Optical Sensor Circuit Luminosity Correction via Time-Division AD
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Solution Overview
Problem
Current semiconductor integrated circuits for optical sensors face challenges in achieving high precision luminosity factor correction due to difficulties in securing precision with minute electric currents and conversion errors from using different AD converters for infrared and visible light measurements, especially when placed behind cover members that attenuate visible light and transmit infrared light.
Innovation Solution
A semiconductor integrated circuit with a luminosity factor correction unit that includes a first light receiving element with a specific spectral property for visible light and a second light receiving element with a different spectral property for infrared light, utilizing an AD conversion unit for time division conversion and a calculating unit to subtract digital signals, along with a multiplier and correction coefficient setting unit to adjust for accurate luminosity factor correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current mirror circuit is used for luminosity factor correction, then the correction can be performed, but precision is difficult to secure with respect to minute electric current
Solution Approach 1:
The patent replaces the current mirror circuit (analog system) with an AD conversion system that converts currents to digital signals. This substitution allows for more precise measurement and processing of minute electric currents through digital means, resolving the precision limitation of the analog current mirror approach.
Solution Approach 2:
The patent uses two photo diodes (PD1 and PD2) with different spectral properties to create copies of the light measurement process. By converting both measurements to digital signals and processing them through the same AD converter, the system can accurately compare and correct luminosity factors without the precision losses inherent in analog current mirroring.
2Productivity
If different AD converters are used for output currents of two photo diodes, then AD conversion can be performed, but conversion errors occur among digital signals due to variations among AD converters
Solution Approach 1:
The patent merges the AD conversion process by using a single AD converter for both photo diodes instead of separate converters. This is achieved through time-division multiplexing where the same converter processes signals from PD1 and PD2 alternately, ensuring consistent conversion characteristics and eliminating inter-converter variation errors.
Solution Approach 2:
The patent implements periodic action through time-division AD conversion, where the single AD converter alternates between converting signals from PD1 and PD2 in periodic time slots. This periodic switching ensures that both signals undergo identical conversion processes, eliminating systematic errors that would arise from using different converters.
3Adaptability or versatility
If the sensor is placed behind a cover member such as a panel, then design requirements are met, but the sensor receives much infrared light causing erroneous measurements
Solution Approach 1:
The patent implements feedback by using the measurement from PD2 (infrared-sensitive photo diode) to correct the measurement from PD1 (visible and infrared sensitive photo diode). The correction unit uses the infrared measurement as feedback to subtract the inappropriate infrared component from the visible light measurement, thereby correcting the luminosity factor error introduced by the cover member.
Solution Approach 2:
The patent introduces an intermediary correction unit that processes the measurements from both photo diodes. This correction unit acts as a mediator that combines the visible light measurement and infrared measurement to produce a corrected luminosity value, effectively removing the distorting effect of the cover member through mathematical correction.
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 solution enables high-precision luminosity factor correction, reducing erroneous measurements and improving the accuracy of illuminance detection under various light sources by controlling the relative sensitivity to infrared light, thereby enhancing the overall performance of the optical sensor.
Implementation Method 1
a first light receiving element (PD1) having a first spectral property; a second light receiving element (PD2) having a second spectral property
Data Source
AI summary
There is provided a semiconductor integrated circuit for an optical sensor for receiving environmental light through a cover member that attenuates visible light and transmits infrared light and a collecting lens, performing luminosity factor correction based on an amount of received light, and detecting an illuminance, wherein the semiconductor integrated circuit includes a first light receiving element having a first spectral property; a second light receiving element having a second spectral property; and a luminosity factor correction unit configured to perform the luminosity factor correction according to output of the first light receiving element and output of the second light receiving element, wherein the luminosity factor correction unit includes an AD conversion unit performed by time division on the output of the first light receiving element and the output of the second light receiving element, and a calculating unit subtracting digital signals obtained by the conversion.