Sample and Hold Switch Driver Slope Control for CMOS Image Sensors
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Solution Overview
Problem
In CMOS image sensors, imperfections in sample and hold operations lead to horizontal fixed pattern noise and optical black shifts due to propagation delays, power supply parasitic resistances/capacitances, and mismatches in SHR and SHS control signal drivers, affecting the ideal sampling and holding of image data.
Innovation Solution
Implementing a sample and hold switch driver circuit with slope control to ensure uniform switch-off behavior across all rows of the pixel array, mitigating non-idealities in global sample and hold operations by controlling the slope of switch-off operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sample and hold switch drivers are used without slope control, then the circuit complexity is lower, but horizontal fixed pattern noise and optical black shifts occur due to non-uniform switch-off behavior across rows
Solution Approach 1:
The patent introduces slope control circuits that modify the transition characteristics (slope) of the sample and hold switch drivers. By changing the switching slope parameter, the circuit achieves uniform switch-off behavior across all rows, eliminating horizontal fixed pattern noise and optical black shifts while maintaining reasonable circuit complexity through controlled parameter adjustment rather than fundamental circuit redesign
2Measurement precision
If ideal simultaneous sampling is implemented across all rows, then measurement precision is improved, but propagation delays and power supply parasitic resistances/capacitances cause non-ideal sampling behavior
Solution Approach 1:
The slope control circuits apply preliminary compensation for propagation delays and parasitic effects by pre-adjusting the switching timing and slope characteristics of each row's sample and hold drivers. This preliminary anti-action counteracts the harmful effects of propagation delays and power supply parasitics before they can cause non-ideal sampling, ensuring all rows sample simultaneously and accurately despite the underlying physical imperfections
Data Source
AI summary
A switch driver circuit includes a plurality of pullup transistors. The plurality of pullup transistors includes a first pullup transistor coupled between a voltage supply and a first output node. A plurality of pulldown transistors includes a first pulldown transistor coupled between the first output node and a ground node. A slope control circuit is coupled to the ground node. A plurality of global connection switches includes a first global connection switch coupled between the first output node and the slope control circuit.