Image Sensor Ambient Light Measurement Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ambient luminosity measurement circuits face challenges in maintaining consistent light response across different operating modes of image sensors, leading to increased power consumption and complexity, particularly due to differences in dark current effects during image acquisition and non-image phases.
Innovation Solution
The solution involves using an image sensor's photodiodes to measure ambient luminosity by selecting a subassembly of pixels in a second operating mode, applying control signals similar to image acquisition phases, and maintaining transfer transistors in the off state, while adjusting integration time and using only green pixel values for accurate measurements, and incorporating standby periods to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode is used to measure ambient luminosity, then the measurement function is achieved, but the cost, complexity, and bulk of the device increase
Solution Approach 1:
The image sensor is designed to perform multiple functions: capturing images in the first operating mode and measuring ambient luminosity in the second operating mode. By reusing the same sensor hardware for both purposes, the patent eliminates the need for a separate dedicated photodiode, thereby reducing device complexity, cost, and bulk while maintaining measurement capability
Solution Approach 2:
The patent combines the image sensor and ambient luminosity measurement functionality into a single integrated system. The control circuit manages both image capture and luminosity measurement operations using the same sensor array, merging what would traditionally be separate components into one unified device
2Measurement precision
If the sensor operates in image acquisition mode, then images are provided, but power consumption increases and dark current effects vary
Solution Approach 1:
The control circuit dynamically switches between two operating modes based on the required function: image acquisition mode when images are needed, and luminosity measurement mode when only ambient light level is required. This dynamic operation allows the system to optimize power consumption by activating only the necessary functionality at any given time
Solution Approach 2:
In the luminosity measurement mode, the control circuit periodically performs measurements rather than continuously operating in image acquisition mode. This periodic action reduces average power consumption while still providing accurate luminosity data when needed
3Measurement precision
If all pixels are used for luminosity measurement, then measurement coverage is maximized, but power consumption and processing complexity increase
Solution Approach 1:
The sensor array is segmented into multiple pixels, and the control circuit is designed to selectively activate and read out specific pixels based on the operating mode. In luminosity measurement mode, the control circuit can read out pixel values independently without requiring complex processing of all pixels, simplifying the control architecture while maintaining measurement accuracy
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 approach ensures coherent luminosity measurements across modes, reduces power consumption, and maintains consistent dark current effects, achieving accurate ambient luminosity values with minimal power usage comparable to dedicated photodiodes.
Implementation Method 1
a photodiode used in reverse mode, having its junction capacitance discharged by a photocurrent according to a received light intensity
Data Source
AI summary
A device includes an image sensor and a circuit for controlling the sensor. The control circuit is configured control the device in a first operating mode and second operating mode. In the first operating mode images acquired by the sensor are output. In the second operating mode, no images are provided, but a selected subassembly of pixels of the image sensor are read and image data therefrom is processed to provide an ambient luminosity value.