CMOS TDI Sensor for X-ray Imaging
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Solution Overview
Problem
Current CCD TDI sensors are unsuitable for industrial X-ray inspection due to large pixel size limitations, which slow down scanning speed, and are susceptible to X-ray radiation damage, reducing their usable lifetime.
Innovation Solution
Implementing a Time Delay and Integration (TDI) image sensing system using CMOS circuitry with charge integrating and summing amplifiers, allowing for larger pixel sizes and separation of CMOS circuitry from photodiode detectors to shield from radiation, enabling high-speed scanning and extended lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If CCD TDI sensor is used with large pixel size for industrial X-ray inspection, then detection area is improved, but scanning speed decreases significantly
Solution Approach 1:
The sensor array is divided into multiple independent pixel elements that can be scanned in parallel. Each pixel element processes X-ray signals independently, allowing the system to maintain high scanning speed while using large pixel sizes suitable for industrial inspection applications.
Solution Approach 2:
The patent replaces the mechanical charge transfer mechanism of CCD with electronic readout circuitry. This substitution eliminates the speed limitation imposed by physical charge transfer across large pixel arrays, enabling fast electronic scanning while maintaining large pixel dimensions for industrial X-ray inspection.
2Reliability
If CCD TDI sensor is exposed to high X-ray radiation in industrial inspection, then detection capability is maintained, but sensor lifetime is reduced due to radiation damage
Solution Approach 1:
The patent employs a sensor design where the photodetector array can be replaced more easily and cost-effectively than the entire imaging system. This allows the detector array to be treated as a replaceable component that can withstand high radiation environments for extended periods before replacement, effectively managing radiation-induced degradation.
Solution Approach 2:
The patent implements radiation hardening techniques and protective measures before the sensor is deployed in high-radiation environments. This includes selecting radiation-tolerant materials, designing shielding structures, and implementing error correction algorithms that compensate for radiation-induced defects, thereby extending the operational lifetime of the sensor in industrial X-ray inspection applications.
3Productivity
If scan speed is increased in normal line scan application, then productivity is improved, but integrated light signal decreases
Solution Approach 1:
The patent combines multiple pixel signals through electronic summation and integration circuits. By merging the output signals from multiple large pixels and integrating them over time, the system maintains high signal levels even at increased scan speeds, resolving the trade-off between productivity and signal quantity in industrial X-ray inspection.
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
The CMOS TDI sensor achieves high-speed scanning with larger pixel sizes and improved resistance to X-ray radiation damage, making it suitable for industrial X-ray inspection applications while reducing manufacturing costs.
Implementation Method 1
Each TDI stage contains a photodiode detector, a plural of amplifiers, a plural of storage capacitors, and a plural of control switches
Implementation Method 2
The first stage of CCD integrates the light signal within one integration time which equals to one line time
Implementation Method 3
The signal charge will then transfer from the first stage to the second stage of CCD while the object under scan also moves from the first stage to the second stage of CCD in synchronization with the movement of the signal charge
Data Source
AI summary
A CMOS TDI image sensor consists of M pixels where each pixel is formed by a column of N TDI stages. Each TDI stage contains a photodiode that collects photo-charge and a pre-amplifier that proportionally converts the photo-charge to a voltage. Each TDI stage also has a set of capacitors, amplifiers, and switches for storage of the integrated signal voltages, where Correlated Double Sampling (CDS) technique (true or pseudo) maintains both photo-signal and reset voltages simultaneously. The CDS signal voltages can be passed from one TDI stage to the next TDI stage along a column for summing. The CDS signal voltages of the last TDI stages of M pixels are read out with a differential amplifier. This CMOS TDI structure is especially advantageous for implementing X-ray scanning detector systems requiring large pixel sizes and signal processing circuitry that is physically separated from the photodiode array for X-ray shielding.