Image Sensing Circuit Dynamic Capacitor Charging for High Dynamic Range
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Solution Overview
Problem
Existing image sensing circuits face challenges in achieving a high image brightness dynamic range without increasing circuit cost, as methods like superposition of multiple images or larger capacitors require multiple images or larger circuit areas, respectively.
Innovation Solution
An image sensing circuit and method utilizing a floating node, switch circuit, and counting circuit to dynamically charge and discharge a capacitor, estimating energy through the number of charging and discharging cycles and final potential value, allowing for a high dynamic range in a single image without increasing circuit cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If superposition of multiple images is performed to achieve high image brightness dynamic range, then image brightness dynamic range is improved, but loss of time increases due to requiring multiple images to be shot
Solution Approach 1:
The patent applies preliminary action by performing multiple charging operations on the capacitor during the exposure period before the final readout. The capacitor is charged multiple times with image electric charge from the same exposure, allowing the circuit to accumulate sufficient signal energy without requiring multiple separate image shots. This resolves the contradiction by achieving high dynamic range within a single exposure time rather than through temporal superposition of multiple images.
2Illumination intensity
If sizes of physical capacitors are increased to achieve high image brightness dynamic range, then image brightness dynamic range is improved, but device complexity increases due to larger circuit area occupation
Solution Approach 1:
The patent applies dynamics by introducing a switch circuit that dynamically connects and disconnects the capacitor between the floating node and ground. This dynamic switching enables the capacitor to be repeatedly charged and discharged during the exposure period, allowing a smaller capacitor to accumulate equivalent signal energy that would otherwise require a much larger static capacitor. The dynamic operation resolves the contradiction by achieving high dynamic range with reduced circuit area through temporal multiplexing.
3Device complexity
If dynamic charging and discharging of capacitor is performed to reduce circuit area, then device complexity is reduced, but measurement precision may be affected by switching operations
Solution Approach 1:
The patent applies feedback by using the counting circuit to monitor and record the number of charging and discharging cycles of the capacitor. This feedback mechanism allows the system to track the accumulated signal energy through the count value, which is then used in conjunction with the final capacitor voltage to determine the total image electric charge energy. The feedback resolves the measurement precision concern by providing a digital record of the integration process that compensates for any losses or variations during the dynamic switching operations.
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
Enables precise estimation of image energy and dynamic range in various exposure environments, suitable for both roller blind and global shutters, while maintaining a lower circuit cost by using smaller capacitors, effectively achieving the highest image brightness dynamic range within a single image.
Implementation Method 1
a floating node FD, arranged to receive image electric charge from a photosensitive pixel
Implementation Method 2
at least one capacitor C1, arranged to be dynamically charged and discharged in response to one exposure time period to receive energy of the image electric charge
Data Source
AI summary
An image sensing circuit includes floating node, switch circuit, capacitor(s), and counting circuit. The floating node receives image electric charge from a photosensitive pixel. The switch circuit is coupled between floating node and capacitor(s) to dynamically connect and disconnect floating node and capacitor(s). The capacitor(s) include(s) first terminal(s) connected to switch circuit and second terminal(s) connected to ground. The counting circuit counts the number of charging and discharging behavior of capacitor(s) according to dynamic switches of switch circuit wherein the switch circuit dynamically switches to make capacitor(s) be charged and discharged dynamically in response to one exposure time period to receive energy of image electric charge which is determined by the number of charging and discharging behavior of the capacitor(s) and the capacitor(s)' potential value measured finally.