Active Pixel Sensor Dark Current Reduction via Feedback Control
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Solution Overview
Problem
CMOS imaging sensors face significant challenges due to high dark leakage current from photodiodes, which can render sensors ineffective for infrared light sensing, especially when using less expensive materials like germanium, as the leakage current can be of the same order as the current induced by photons, making it indistinguishable.
Innovation Solution
An active pixel sensor design that incorporates a photodiode and an integrator circuit with a feedback loop to set a reverse bias voltage, reducing dark leakage current to a desired level, allowing for effective light intensity measurement by isolating and compensating for dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If less expensive semiconductor materials like germanium are used for photodiodes, then manufacturing cost and availability improve, but dark leakage current increases making the sensor useless for infrared light sensing
Solution Approach 1:
The patent implements a feedback control system where the measured pixel voltage (representing integrated dark current) is fed back to adjust the reverse bias voltage on the photodiode. The integrator circuit continuously monitors the dark current level and automatically adjusts the bias voltage to maintain it at an optimal level, creating a closed-loop control system that dynamically compensates for material-related dark current variations
Solution Approach 2:
The patent changes the reverse bias voltage parameter dynamically to control and reduce dark leakage current. By adjusting this electrical parameter through the feedback loop, the system optimizes the operating point of the photodiode to minimize dark current while maintaining sensitivity to incident light, enabling the use of germanium and other cost-effective materials
2Ease of operation
If photodiodes operate at room temperature, then ease of operation improves, but dark current increases to the same order of magnitude as photon-induced current
Solution Approach 1:
The patent extracts and separates the dark current component from the total current signal by using the integrator circuit to measure and integrate only the dark current portion (when no light is incident). This extracted dark current measurement is then used by the feedback loop to compensate for its effect, effectively removing the harmful dark current component from the measurement while maintaining room temperature operation
Solution Approach 2:
The integrator circuit acts as an intermediary that measures and quantifies the dark current level, serving as a bridge between the photodiode output and the feedback control mechanism. This intermediary component enables the system to indirectly control and compensate for dark current effects without requiring direct manipulation of the photodiode operation
3Object-generated harmful factors
If reverse bias voltage is increased to reduce dark leakage current, then dark current decreases, but sensitivity to incident light may be affected
Solution Approach 1:
The patent employs dynamic adjustment of the reverse bias voltage through the feedback control loop rather than using a fixed bias voltage. The system continuously adapts the bias voltage level based on real-time measurements of dark current, allowing it to optimize the trade-off between dark current suppression and light sensitivity. This dynamic approach enables the system to maintain optimal performance across varying operating conditions
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 enables the use of less expensive semiconductor materials like germanium for image sensing arrays by reducing dark leakage current, enhancing the sensor's ability to accurately detect light intensity and effectively sense infrared light, while maintaining sensitivity and reducing noise.
Implementation Method 1
Each light-sensitive element in a pixel generates a separate electrical current, which is proportional to the intensity of the incident light on that element
Implementation Method 2
a feedback loop configured to receive the pixel voltage and control the integrator circuit to adjust the reverse bias voltage to substantially reduce the dark leakage current through the photodiode to a desired level
Data Source
AI summary
An active pixel sensor comprises a photodiode providing a photodiode output current indicative of an intensity of light incident the photodiode and an integrator circuit electrically coupled to the photodiode. The integrator circuit is configured to provide a pixel voltage representing an integration of the photodiode output current when the photodiode is exposed to light and dark leakage current through the photodiode when the photodiode is not exposed to light. The integrator circuit is configured to set a reverse bias voltage on the photodiode and respond to at least one control input to set the reverse bias voltage to a first level. The active pixel sensor comprises a feedback loop configured to receive the pixel voltage and control the integrator circuit to adjust the reverse bias voltage to substantially reduce the dark leakage current through the photodiode to a desired level.