Radiation Detector APS Pixel Bias Current Compensation
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Solution Overview
Problem
Radiation detectors based on the Active Pixel Sensor (APS) method face issues with noise in the final image due to variations in the initial state among pixels, requiring pixel initialization, and the readout circuit can only operate within a limited range due to bias current saturation.
Innovation Solution
Incorporating a current adjustment part connected to the signal output line to draw or feed a current equivalent to the bias current flowing to the current signal generation part when no charge is stored, allowing for a wider detectable range for the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current signal generation part is used to generate a current signal corresponding to the charge stored in the pixel, then the detectable range for the output signal is improved, but the readout circuit is influenced by bias current which limits the operating range
Solution Approach 1:
A current adjustment part is introduced as an intermediary component connected between the pixel and the signal readout circuit. This current adjustment part compensates for the bias current by drawing or feeding a current approximately equivalent to the bias current, thereby eliminating the influence of bias current on the readout circuit and expanding the detectable range without adding significant complexity
Solution Approach 2:
The current adjustment part dynamically adjusts the current parameter in the signal output line to compensate for bias current variations. By changing the current parameter to match the bias current, the system eliminates the limiting effect of bias current on the readout circuit while maintaining the improved detectable range provided by the current signal generation part
2Reliability
If the readout circuit operates with bias current flowing to the current signal generation part, then the circuit can function, but the operating range is limited due to bias current saturation
Solution Approach 1:
The current adjustment part serves as a mediator that handles the bias current compensation, allowing the readout circuit to operate reliably while preventing bias current saturation from limiting the operating range. The current adjustment part absorbs the bias current effect, enabling the system to maintain reliable operation across a broader operating range
3Measurement precision
If pixel initialization is performed to reduce noise due to variations in initial state among pixels, then the noise in the final image is reduced, but the complexity and time for readout operations increases
Solution Approach 1:
The current adjustment part automatically compensates for pixel-to-pixel variations in bias current without requiring external initialization operations. Each pixel's current adjustment part self-regulates the bias current effect, reducing noise inherent to the APS method while avoiding the complexity and time overhead of manual pixel initialization procedures
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 configuration eliminates the influence of bias current on the readout circuit, enabling a broader dynamic range for the current signal corresponding to the charge stored in the pixel, thus improving the detectable range and reducing noise.
Implementation Method 1
The photodiode 101 photoelectrically converts light (radiation) in a predetermined frequency band which is incident from the outside and stores charge generated through the photoelectric conversion in the charge storage part 102
Data Source
AI summary
A detectable range for an output signal corresponding to charge stored at a pixel is widened in a radiation detector based on an APS method. A resistor (42) is connected to a region between a pixel (12) and a signal readout circuit (21) in a signal output line (51). The resistor (42) is set so as to draw, from the signal output line (51), a current approximately equivalent to a bias current which flows to an amplifier transistor (16) when no charge is stored in a charge storage part (14).