CMOS Image Sensor Transfer Gate Voltage Control
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Solution Overview
Problem
Conventional image sensors fail to adequately address the negative impacts of photodiode dark current and gate-induced drain leakage (GIDL) on floating diffusion dark current, which affect image sensor performance.
Innovation Solution
Implementing a pixel array with transfer gates driven by a transfer gate signal having multiple off state voltage levels, including a higher magnitude first off state voltage level and a lower magnitude second off state voltage level, to reduce dark current during readout operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single off state voltage level is used for the transfer gate, then the device complexity is reduced, but photodiode dark current leakage increases
Solution Approach 1:
The transfer gate off state voltage is changed from a fixed single level to a dynamic multi-level system. The signal generator can selectively apply different off state voltage levels (first off state voltage and second off state voltage) based on operational requirements, making the voltage control adaptive rather than static.
Solution Approach 2:
The patent changes the voltage parameter of the transfer gate control signal from a single fixed value to multiple discrete levels. By varying the voltage level parameter between different off states, the system optimizes the balance between reducing photodiode dark current and managing GIDL effects.
Data Source
AI summary
A CMOS image sensor or other type of image sensor comprises a pixel array and a signal generator coupled to the pixel array. The pixel array comprises a plurality of pixels each having a photosensitive element coupled to a transfer gate. The signal generator is configured to generate a transfer gate signal for application to at least one of the transfer gates. The transfer gate signal has at least an on state voltage level and first and second off state voltage levels, with the first off state voltage level typically having a higher magnitude than that of the second off state voltage level. In an illustrative embodiment, the second off state voltage level is utilized during a readout operation in order to reduce dark current in floating diffusion regions of the pixel array.