Photodiode Circuit Counter for Ambient Luminosity Detection
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Solution Overview
Problem
Luminosity level detectors face challenges in accurately measuring ambient light due to integration period issues, linearity defects in photodiodes, and sensitivity to flickering artificial light sources, leading to inefficiencies and inaccuracies in measurement.
Innovation Solution
A method and circuit that utilize a counter to track the number of discharge cycles of a photodiode within a set time interval, resetting the photodiode at each discharge threshold, allowing for accurate measurement of light intensity without requiring an analog-to-digital converter, and selecting a discharge time that is a multiple of the AC power supply's half-period to mitigate flickering effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode is used in reverse mode with junction capacitance discharged by photocurrent, then luminosity detection is enabled, but measurement accuracy deteriorates due to integration period issues and linearity defects
Solution Approach 1:
The patent implements dynamic adjustment of the integration period based on the measured luminosity level. The control circuit automatically modifies the integration time to optimize the discharge signal amplitude, ensuring accurate measurements across varying light conditions without manual intervention.
Solution Approach 2:
The system employs feedback mechanisms where the measured luminosity level is used to adjust subsequent measurement parameters. The control circuit receives the measured value and modifies the integration period accordingly, creating a closed-loop system that compensates for linearity defects and maintains measurement accuracy.
2Measurement precision
If the integration period is extended to improve measurement accuracy, then measurement precision improves, but the device becomes more sensitive to flickering artificial light sources
Solution Approach 1:
The patent synchronizes the measurement integration period with the frequency of artificial light sources. By aligning the integration window with the periodic nature of flickering lights (typically 50-120 Hz), the system averages out the fluctuations and eliminates their harmful effect on measurement accuracy.
3Measurement precision
If repeated measurements are performed to adjust integration periods, then measurement accuracy improves, but power consumption and time loss increase
Solution Approach 1:
The system performs preliminary characterization of the photodiode's linearity defects during manufacturing or initial setup. This pre-calibrated data is stored and used to directly compensate for non-linearities in subsequent measurements, eliminating the need for repeated iterative adjustments and reducing both power consumption and measurement time.
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 enables accurate and efficient measurement of luminosity levels across varying conditions, reducing the impact of flickering and linearity defects, and eliminating the need for repeated measurements to adjust integration periods, thereby improving measurement accuracy and reducing costs and power consumption.
Implementation Method 1
Detectors of a luminosity or illumination level are known, which comprise a photodiode used in reverse mode, having its junction capacitance discharged by a photocurrent according to a received light intensity
Data Source
AI summary
The following steps are performed in connection with a photodiode circuit: a) resetting the photodiode circuit; b) determining when a photodiode voltage changes in response to illumination to reach a threshold; and c) updating a counter in response to the determination in step b). The steps a) to c) are repeated until an end of a measurement period is reached. The value of the counter at the end of the measurement period is then output to indicate an intensity of the illumination.