Guard Region CMOS Imaging Array Exposure Detection
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Solution Overview
Problem
Conventional CMOS image sensors in dental x-ray systems face challenges in synchronizing exposure with x-ray pulses without increasing patient dose and system cost, due to limitations in existing synchronization methods that either waste x-ray exposure time or consume high power.
Innovation Solution
Incorporating a guard region around the CMOS imaging array that acts as a large-area exposure detector, using a current detector to generate trigger signals based on the current flowing through the guard region, allowing for precise detection of exposure start and end without additional sensors or high power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate detectors are used to detect the beginning of x-ray exposure, then the imaging sensor can be triggered to start exposure, but the detection time is a significant fraction of the image exposure time, wasting x-ray exposure and increasing patient dose
Solution Approach 1:
The guard region is merged with the imaging array structure, forming an integrated device where the guard region acts as both a protective structure and a light-sensitive detection region. This eliminates separate detectors and their associated timing delays, allowing simultaneous image capture and exposure detection without additional time overhead.
Solution Approach 2:
The guard region serves multiple functions: it protects the imaging array from electrical interference while simultaneously acting as a light-sensitive detector for exposure timing. This multi-functionality eliminates the need for dedicated separate detectors, reducing system complexity and timing overhead.
2Measurement precision
If the imaging array is continually cycled with repeated readout to detect exposure start, then a representative set of photodiodes can be monitored, but power consumption increases significantly
Solution Approach 1:
The detection function is extracted from the main imaging array and assigned to the dedicated guard region. This allows the imaging array to remain in a low-power state during detection phases, with only the guard region actively monitoring for exposure conditions, thereby significantly reducing overall power consumption.
Solution Approach 2:
The guard region autonomously detects exposure conditions and generates trigger signals without requiring continuous readout of the entire imaging array. This self-service capability eliminates the need for power-intensive repeated readout cycles while maintaining accurate exposure detection.
3Measurement precision
If separate sensors are provided with each imaging array to detect exposure, then exposure detection can be performed, but the cost of the imaging system increases
Solution Approach 1:
The detection capability is merged into the guard region that is already part of the imaging array structure. This integration eliminates the need for separate additional sensors, reducing component count, system complexity, and overall cost while maintaining exposure detection functionality.
Solution Approach 2:
The guard region is designed to serve dual purposes: protecting the imaging array from electrical interference and detecting light for exposure timing. This multi-functionality eliminates the need for dedicated separate sensors, reducing system cost and complexity.
4Object-affected harmful factors
If the imaging array is reset close to the beginning of x-ray pulse, then dark current background is minimized, but synchronization with x-ray pulse is required
Solution Approach 1:
The guard region autonomously detects the start of the x-ray pulse and automatically triggers the reset operation without requiring external synchronization signals. This self-service capability eliminates complex synchronization systems while achieving minimal dark current background through timely reset.
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 reduces dark current accumulation, minimizes unnecessary x-ray exposure, and lowers system costs by using the guard region to detect exposure events efficiently, thereby improving image quality and reducing patient dose.
Implementation Method 1
The guard region is exposed to light when the array of pixel sensors is exposed to light
Implementation Method 2
a CMOS imaging array that is covered with a layer of scintillation material that converts the x-rays to visible light that can be detected by the image sensor
Data Source
AI summary
A camera having an exposure detector is disclosed. The camera includes an array of pixel sensors, CMOS circuitry that is separate from the array of pixel sensors, a guard region, and a current detector. The guard region separates the CMOS circuitry from the array of pixel sensors. The guard region is positioned such that the guard region is exposed to light when the array of pixel sensors is exposed to light. The current detector measures the current flowing from the guard region to a power rail when the guard region is biased to a predetermined potential and generates a start trigger signal when the current exceeds a threshold value. A controller resets the pixel sensors in response to the start trigger signal.