Optical Sensor ADC Multiplexing for Chip Area Reduction
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Solution Overview
Problem
Existing optical sensors face challenges in achieving high accuracy and reducing cost and power consumption due to the need for multiple analog-to-digital converters (ADCs) and increased chip area, while also requiring separate measurements for different light types, which limits their size and efficiency.
Innovation Solution
An optical sensor design that includes a RGB light receiving portion and an other light receiving portion with distinct spectral sensitivity characteristics, utilizing three ADCs and switches to apply photocurrents from these portions to convert them into digital values, allowing for real-time measurement and correction of photocurrents, thereby reducing the number of ADCs and enhancing detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple ADCs are individually prepared for each light receiving portion, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
Multiple light receiving portions (RGB and other colors) share a single ADC through time-division multiplexing. The switch circuit alternately connects different light receiving portions to the same ADC, allowing one ADC to serve multiple photodetectors without requiring separate ADCs for each, thus reducing chip area while maintaining measurement capability
Solution Approach 2:
The single ADC is designed to universally handle photocurrents from multiple light receiving portions by being configurable to receive signals from different photodetectors at different times. This multi-functional ADC replaces multiple dedicated ADCs, reducing device complexity while preserving the ability to measure all light types
2Productivity
If multiple ADCs are individually prepared for each light receiving portion, then real-time measurement capability is improved, but power consumption increases
Solution Approach 1:
Multiple light receiving portions share a single ADC through time-division multiplexing. The switch circuit alternately connects different light receiving portions to the same ADC, allowing one ADC to serve multiple photodetectors without requiring separate ADCs, thus reducing power consumption while maintaining measurement capability
Solution Approach 2:
The system uses periodic switching to alternately connect different light receiving portions to the shared ADC. By rapidly switching between photodetectors in a periodic manner, the system maintains real-time measurement capability for all light types while the single ADC remains the only active converter, significantly reducing power consumption compared to having multiple simultaneously operating ADCs
3Measurement precision
If separate measurements are performed for different light types, then measurement precision is maintained, but measurement time increases
Solution Approach 1:
The switch circuit performs rapid periodic switching between different light receiving portions, connecting each to the shared ADC in turn. This fast periodic measurement cycle allows all light types to be measured in succession within a short time frame, maintaining measurement precision through sequential sampling while minimizing total measurement time
Solution Approach 2:
The measurement process continues without interruption by rapidly switching between light receiving portions. The shared ADC continuously converts photocurrents from different photodetectors in sequence, ensuring that measurement action is continuous and uninterrupted, thus reducing total measurement time while maintaining accuracy through persistent sampling
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 a highly accurate optical sensor with reduced semiconductor integration circuit size and cost, improved power efficiency, and enhanced detection accuracy of photocurrents by using a computation reference light receiving portion to calculate and correct photocurrent values from the other light receiving portions.
Implementation Method 1
a photodiode 3I, a photodiode 3B, a photodiode 3G, a photodiode 3R and a photodiode 3C are prepared for the infrared light receiving portion Ir, the blue light receiving portion BLUE, the green light receiving portion GREEN, the red light receiving portion RED and the environmental light receiving portion CLEAR, respectively
Data Source
AI summary
An optical sensor (10) includes a first switch (SW1) and a second switch (SW2), these switches are switched between a first step and a second step and thus the coupling of light receiving portions (photodiodes) and three analog-to-digital converters (ADCs) is switched. In the first step of the switch, photocurrents generated in a blue light receiving portion (BLUE), a green light receiving portion (GREEN) and a red light receiving portion (RED) are processed in real time. In the second step, photocurrents generated in an infrared light receiving portion (Ir), an environmental light receiving portion (CLEAR) and the green light receiving portion (GREEN) are processed. The photocurrents of the infrared light receiving portion (Ir) and the environmental light receiving portion (CLEAR) generated in the first step are calculated from a ratio of the two photocurrents measured in the green light receiving portion (GREEN).