Optoelectronic Module Spurious Reflection Compensation
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Solution Overview
Problem
Time-of-flight (TOF) sensors in handheld devices face accuracy issues due to spurious signals from smudges or dirt on the transmissive window, leading to inaccurate distance calculations.
Innovation Solution
The development of optoelectronic modules with dedicated spurious-reflection detection pixels and circuitry to differentiate and correct for spurious reflections, using light redirecting elements and absorbing regions to isolate and redirect light from smudges, and employing processing circuitry to compensate for thermal drift and phase shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spurious-reflection detection pixels and correction circuitry are added to the TOF sensor, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The sensor array is segmented into different functional regions: regular demodulation pixels for distance measurement and dedicated spurious-reflection detection pixels for detecting reflections from smudges or contaminants. This segmentation allows the system to separately measure and correct spurious reflections, improving distance calculation accuracy without requiring a complete redesign of the sensor architecture.
Solution Approach 2:
A reflector is introduced as an intermediary optical element positioned between the cover glass and the sensor. The reflector redirects light that has reflected off the cover glass (including spurious reflections from smudges) toward the spurious-reflection detection pixels. This intermediary element enables the separation of spurious reflection signals from object reflection signals, allowing for accurate compensation.
2Measurement precision
If light redirecting elements and absorbing regions are added to isolate spurious reflections, then measurement precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
The passive optical element is designed with spatially varying properties: light absorbing regions are placed in specific locations to block direct emitter light from reaching certain pixels, while light redirecting elements are positioned to guide spurious reflections toward detection pixels. This local differentiation of optical properties enables precise signal separation without requiring the entire optical system to meet extremely tight manufacturing tolerances.
Solution Approach 2:
The spurious-reflection detection pixels capture a copy of the spurious reflection signal that is separate from the main detection path. By creating this duplicate measurement path specifically for spurious reflections, the system can subtract the spurious signal from the total measurement, improving accuracy without requiring perfect isolation in the main path.
3Reliability
If dedicated spurious-reflection detection pixels are implemented, then reliability of distance measurement is improved, but productivity of the device decreases
Solution Approach 1:
The optoelectronic emitter uses intensity modulation at specific frequencies, and the sensor performs demodulation at these frequencies to distinguish between different light sources. By using periodic modulation and synchronous detection, the system can separate object reflections from spurious reflections based on their different modulation characteristics, improving reliability without requiring additional measurement cycles.
Solution Approach 2:
The correction circuitry uses signals from the spurious-reflection detection pixels to calculate and subtract the spurious reflection component from the total signal measured by the demodulation pixels. This feedback-based correction process automatically compensates for spurious reflections in real-time, improving measurement reliability without requiring manual intervention or repeated measurements.
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
Enhances the accuracy of distance calculations by effectively distinguishing and correcting for spurious reflections, improving the reliability of optical signal detection in TOF systems.
Implementation Method 1
a light emitter to generate light to be emitted from the module
Implementation Method 2
spatially distributed light sensitive elements arranged to detect light from the emitter that is reflected by an object outside the module
Implementation Method 3
One or more light absorbing regions are provided in or on the second passive optical element and are substantially non-transparent to light at a wavelength emitted by the light emitter
Implementation Method 4
a reflector to direct a spurious light reflected by a smudge, a transmissive cover or other component to the dedicated spurious-reflection detection pixels
Data Source
AI summary
An optoelectronic module including a light emitter to generate light to be emitted from the module; a plurality of spatially distributed light sensitive elements arranged to detect light from the emitter that is reflected by an object outside the module; and one or more dedicated spurious-reflection detection pixels.