Image Sensor Row Driver Rise-Time Control for Pixel Reliability
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Solution Overview
Problem
Current image sensors face reliability issues due to short rise times of transmission control signals, which can lead to reduced pixel signal reliability and image quality, especially in pixels adjacent to the row driver.
Innovation Solution
The image sensor incorporates a transmission control signal generator with a current limiter and delay circuit, which adjusts the ON resistance of transistors to prolong the rise time of the transmission control signal, ensuring a more reliable signal transmission to the pixel array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transmission control signal is generated with fast switching transistors, then the switching speed is improved, but the rise time becomes too short causing charge loss and reduced pixel signal reliability
Solution Approach 1:
The patent changes the electrical parameters of the transmission control signal by introducing a delay circuit that prolongs the rise time from potentially sub-nanosecond ranges to a controlled 1-500 ns range. This parameter modification ensures that charges have sufficient time to stabilize in the floating diffusion node before readout, preventing charge loss while maintaining efficient signal transmission.
Solution Approach 2:
The patent introduces a delay circuit as an intermediary component between the control signal generator and the transmission transistor gate. This intermediary element mediates the conflict between fast switching and reliable signal transmission by temporarily holding the control signal, allowing charges to settle before the transmission gate fully opens, thus ensuring pixel signal reliability without sacrificing overall system speed.
2Reliability
If the rise time of the transmission control signal is prolonged, then the pixel signal reliability is improved, but the transmission speed is reduced
Solution Approach 1:
The patent applies partial action by implementing a delay circuit that provides just enough delay (1-500 ns) to ensure reliable pixel signal transmission without excessive prolongation that would unnecessarily slow down the overall system. The delay is calibrated to be sufficient for charge stabilization but minimal enough to maintain high transmission productivity.
3Area of stationary object
If pixels adjacent to the row driver are used, then the device area is reduced, but the signal reliability is compromised due to short rise times
Solution Approach 1:
The patent applies local quality by implementing a uniform delay circuit architecture across all pixel rows, ensuring that pixels adjacent to the row driver receive the same rise time prolongation treatment as distant pixels. This localized correction at each row driver output ensures consistent signal reliability throughout the image sensor array, enabling compact design without sacrificing quality.
Data Source
AI summary
An image sensor including: a pixel array including pixels each pixel including a photoelectric conversion element, a transmission transistor to transmit photocharges generated by the photoelectric conversion element to a floating diffusion node, and a reset transistor to reset the floating diffusion node based on a pixel power voltage; and a row driver to control the pixels, wherein the row driver includes a transmission control signal generator to provide a transmission control signal to the transmission transistor, wherein the transmission control signal generator includes: a first transistor to which a first voltage is applied; a second transistor connected to the first transistor; a third transistor to which a second voltage is applied, the second voltage being higher than the first voltage; and a fourth transistor connected to the third transistor, wherein an ON resistance of the second transistor is different from an ON resistance of the first transistor.