second resistance elements are integrated into the current mirror unit, sharing circuit nodes and reducing overall component count despite the functional complexity.
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 a lower power source voltage for the comparator, thereby reducing the overall power consumption of the AD conversion unit and the image sensor.
Implementation Method 1
a pixel that includes a photoelectric conversion element
Data Source
AI summary
An object of the present technology is to provide an image sensor and a photodetector that are capable of reducing power consumption of an AD conversion unit. The image sensor includes a comparator, in which the comparator includes a differential input unit that includes a first input unit connected to a first capacitance unit and a second input unit connected to a second capacitance unit, a current mirror unit that includes a first resistance element connected to the differential input unit and an NMOS transistor diode-connected via the first resistance element, a second resistance element connected to the differential input unit, and a switch unit provided between the first input unit and a junction between the first resistance element and the NMOS transistor, and between the second input unit and a junction between the second resistance element and the current mirror unit.