Light Sensor Signal Conditioning for Ambient Light Cancellation
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Solution Overview
Problem
Proximity light sensors in consumer electronics, such as mobile phones, face challenges in robustly distinguishing between target detection signals and ambient light sources, leading to inaccurate measurements due to varying environmental conditions and sensor assembly variations.
Innovation Solution
A signal conditioning circuit with multiple integration stages and a coupling stage that processes both main detection and ambient light signals to derive an offset signal, improving detection robustness by accounting for various signal sources and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light sensor measures distance by detecting reflected light, then proximity detection function is achieved, but ambient light interference causes measurement inaccuracy
Solution Approach 1:
The measurement process is divided into multiple phases: a first measurement phase where both target light and ambient light are detected, and a second measurement phase where only ambient light is detected. By segmenting the measurement into distinct temporal phases, the circuit can separately capture and later subtract ambient light components from the total signal, eliminating ambient light interference and improving proximity detection accuracy.
Solution Approach 2:
The circuit performs preliminary measurement of ambient light conditions before the actual proximity detection. During the first measurement phase, the ambient light level is captured and stored as a reference value. This preliminary action allows the subsequent proximity measurement to compensate for ambient light by subtracting the pre-captured ambient light reference, thereby maintaining measurement precision under varying ambient light conditions.
2Reliability
If multiple measurement phases are implemented to account for ambient light, then measurement robustness is improved, but circuit complexity increases
Solution Approach 1:
The circuit combines multiple measurement phases and signal processing operations into a single integrated signal conditioning circuit. The first and second integration stages are merged to simultaneously perform integration of sensor signals and generation of offset signals. The coupling stage merges the outputs of both integration stages to produce the final compensated signal. This merging approach achieves robust multi-phase measurement while avoiding the complexity of separate discrete circuits for each function.
Solution Approach 2:
The signal conditioning circuit is designed with multi-functional integration stages that perform multiple operations: the first integration stage integrates both target and ambient light signals during the first measurement phase, while also serving as a reference for ambient light levels. The coupling stage universally handles both signal combination and offset generation functions. This multi-functionality reduces the number of dedicated circuits needed, thereby reducing overall circuit complexity while maintaining measurement robustness.
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 proposed solution enhances the robustness of light sensor measurements by effectively canceling out ambient light and noise, leading to more accurate proximity detection and power-saving functionalities in devices like smartphones.
Implementation Method 1
a photo detector connected to the first sensor input
Data Source
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AI summary
A signal conditioning circuit for a light sensor, in particular for an ambient light sensor, comprises a first integration stage (INT1) connected to a first sensor input (IN1) to receive a first and second sensor signal and a second integration stage (INT2) comprising a coupling input (IN2) to receive from the first integration stage (INT1) a first and second integrated sensor signal. A coupling stage (S3, C5) is connecting the first and second integration stages (INT1, INT2) and is designed to generate a difference signal from consecutively received integrated first and second integrated sensor signals. A sensor arrangement and a method for signal conditioning for a light sensor is also presented.