Active Pixel Array Column-Read Transistor Reset Voltage Control
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Solution Overview
Problem
The existing image sensor arrays face issues with reset reference voltage differences between columns and rows, leading to inconsistencies in initial exposure values due to varying impedance and current drops across the power source and source followers, causing inaccuracies in signal reading and exposure.
Innovation Solution
The method involves controlling the sequence of transistors and switches to maintain identical reset reference voltages during exposure and signal reading by turning on the transfer and reset transistors, keeping the column-read transistor off during reset, and ensuring all source followers on a row are off during exposure and signal reading, thus stabilizing the reset reference voltage across all active pixel elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If power is provided to each row separately through power cables, then each row can be independently powered, but impedance differences in power cables cause voltage drops that create reset reference voltage differences between columns and rows
Solution Approach 1:
The patent applies equipotentiality by ensuring all source followers operate at the same reference voltage level. By controlling the timing of transistor operations and maintaining identical drain voltages for reset transistors across all pixels during reset and signal reading phases, the invention eliminates voltage drops caused by power cable impedance, achieving uniform reset reference voltage across the entire sensor array.
2Productivity
If source followers remain on during reset operation to enable signal reading, then reading capability is maintained, but current flow through power cables creates voltage drops that cause reset reference voltage differences
Solution Approach 1:
The patent applies periodic action by implementing strict timing control of transistor operations. The method uses periodic on/off cycles of the reset transistor and column-read transistor, ensuring that during both reset operation and signal reading phases, the drain voltage of the reset transistor remains identical. This timing-based control eliminates voltage drops while maintaining reading capability.
3Adaptability or versatility
If different power cables are used for each row, then each row can be independently controlled, but impedance variations in different power cables cause different current drops and reset reference voltage differences
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the operational state of transistors to compensate for power cable impedance differences. By changing the timing parameters of transistor switching and maintaining identical drain voltages regardless of which power cable is used, the invention eliminates the effect of impedance variations, ensuring consistent reset reference voltage and initial exposure values across all rows.
Data Source
AI summary
An active pixel element of an image sensor array includes a sensor, a transfer transistor, a reset transistor, and a source follower. There is a column-read transistor positioned in each column of the image sensor array for controlling the read signals. When the sensor is reset, all column-read transistors are turned off while the transfer transistor and the reset transistor are turned on. When a reset signal is read and all column-read transistors are still turned off, the reset transistor is turned on so as to generate the same reset reference voltage when the sensor is reset. In this way, there is no difference in reset reference voltage between each column and between each row for the image sensor array.