Proximity Sensor Switching Circuit for Sunlight Interference
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Solution Overview
Problem
Mobile phones and digital cameras equipped with proximity and range-finding sensors often malfunction due to irradiation from outside ambient light sources like sunlight, leading to inaccurate detection of objects.
Innovation Solution
A sensor device configuration that includes a light emitting element, an analog-to-digital conversion section, a photodiode, a comparison section, a change-over switch, an open-close switch, and a variable current source, which allows for accurate determination of object proximity by isolating the influence of external light through controlled current subtraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional proximity sensor uses a photodiode to detect reflected light from a light emitting element, then it can determine object proximity, but it malfunctions when irradiated by outside ambient light sources like sunlight causing inaccurate detection
Solution Approach 1:
The detection process is segmented into two distinct phases: a measurement phase where the light emitting element is activated to detect reflected light, and a reference phase where the light emitting element is deactivated to measure only ambient light. This segmentation allows the system to separately quantify and subsequently subtract the harmful ambient light component from the total light signal, thereby eliminating its interfering effect on proximity detection accuracy
Solution Approach 2:
The system performs a preliminary measurement of the ambient light level by activating the reference signal generator before the actual proximity measurement. This preliminary action captures the baseline ambient light condition, which is then stored and used as a reference value to be subtracted from the subsequent measurement signal, effectively pre-compensating for the harmful ambient light influence
2Area of stationary object
If a single device is configured to detect both illuminance and proximity, then it can reduce device size, but it becomes more complex to accurately distinguish between ambient light and reflected light signals
Solution Approach 1:
The system dynamically switches between two operational modes using a switch controlled by a control signal: a measurement mode where the light emitting element is on and both reflected light and ambient light are detected, and a reference mode where the light emitting element is off and only ambient light is detected. This dynamic switching capability allows a single photodiode to perform both illuminance and proximity detection functions while enabling the system to mathematically separate the two light components through subtraction of the reference signal from the measurement signal
Solution Approach 2:
The photodiode is designed to serve multiple functions: it acts as both an illuminance sensor (detecting ambient light when the light emitting element is off) and a proximity sensor (detecting reflected light when the light emitting element is on). By universally utilizing the same light-receiving element for both detection purposes and employing signal subtraction to distinguish between the two functions, the device achieves multi-functionality without requiring separate sensors, thereby reducing overall device size
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 enables accurate detection of object proximity without malfunctions caused by external light sources, ensuring reliable operation even under high illuminance conditions.
Implementation Method 1
a light receiving element which is a photodiode PD
Data Source
AI summary
The present invention provides a sensor device and an electronic apparatus each of which does not make malfunction derived from outside ambient light such as sunlight. In the sensor device, an ADC outputs, to one of two input terminals of a comparison circuit, second data which is a digital value ADCOUT corresponding to a current Iin−I1 being the result of subtraction from a current I1 from a current Iin and which is larger than a threshold Data_th.