Variable Low Pass Filter for Radiation Imaging Readout
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Solution Overview
Problem
Existing radiation imaging apparatuses, such as those described in Japanese Patents No. 4619640 and No. 4448042, are unable to sufficiently shorten the readout time of pixel signals due to the temporary decrease in the time constant of the low pass filter only during amplifier resetting.
Innovation Solution
The proposed imaging apparatus includes a variable low pass filter with a control circuit that adjusts its time constant after the first sample-and-hold circuit finishes sampling and increases it during the second sample-and-hold circuit's sampling, allowing for a more efficient readout of pixel signals by optimizing noise removal and response stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the time constant of the low pass filter is temporarily decreased only during amplifier resetting, then the response stabilization is achieved, but the overall pixel signal readout time cannot be sufficiently shortened
Solution Approach 1:
The low pass filter's time constant is made dynamically variable rather than fixed. The control circuit adjusts the time constant based on the operational phase: decreasing it during amplifier resetting for rapid response stabilization, and increasing it during pixel signal readout for efficient noise filtering, thereby resolving the contradiction between response speed and noise removal efficiency
Solution Approach 2:
The time constant of the low pass filter is periodically adjusted according to the imaging operation phases. The control circuit implements periodic switching between different time constant values - a shorter time constant during reset operations and a longer time constant during signal readout - optimizing performance for each phase while minimizing overall readout time
2Reliability
If the time constant of the low pass filter is increased to remove high-frequency noise, then noise removal efficiency is improved, but the response time of the integral amplifier output increases
Solution Approach 1:
The time constant parameter of the low pass filter is changed according to operational requirements. By switching between different time constant values - longer during signal readout for noise removal and shorter during reset for fast response - the system achieves both noise removal efficiency and rapid response without compromise
Data Source
AI summary
An imaging apparatus includes a pixel that generates charge; an integral amplifier that integrates charge transferred from the pixel; a low pass filter to which output of the integral amplifier is supplied and whose time constant is variable; first and second sample-and-hold circuits that sample and hold output of the low pass filter before and after the charge is transferred from the pixel to the integral amplifier, respectively; a differential circuit that outputs a difference between signals held by the first and second sample-and-hold circuits; and a control circuit that changes the time constant. The control circuit decreases the time constant after the sampling by the first sample-and-hold circuit ends, and increases the time constant in the middle of the sampling by the second sample-and-hold circuit.