Dynamic Clock Cycle Illuminance Sensor Circuit
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Solution Overview
Problem
Existing display devices have a limited dynamic range for measuring illuminance, making them unsuitable for use in varying light conditions, such as both low-light environments and high-illuminance outdoor settings, which restricts their convenience and functionality.
Innovation Solution
Incorporating a light sensor circuit with a capacitor and light-into-electricity conversion element, an arithmetic circuit, a clock signal generating circuit that gradually changes its cycle, and a sampling latch circuit, allowing for a wide dynamic range of illuminance measurement by extending the clock signal's cycle and using a value conversion circuit with a map table to associate sampled count values with output values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant cycle clock signal is used for illuminance measurement, then the measurement process is simple, but the dynamic range of measurable illuminance is narrow (about 10 times)
Solution Approach 1:
The clock signal generating circuit changes the clock signal cycle dynamically based on the discharge state of the capacitor. When the capacitor discharges quickly (high illuminance), the clock cycle remains short. When the capacitor discharges slowly (low illuminance), the clock cycle extends automatically. This dynamic adaptation allows the system to measure illuminance across a wide range from 1 to 10000 lx without changing hardware complexity.
Solution Approach 2:
The system changes the time parameter (clock signal cycle) adaptively during the measurement process. The clock cycle is extended when the capacitor voltage remains high after a predetermined discharge period, indicating low illuminance conditions. This parameter change enables the counter to capture sufficient count values even in low-light environments, expanding the measurable dynamic range while maintaining simple circuit operation.
2Adaptability or versatility
If the clock signal cycle is extended to measure low illuminance, then the dynamic range increases, but the measurement time increases
Solution Approach 1:
The measurement system uses periodic clock signals to count the discharge events of the capacitor. By adjusting the clock signal period (cycle length) based on the measured illuminance level, the system optimizes the measurement time. For high illuminance, short clock cycles provide rapid measurement. For low illuminance, extended clock cycles allow sufficient counting without excessive time delay, achieving efficient periodic measurement across different lighting conditions.
3Volume of moving object
If a light sensor circuit is integrated in the display panel, then the device size is reduced, but the measurement accuracy may be affected by display pixel interference
Solution Approach 1:
The light sensor circuit is extracted from the main display pixel array and placed in a dedicated region within the display panel. This separation allows the sensor to function independently without interference from pixel operations, while still maintaining integration within the panel structure. The sensor region is designed to receive ambient light separately from the display emission, ensuring accurate illuminance measurement despite the compact integrated design.
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 configuration enables the display device to measure a wide range of illuminance, from low to high levels, enhancing its usability in both indoor and outdoor environments by representing a dynamic range of about 1000 times, thereby improving its convenience and functionality.
Implementation Method 1
a light sensor circuit having a capacitor and a light-into-electricity conversion element that discharges the capacitor according to a surrounding illuminance of the display unit
Data Source
AI summary
A capacitor charged beforehand is discharged according to a light surrounding a display unit. A data is decreased similarly to the voltage between the electrodes of the capacitor. A trigger signal is outputted if the data becomes equal to or less than a threshold value. A clock signal whose cycle of changing levels gradually becomes long is generated. A count value is updated at each change of the clock signal's level and the updated count value is outputted. The count value is sampled when the trigger signal is outputted.