Ambient Light Nullification in Optical Measurement Systems
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Solution Overview
Problem
Traditional optical measurement systems face challenges in accurately measuring ambient light, particularly in time-of-flight distance measurement systems, due to the complexities in determining an optimal sampling period, leading to either measurement delays or improper light level measurements.
Innovation Solution
An optical measurement system that incorporates a photodetector coupled with a field effect transistor (FET) in a sample and hold circuit, allowing for selective time constants to be applied using a time constant selector circuit with capacitors, enabling accurate detection of ambient light and subsequent measurement of desired light signals by nullifying ambient light effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an excessively long sampling period is used to detect ambient light, then measurement accuracy is improved, but measurement delay increases and the ambient light may change during the measurement process
Solution Approach 1:
The system performs preliminary action by measuring ambient light levels before the actual distance measurement process. The ambient light sensor captures ambient light intensity in advance, allowing the system to compensate for ambient light effects during subsequent reflected light detection without requiring a lengthy sampling period during the actual measurement phase.
Solution Approach 2:
The measurement process is segmented into separate phases: an ambient light measurement phase using a dedicated ambient light sensor, and a reflected light detection phase for distance measurement. This segmentation allows each phase to be optimized independently, with the ambient light measurement occurring beforehand and the distance measurement proceeding without time delay.
2Productivity
If a short sampling period is used for ambient light detection, then measurement speed is improved, but measurement accuracy deteriorates
Solution Approach 1:
An intermediary ambient light sensor is introduced into the system, separate from the main reflected light detector. This intermediary sensor专门 measures ambient light levels and provides compensation data to the main detector, allowing the main detector to operate at high speed without sacrificing accuracy, as the ambient light effects are compensated using data from the specialized sensor.
3Device complexity
If traditional ambient light measurement circuitry is used in time-of-flight systems, then device complexity is reduced, but measurement precision deteriorates due to inadequate ambient light compensation
Solution Approach 1:
A dedicated ambient light sensor serves as an intermediary component that separately measures ambient light intensity. This sensor feeds compensation signals to the main distance measurement circuitry, enabling precise ambient light compensation without requiring the main circuit to handle both ambient and reflected light measurement functions simultaneously, thus maintaining reasonable device complexity while improving measurement precision.
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 allows for precise detection of current flow through the photodetector, effectively eliminating the adverse effects of ambient light, thereby enhancing measurement accuracy and speed in various applications, including time-of-flight distance measurement systems.
Implementation Method 1
Optical measurement systems typically employ one or more photodetectors to detect incident light and then use information derived from the detected light for various purposes
Implementation Method 2
The FET is a part of a sample and hold circuit and an amount of current that flows through the photodetector is proportional to a conductivity state of the FET. The conductivity state of the FET is determined by a voltage bias that is applied to a gate terminal of the FET
Implementation Method 3
a time constant selector circuit with capacitors, enabling accurate detection of ambient light and subsequent measurement of desired light signals
Data Source
AI summary
An optical measurement system includes a photodetector coupled in series with a field effect transistor (FET) that is a part of a sample and hold circuit. When the sample and hold circuit is in a sampling mode of operation, a voltage bias is applied to the FET and the photodetector is exposed to ambient light, thus resulting in a first current flow through the photodetector. One of several components can be selected in the sample and hold circuit for obtaining a desired time constant. When the sample and hold circuit is subsequently placed in a hold mode of operation, a second current flows through the photodetector due to exposing of the photodetector to a combination of ambient light and light associated with an optical measurement. A portion of the second current that is attributable to the light associated with the optical measurement is used for executing the optical measurement.