Optical Measurement System Ambient Light Nullification
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Solution Overview
Problem
Existing optical measurement systems face challenges in accurately measuring ambient light, particularly in time-of-flight distance measurement systems, due to complexities in determining optimal sampling periods, leading to inadequate suppression of ambient light effects and compromised performance parameters such as signal-to-noise ratio (SNR) and dynamic range.
Innovation Solution
An optical measurement system incorporating a detector circuit, an ambient light suppression circuit, and a correlator circuit, where the ambient light suppression circuit uses a sample and hold mechanism to detect and nullify ambient light effects, and a current gain element to enhance SNR and sensitivity, while automatically regulating photodetector bias voltage for temperature and fabrication variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a long sampling period is used to detect ambient light, then measurement accuracy of ambient light is improved, but measurement delay increases and ambient light conditions may change during sampling
Solution Approach 1:
The patent implements periodic sampling of ambient light at multiple discrete time points within a measurement cycle. Instead of continuous or single-point sampling, the system performs repeated measurements at intervals, allowing it to capture ambient light variations while maintaining timing synchronization with the modulated light signal. This periodic approach resolves the contradiction by providing sufficient sampling density for accuracy without requiring excessively long continuous sampling periods that would cause delays.
Solution Approach 2:
The system performs preliminary ambient light measurements during specific time windows before the main distance measurement occurs. By pre-characterizing the ambient light conditions in the vicinity of the expected reflected signal arrival, the system prepares compensation data in advance, reducing the critical path delay while ensuring the ambient light measurement is sufficiently accurate for the subsequent distance calculation.
2Productivity
If a short sampling period is used to reduce measurement delay, then response speed is improved, but ambient light measurement accuracy deteriorates
Solution Approach 1:
The system uses periodic sampling at optimized intervals that are short enough to maintain fast response but frequent enough to capture ambient light characteristics. The sampling frequency is specifically tuned to the modulated light frequency, allowing accurate ambient light measurement through correlation processing even with brief sampling windows. This resolves the speed-accuracy tradeoff by leveraging the periodic nature of the measurement signal.
Solution Approach 2:
The system incorporates feedback mechanisms where preliminary ambient light measurements inform the timing and duration of subsequent measurements. Based on the detected ambient light level and its temporal variations, the system dynamically adjusts sampling parameters to achieve sufficient accuracy with minimal sampling time, thereby maintaining fast response while improving measurement precision when needed.
3Measurement precision
If signal amplification is used to improve receiver sensitivity, then SNR is improved, but dynamic range is compromised due to overload thresholds
Solution Approach 1:
The patent implements dynamic gain control and adaptive signal processing that adjusts amplification levels based on the detected signal strength and ambient light conditions. The system can switch between different gain stages and processing modes to handle both weak distant signals requiring high sensitivity and strong nearby signals requiring full dynamic range. This dynamic adaptation resolves the contradiction by providing high receiver sensitivity only when needed for weak signals while maintaining full dynamic range capability for stronger signals.
Solution Approach 2:
The system changes processing parameters such as integration time, gain level, and correlation window duration based on the measured signal characteristics and ambient light level. By adaptively adjusting these parameters, the system optimizes receiver sensitivity for weak signals while preventing saturation for strong signals, thereby maintaining both high SNR performance and full dynamic range across varying measurement conditions.
4Reliability
If ambient light suppression circuitry is added to eliminate ambient light effects, then measurement robustness is improved, but device complexity increases
Solution Approach 1:
The patent uses correlation processing as an intermediary technique to separate the modulated reflected signal from the ambient light background. Instead of adding complex hardware filters or suppression circuits, the system modulates the transmitted light at a specific frequency and uses synchronous detection to extract only the signal components at that frequency. This mathematical intermediary approach effectively suppresses ambient light effects while adding minimal circuit complexity, as it leverages existing signal processing capabilities rather than requiring additional hardware blocks.
Solution Approach 2:
The system replaces potential hardware-based ambient light suppression mechanisms (such as optical filters, mechanical shutters, or complex circuitry) with software-based correlation processing and digital signal techniques. By substituting electronic/mathematical processing for mechanical or hardware solutions, the system achieves robust ambient light rejection with minimal additional device complexity, leveraging the computational power of existing processors rather than adding dedicated suppression hardware.
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 system effectively suppresses ambient light, improves receiver sensitivity, and operates over a wide dynamic range, ensuring accurate measurements and high SNR, even in environments with varying ambient light conditions.
Implementation Method 1
a photodetector incorporated into a digital camera (in the form of an image sensor) can be used to measure light intensities
Implementation Method 2
the ambient light suppression circuit uses a sample and hold mechanism to detect and nullify ambient light effects
Implementation Method 3
a current gain element to enhance SNR and sensitivity
Implementation Method 4
The time delay between transmission of the light beam and reception of the reflected light is used to calculate the distance between the measurement system and the target object
Data Source
AI summary
An optical measurement system is provided for performing time-of-flight distance measurement with ambient light suppression. The system has a detector circuit that includes a photodetector and an additional current gain element that amplifies the photocurrent produced by the photodetector. Placement of the additional current gain element near the photodetector allows low-power optical signals to be detected without amplifying noise from sources of the system that are outside of the detector circuit, thereby allowing a high signal-to-noise ratio to be achieved. Embodiments of the system include circuitry that automatically regulates the bias voltage of the photodetector to compensate for temperature and for fabrication process variations.