Ambient Light Sensor Using Counter-Based AC Signal Generation
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Solution Overview
Problem
Conventional ambient light detectors are sensitive to flicker from artificial light sources with AC frequencies other than 50 Hz or 60 Hz, particularly those using LED technology, and generate only DC output signals that do not provide information on flicker frequencies, leading to issues like moiré patterns in images.
Innovation Solution
A method and electronic circuit that includes a photodiode, a counter clocked by a first frequency, and a processing stage for digital-to-analog conversion to generate AC signals representing light levels and frequencies, with optional clipping, undersampling, and passband filtering to improve detection accuracy and reduce computational power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional DC output signals are used, then device complexity is reduced, but information on flicker frequencies is lost
Solution Approach 1:
The patent applies periodic action by using a counter clocked at a fixed frequency to generate AC output signals that periodically represent the light level. This periodic counting mechanism inherently encodes frequency information about light source flicker into the output signal, allowing frequency detection without complex additional processing while maintaining manageable device complexity
Solution Approach 2:
The patent changes the output signal parameter from DC to AC, enabling the transmission of frequency information. By converting the output to an AC signal whose characteristics reflect the light source frequency, the system preserves flicker frequency information while keeping the overall device complexity acceptable through straightforward signal generation
2Measurement precision
If photodiode integration period is set to multiple of mains voltage half-period, then flicker detection accuracy is improved, but adaptability to different AC frequencies is worsened
Solution Approach 1:
The patent implements universality by designing a counter-based system that can detect multiple AC frequencies (50 Hz, 60 Hz, and LED frequencies) through a single integrated approach. The counter clocked at a fixed frequency universally handles different light source frequencies without requiring separate detection mechanisms, making the system adaptable to various AC power frequencies and LED driving frequencies
Solution Approach 2:
The patent applies dynamics by allowing the effective integration period to adapt dynamically to different light source frequencies through the counter mechanism. Rather than fixing the integration period to match specific mains frequencies, the system dynamically responds to the actual light source frequency by counting clock cycles, enabling accurate detection across a range of frequencies
3Measurement precision
If high-frequency clock signal is used for counter, then detection precision is improved, but power consumption increases
Solution Approach 1:
The patent applies partial action by using a high-frequency clock to drive the counter only when precise measurement is needed, rather than continuously processing at full resolution. The system can operate with lower effective processing rates when high precision is not required, reducing power consumption while maintaining the capability for high-precision detection when necessary
Solution Approach 2:
The patent changes the operational parameters by allowing the system to adjust between different effective measurement resolutions. By varying the clock frequency or the counting interval, the system can optimize between precision and power consumption based on actual measurement needs, achieving high precision only when required rather than continuously
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
The solution effectively determines light levels and flicker frequencies, allowing for improved image quality by preventing flicker-related issues and reducing power consumption while maintaining design flexibility and precision.
Implementation Method 1
a photodiode illuminated by the ambient luminous radiation
Data Source
AI summary
A method of detecting ambient luminous radiation includes resetting and triggering a counter each time a photodiode illuminated by the ambient luminous radiation reaches a discharge threshold. The counter is then being clocked by a clock signal having a first frequency and delivering a counter output signal. The method further includes generating an AC signal representative of the ambient luminous radiation by converting, from digital to analog, a digital signal obtained from the counter output signal.