CMOS Image Sensor Photodiode Mode Switching for Dynamic Range
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Solution Overview
Problem
Conventional CMOS image sensors have a limited dynamic range due to the initial charge amount accumulated in the photodiode's reset state, which restricts their ability to detect both high-intensity and low-intensity light effectively without increasing the power supply voltage, thereby negating the advantage of low power consumption.
Innovation Solution
The photodetection apparatus switches between voltage and current output modes based on light intensity, using a control unit to activate either the voltage output unit or the current output unit, and includes a current/voltage conversion unit to expand the dynamic range without increasing the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the initial charge amount in the photodiode is increased to expand the dynamic range, then the detection capability for high-intensity light is improved, but the power supply voltage must be increased, which increases power consumption
Solution Approach 1:
The pixel circuit is divided into two operational modes: voltage output mode for low-intensity light detection and current output mode for high-intensity light detection. This segmentation allows the system to optimize performance for different light conditions without requiring a single high-voltage design, thereby maintaining low power consumption while expanding the overall dynamic range.
Solution Approach 2:
The pixel circuit dynamically switches between voltage output mode and current output mode based on the intensity of incident light. This dynamic operation allows the circuit to adapt its detection mechanism in real-time, enabling wide dynamic range coverage without the need for continuously high power supply voltage, thus avoiding increased power consumption.
2Measurement precision
If the power supply voltage is increased to increase the initial charge amount, then the dynamic range is expanded, but the advantage of low power consumption in CMOS sensors is lost
Solution Approach 1:
The circuit changes its operational parameters by switching between voltage mode and current mode based on light intensity. In voltage mode, it operates with low power supply voltage for sensitivity; in current mode, it directly outputs photoelectric current for high-intensity light. This parameter change allows wide dynamic range without requiring continuously high voltage, preserving low power consumption characteristics.
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 approach allows for increased dynamic range detection of light intensities without raising the power supply voltage, maintaining low power consumption and enhancing sensitivity to both weak and high-intensity light, thereby improving the overall performance of the CMOS image sensor.
Implementation Method 1
the photodiode PD receives light, photoelectric current flows
Data Source
AI summary
A set of voltage output units outputs the light intensity detected by a photodetection device in the form of a voltage value. With the set of voltage output units, the capacitance of the cathode terminal of a photodiode PD provided within the pixel is charged or discharged using the photoelectric current. A current output unit outputs photoelectric current Iph flowing from the photodetection device. The current output unit includes a current output transistor provided between one terminal of the photodetection device and the data line. A pixel circuit effects control of the pixel so as to activate either the set of the voltage output units or the current output unit, thereby outputting either voltage value or photoelectric current to the data line connected to the pixel.