Optical Sensor Analog Output Circuit for Ambient Light Saturation
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Solution Overview
Problem
Optical sensor arrangements face saturation issues due to strong ambient light, which overwhelms the signal and affects the accuracy of proximity and gesture detection by overpowering the reflected light signal.
Innovation Solution
An optical sensor arrangement that includes a light sensor connected to a summation node with a current source, an integrator, and a sum and hold circuit, where the current source generates a source current to counteract ambient light, preventing integrator and sum and hold circuit saturation by integrating signals in two phases and forming an analog output signal as a difference between these values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the light sensor detects both reflected light and ambient light, then the sensor can operate in various lighting conditions, but the ambient light causes saturation of the integrator and sum and hold circuit
Solution Approach 1:
The detection process is segmented into two distinct phases: a first integration phase where both reflected light and ambient light are integrated, and a second integration phase where only ambient light is integrated. This segmentation allows the system to separately measure and subsequently subtract the ambient light component from the total signal, preventing saturation while maintaining versatility in various lighting conditions.
Solution Approach 2:
The system performs a preliminary measurement of ambient light during the second integration phase before the reflected light measurement. This preliminary action allows the system to compensate for ambient light effects in advance, enabling accurate detection of reflected light signals even in strong ambient lighting conditions without causing saturation.
2Illumination intensity
If the light sensor detects strong ambient light, then the sensor can function in outdoor conditions, but the ambient light overwhelms the reflected light signal
Solution Approach 1:
The measurement process is divided into two segments: first integrating both reflected light and ambient light, then separately integrating only ambient light in a second phase. By subtracting the second integration result from the first, the system isolates the reflected light signal with high precision, even when ambient light intensity is strong.
Solution Approach 2:
The system uses feedback by measuring the ambient light component separately and using this information to compensate for the total signal. The ambient light measurement from the second integration phase is subtracted from the first integration phase result, providing a feedback mechanism that maintains measurement precision regardless of ambient light intensity.
3Device complexity
If the integrator integrates the sensor current without compensation, then the circuit is simple, but the ambient light causes saturation of the integrator
Solution Approach 1:
The integration process is segmented into two phases with different input conditions: the first phase integrates the sensor current containing both reflected light and ambient light signals, while the second phase integrates only the ambient light component. This segmentation allows the use of a simple integrator circuit without requiring complex saturation prevention mechanisms, as the ambient light component is separately measured and subtracted.
Solution Approach 2:
The system performs a preliminary integration of the ambient light component during the second phase, which allows the main integration of the reflected light signal to be corrected afterward. This preliminary action enables the use of a simple integrator circuit that would otherwise be prone to saturation, by compensating for ambient light effects through the separately measured second integration result.
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 solution effectively reduces the influence of ambient light on the sensor output, preventing saturation and enhancing the accuracy of proximity and gesture detection under various lighting conditions, including strong ambient light.
Implementation Method 1
a light sensor connected to a summation node and designed for generating a sensor current
Implementation Method 2
an integrator coupled to the summation node and designed for generating a first value of an integrator signal by integrating during a first phase and for generating a second value of the integrator signal by integrating during a second phase
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
An optical sensor arrangement (10) comprises a light sensor (11) that is connected to a summation node (13) and is designed for generating a sensor current (S2), a current source (S2) connected to the summation node (13) and designed to provide a source current (S3), and an integrator (21) that is coupled to the summation node (13) and is designed for generating a first value (VP1) of an integrator signal (S6) by integrating during a first phase (P1) and for generating a second value (VP2) of the integrator signal (S6) by integrating during a second phase (P2). The optical sensor arrangement (10) comprises a sum and hold circuit (31) that is coupled to the integrator (21) and is designed to generate an analog output signal (S7) as a function of a difference of the first value (VP1) and the second value (VP2) of the integrator signal (S6).