Solid-State Imaging Column AD Conversion with Switchable Frequency Band
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Solution Overview
Problem
Conventional solid-state imaging devices fail to effectively suppress noise-induced image quality deterioration due to the lack of consideration for correlated sampling and frequency band switching, leading to unresolved issues with fixed pattern noise and random noise.
Innovation Solution
A solid-state imaging device with a column AD conversion unit that includes a comparison unit and an up-down counting unit, capable of switching frequency band characteristics, allowing for the same reference signal voltage to be used across columns and enabling correlated sampling to cancel noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frequency band characteristics are switched to suppress random noise, then noise suppression is improved, but device complexity increases
Solution Approach 1:
The comparison unit dynamically switches between wideband and narrowband frequency characteristics based on signal conditions. This is achieved through a switchable filter structure that adjusts bandwidth in real-time, allowing the system to optimize noise suppression while maintaining operational flexibility and avoiding permanent complexity increases.
Solution Approach 2:
The system changes the frequency band parameter of the comparison unit adaptively. By modifying the bandwidth parameter from wide to narrow based on signal-to-noise conditions, the system achieves effective random noise suppression without requiring multiple fixed-configuration comparison units, thereby controlling device complexity.
2Object-affected harmful factors
If the same reference signal voltage is used across columns for correlated sampling, then noise cancellation is improved, but conversion gain homogeneity becomes difficult to maintain
Solution Approach 1:
The system implements feedback mechanisms to monitor and adjust conversion gains across columns when using the same reference signal voltage for correlated sampling. This feedback allows the system to maintain gain homogeneity while benefiting from the noise cancellation advantages of correlated sampling with a common reference signal.
Solution Approach 2:
The invention uses the same reference signal voltage across all columns to achieve homogeneous sampling conditions, which enables effective correlated sampling for fixed pattern noise cancellation. This homogeneity in reference signal application is the key to achieving uniform noise suppression across the entire pixel array.
3Object-affected harmful factors
If narrow band characteristics are used during counting periods, then random noise is suppressed, but AD conversion speed decreases
Solution Approach 1:
The comparison unit alternates between wideband and narrowband modes in periodic fashion, switching to narrowband only during active counting periods when noise suppression is critical, and using wideband during other periods for faster operation. This periodic switching optimizes both noise suppression and conversion speed.
Solution Approach 2:
The system dynamically adjusts the bandwidth of the comparison unit based on the operational phase. During counting periods when precision is critical, narrowband filtering is applied to suppress noise. During other phases, wideband characteristics are used to maintain high conversion speed, achieving optimal performance across different operational states.
Data Source
AI summary
A solid-state imaging device includes the following. Pixels arranged in matrix converts received light into signal voltage. A column AD conversion unit, which includes a comparison unit and an up-down counting unit, converts signal voltage to digital signal. The comparison unit compares a value of signal voltage to a gradually changing value of reference signal voltage. The up-down counting unit counts, by one of down-counting and up-counting, a time period until the comparison result is reversed if the signal voltage is of a base signal component of each pixel at reset level, and counts, by an other of down-counting and up-counting, the time period if the signal voltage is of a superimposed signal component in which the base signal component is superimposed on a pixel signal component corresponding to an amount of light received by the pixel. The comparison unit has switchable kinds of frequency band characteristics.