Sensor Circuit Knee Point Voltage Correction for Dynamic Range
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Solution Overview
Problem
Light sensor pixels reach saturation at different times due to varying light intensities, leading to suboptimal image quality as they stop collecting brightness information once saturated, and existing technologies fail to effectively extend the dynamic range of sensor circuits.
Innovation Solution
Introducing an offset voltage by measuring and correcting the knee point voltage of each pixel sensor, allowing it to be reset to a threshold voltage, thereby extending the dynamic range and preventing saturation during integration time, while minimizing memory and processing impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the photodiode is reset to a fixed threshold voltage (e.g., 0V), then the reset operation is simple, but an offset voltage is introduced that varies between pixels and degrades image quality
Solution Approach 1:
Each pixel measures its own knee point voltage using its dedicated circuitry (collection capacitor, transfer switch, readout switch) without requiring external reference or complex calibration equipment. The pixel self-determines its offset voltage and stores it for correction, enabling each pixel to compensate for its own manufacturing variations independently
Solution Approach 2:
The system measures the actual knee point voltage of each pixel and uses this feedback information to correct the reset voltage. The measured knee point voltage is stored and subsequently used to adjust the reset operation, creating a closed-loop system that compensates for pixel-to-pixel variations and ensures uniform image quality across the sensor array
2Manufacturing precision
If multiple knee point voltage measurements are performed for each pixel, then the offset voltage can be accurately measured and corrected, but the measurement time and processing complexity increase
Solution Approach 1:
The knee point voltage measurements are performed during the manufacturing or calibration phase before the pixel is deployed for normal image capture operations. The measured values are stored in memory associated with each pixel, so that during actual operation no additional measurement time is required - the pre-measured knee point voltages are simply retrieved and used for correction
Solution Approach 2:
Instead of repeatedly measuring the knee point voltage during operation, the system creates a copy of the measurement result (the stored knee point voltage value) that can be referenced multiple times without adding measurement overhead. This copied information is used for voltage correction during normal pixel operation, eliminating the need for repeated time-consuming measurements
3Reliability
If the photodiode is reset multiple times during integration time, then saturation can be prevented, but the circuit complexity and power consumption increase
Solution Approach 1:
The knee point voltage is measured and stored during calibration before normal operation. During actual image capture, the pre-measured knee point voltage is used to set the reset voltage once at the appropriate time, avoiding the need for multiple reset operations during integration. This preliminary measurement approach prevents saturation while maintaining simple circuit operation
Solution Approach 2:
Instead of changing the reset voltage dynamically multiple times during integration, the system changes the parameter of using a measured and stored knee point voltage value that is retrieved from memory. This allows the reset voltage to be adjusted to the correct value without requiring complex real-time control circuitry or multiple reset operations
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 maximizes image quality by ensuring all pixels operate within their dynamic range, preventing saturation and maintaining linearity, with minimal additional circuitry requirements.
Implementation Method 1
light sensor elements, or pixels... the voltage as the y-axis and the time as the x-axis... a pixel with a greater slope reaches saturation level faster
Implementation Method 2
the voltage value of the photodiode may be transferred to the collection capacitor by transferring a charge associated therewith. Measuring the collected charge on the collection capacitor provides the voltage measurement for the pixel
Data Source
AI summary
A method of measuring signals related to a photodiode based sensor and calculating a corrected data value thereof is disclosed. A nominal reset voltage value of the photodiode may be measured. A knee point voltage may be applied to the photodiode and resets a voltage on the photodiode to the knee point voltage when the voltage on the photodiode falls below the knee point voltage. Applying the knee point voltage may extend the dynamic range of the sensor. An output voltage of the photodiode at end of an integration time of the photodiode may be measured. The knee point voltage may be applied again after the end of the integration time. A voltage value of the photodiode of the knee point voltage may be measured. The nominal reset voltage value, the output voltage of a sensor and the knee point voltage may be reported to calculate the corrected data value.