Dummy Pixel Noise Correction in Image Sensor VDD Supply
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Solution Overview
Problem
Noise in the VDD supply voltage used to drive imager pixel circuits is transferred to the imager output, degrading image quality, and existing technologies lack effective methods to correct for these voltage level fluctuations.
Innovation Solution
Incorporating two dummy pixels in each row of active pixels, driven by the same VDD supply, to monitor and correct for voltage level shifts between reset and readout, using first and second dummy registers to store signals related to the power supply voltage at these times, allowing for signal correction in active pixel circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dummy pixels are added to monitor power supply voltage, then noise correction capability is improved, but device complexity increases
Solution Approach 1:
The patent creates copies of the power supply voltage condition by using dummy pixels that replicate the same circuit structure as active pixels but without photo-sensitive elements. These dummy pixels serve as voltage sensors, capturing the power supply voltage at different time points (reset and readout) to enable noise correction calculations.
Solution Approach 2:
The patent segments the pixel array into functional zones by inserting dummy pixels at specific locations (every Nth pixel) within each row. This segmentation allows the system to separately monitor power supply voltage conditions without interfering with the primary image sensing function, enabling parallel operation of correction and imaging.
2Reliability
If dummy pixels and registers are added for voltage monitoring, then power supply noise correction is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by making only specific pixels (dummy pixels) have different properties from the active pixels - specifically, removing the photo-sensitive element while keeping the same transistor structure. This localized modification allows voltage monitoring functionality to be added with minimal impact on overall manufacturing processes.
3Measurement precision
If multiple readout operations are performed for voltage measurement, then voltage level determination accuracy is improved, but time consumption increases
Solution Approach 1:
The patent performs preliminary voltage sampling at the reset time point before the actual image readout. By capturing the power supply voltage condition in advance using the dummy pixel during the reset phase, the system eliminates the need for additional time-consuming readout operations during the image acquisition period, thereby improving measurement accuracy without significant time penalty.
Data Source
AI summary
A circuit and method for correcting for power supply voltage noise using two dummy pixels in each row of pixels of an imager having a number of pixels arranged in rows and columns are described. The dummy pixels are driven by the same power supply as the active pixels but do not have the capability to sense light energy. The first dummy pixel is read at the time the active pixels in a row are reset and stores a signal in a first dummy register related to the voltage level of the power supply at the time the active pixels are reset. The second dummy pixel is read at the time the active pixels in the row are read and stores a signal in a second dummy register related to the voltage level of the power supply at the time the active pixels are read. The signals in the first storage register and second storage register can then be used to correct the signals from the active pixels in the row for the effect of noise caused by power supply voltage level fluctuations.