Pixel Sensor Element Noise Reduction via Segmented AD Conversion
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Solution Overview
Problem
Solid-state imaging apparatuses face noise issues due to area constraints and small currents, particularly in subthreshold currents, which affect the accuracy and quality of signal readout.
Innovation Solution
Incorporating a comparing unit, a band limiting unit, and an amplification unit to compare detection signals with reference signals, narrow signal bands, and amplify the band-limited signals, thereby reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If analog to digital conversion is performed within a limited area using integrating AD conversion scheme, then area efficiency is improved, but noise increases due to small area and small current
Solution Approach 1:
The AD conversion process is divided into two stages: a coarse AD conversion stage using integrating AD conversion scheme for area efficiency, and a fine AD conversion stage using correlation double sampling for noise reduction. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between area efficiency and noise performance
Solution Approach 2:
Coarse AD conversion is performed first as a preliminary action to reduce the dynamic range of the signal before the final fine AD conversion. This preliminary processing reduces the burden on the second stage and allows for more effective noise filtering while maintaining area efficiency
2Adaptability or versatility
If lamination technology is applied to bond multiple layers of wafers, then integration capability is improved, but noise increases due to small area constraints
Solution Approach 1:
The imaging apparatus is divided into multiple functional layers (first imaging unit with light receiving elements, second imaging unit with correlation double sampling circuitry) that are laminated together. Each layer performs a specific function, allowing high integration capability while the distributed architecture reduces noise by spreading the conversion process across multiple locations and time steps
3Use of energy by moving object
If subthreshold current is used for AD conversion, then power consumption is reduced, but noise increases due to small current magnitude
Solution Approach 1:
The AD conversion process is segmented into coarse and fine stages, where the coarse stage uses subthreshold current for low power consumption, and the fine stage uses correlation double sampling to filter noise. This segmentation allows the system to benefit from both low power consumption and noise reduction
Solution Approach 2:
Correlation double sampling uses feedback mechanisms to subtract noise from the signal by measuring and eliminating noise components in the fine AD conversion stage, allowing subthreshold current operation while maintaining signal quality
Data Source
AI summary
The present disclosure relates to a sensor element and an electronic device that can further reduce noise.In a solid-state imaging apparatus that performs AD conversion in a pixel, a comparator circuit included in the pixel at least has: a comparing unit that compares a pixel signal output from a pixel circuit with a reference signal which is a slope signal whose level monotonously decreases with time; a band limiting unit that performs band limiting by narrowing a band of a signal that changes according to a result of comparison by the comparing unit; and an amplification unit that amplifies the signal whose band has been limited through the band limiting unit. The present technology can be applied to a solid-state imaging apparatus that performs AD conversion in a pixel, for example.