Image Sensor Reset Current Compensation for High Luminance Blackening
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Solution Overview
Problem
Conventional image sensors experience a phenomenon where high luminance areas, such as sunlight, appear black due to a sudden drop in reset voltage during reading, leading to a small voltage difference between signal and reset voltages, and existing solutions increase chip size and introduce dispersion in color representation.
Innovation Solution
An image sensor with a reset current supply section that maintains a constant sum of first and second reset currents, using a reset current supply circuit with a longer gate length transistor to compensate for the first reset current's drop, thereby preventing the reset voltage from dropping and reducing color dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional correlated double sampling circuit is used to read reset voltage and signal voltage, then reset noise can be removed, but high luminance areas appear black due to sudden drop in reset voltage
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation current that flows in the opposite direction to the problematic first reset current. This compensation current counteracts the sudden voltage drop caused by the first reset current, preventing the blackening of high luminance areas before it occurs during the reset voltage reading period.
Solution Approach 2:
The patent uses an intermediary approach by introducing a compensation current as a mediating element between the first reset current and the read line. This compensation current acts as a buffer that maintains the reset voltage level, allowing the correlated double sampling circuit to function properly without the blackening artifact.
2Reliability
If existing solutions are implemented to prevent reset voltage drop, then chip size increases and color dispersion is introduced
Solution Approach 1:
The patent applies self-service by designing a circuit where the compensation current is generated automatically based on the actual first reset current flowing through the pixel. The compensation current supply circuit responds to the conditions in real-time without requiring external control signals or complex detection circuits, thereby maintaining simplicity while ensuring reset voltage stability.
3Reliability
If a compensation current is supplied to maintain constant sum of reset currents, then reset voltage drop is prevented, but circuit complexity increases
Solution Approach 1:
The compensation current supply circuit operates autonomously by detecting the conditions of the first reset current and automatically providing the appropriate compensation current. This self-service mechanism eliminates the need for complex external control circuits while maintaining reset voltage stability.
Solution Approach 2:
The patent changes the parameter of compensation current based on the operating conditions. The compensation current is dynamically adjusted to match the first reset current characteristics, allowing the circuit to adapt to different luminance conditions without requiring complex control logic.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution prevents the blackening of high luminance subjects and reduces color dispersion without increasing chip size, ensuring accurate representation of high luminance areas without the need for complex detection circuits.
Implementation Method 1
a photo diode PD which is a photoelectric conversion element for converting light into electrons
Data Source
AI summary
An image sensor is disclosed. The image sensor includes a plurality of pixels arranged in a matrix which detects a pixel signal of each pixel based on a voltage difference between a reset voltage which is a reference voltage of each pixel and a signal voltage generated by a photoelectric conversion at each pixel, and includes a plurality of read lines located for each pixel column, wherein the reset voltage and the signal voltage are read from the pixel of the corresponding pixel column; and a reset current supply section provided for each read line, wherein at the same time a first reset current is supplied from a pixel to the read line when reading the reset voltage from the pixel, the section supplies a second reset current to the read line such that a sum of the first reset current and the second reset current is constant.