Optical Proximity Sensor Self-Compensation for Ambient Light Crosstalk
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Solution Overview
Problem
Conventional optical proximity sensors in smartphones fail to effectively cancel ambient light and optical crosstalk noise, which affects distance calculation accuracy, and existing solutions either increase device thickness or require complex circuit topologies, making them unsuitable for portable devices.
Innovation Solution
An optical proximity sensor using light-to-frequency conversion technique, comprising a controlling and processing circuit, lighting and receiving units, digital-to-analog converters, and a light-to-digital conversion module, generates compensation current signals to cancel ambient light and crosstalk noise through an analog adder and pulse frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional optical sensing circuits or packaging housing structures are used to cancel optical crosstalk noise, then optical crosstalk noise cancellation is achieved, but ambient light noise cannot be canceled and device thickness increases
Solution Approach 1:
The patent extracts the optical barrier from the packaging housing structure and relocates it to the light receiving element. This allows the packaging housing to maintain a thin profile (0.75-1mm) while still providing optical crosstalk noise cancellation through the integrated barrier in the light receiving element structure.
Solution Approach 2:
The patent combines multiple functions into the light receiving element: it serves as both the light detection component and the optical barrier. By integrating the optical barrier directly into the light receiving element structure, the patent eliminates the need for separate optical barriers in the packaging housing, thereby reducing overall device thickness.
2Object-affected harmful factors
If optical barrier is added to packaging housing to block optical crosstalk, then optical crosstalk noise is canceled, but device weight increases and volume increases
Solution Approach 1:
The patent merges the optical barrier function with the light receiving element structure, eliminating the need for separate optical barrier components in the packaging housing. This integration reduces both the weight and volume of the overall device while maintaining optical crosstalk noise cancellation capability.
Solution Approach 2:
The patent employs a thin optical barrier integrated into the light receiving element structure rather than using thick rigid optical barriers in the packaging housing. This approach maintains the light weight and compact form factor required for portable devices while effectively blocking optical crosstalk.
3Object-affected harmful factors
If complex circuit topology is used to cancel optical crosstalk noise, then optical crosstalk noise is canceled, but ambient light noise cannot be canceled and device complexity increases
Solution Approach 1:
The patent converts the harmful effects of both optical crosstalk and ambient light into useful information by measuring them separately during calibration. The measured crosstalk and ambient light signals are stored as compensation values and subtracted from subsequent measurements, transforming these noise sources into correctable data that improves measurement accuracy.
Solution Approach 2:
The patent performs calibration measurements in advance to characterize and store compensation values for optical crosstalk and ambient light effects. These pre-measured compensation values are then used to correct subsequent distance measurements, eliminating the need for complex real-time noise cancellation circuits.
4Illumination intensity
If ambient light intensity is considered far greater than optical crosstalk, then ambient light dominates noise profile, but existing solutions fail to address both simultaneously
Solution Approach 1:
The patent converts the dominant ambient light noise into a measurable and correctable parameter by including it in the calibration process. The ambient light signal is measured during calibration and stored as a compensation value, allowing the system to subtract this large noise component from subsequent measurements, thereby achieving accurate distance measurement even in bright lighting conditions.
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 solution enables accurate removal of ambient light and optical crosstalk noise, improving distance calculation accuracy while maintaining a lightweight and compact design suitable for portable devices.
Implementation Method 1
a light receiving element 23 configured to receive a reflective light 32 reflected from the object 3 and generate a first current signal corresponding to the reflective light 32
Implementation Method 2
a light-to-frequency conversion module 121 configured to convert the current signal to a pulse frequency modulated signal
Data Source
AI summary
Disclosures of the present invention describe an optical proximity sensor, which is particularly designed to have functionality of canceling an ambient light noise and/or an optical crosstalk noise by using light-to-frequency conversion technique, and comprises: a controlling and processing circuit, a lighting unit, a light receiving unit, an analog adder, a first DAC unit, a second DAC unit, and a light-to-digital conversion (LDC) unit. In the controlling of the controlling and processing circuit, the first DAC unit and the second DAC unit would respectively generate a first compensation current signal and a second compensation current signal to the analog adder, such that a noise signal of ambient light and a noise signal of optical crosstalk existing in an optical current signal of object reflection light would be canceled by the two compensation current signals in the analog adder.