LED Sensor Cross-Talk Cancellation With On-Chip ADC-DAC Feedback
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Solution Overview
Problem
LED-based biometric optical sensors face challenges with cross talk, latency, and power consumption, which affect their dynamic range and accuracy in measuring vital signs.
Innovation Solution
The proposed solution involves initializing a DAC value and determining if the ADC operates within a predetermined range. When the ADC is within range, a conversion is initiated at a first ADC resolution, and the DAC value is incrementally changed when the ADC is not within range to maintain optimal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If off-chip microcontroller with feedback algorithm is used to cancel cross talk, then cross talk cancellation capability is improved, but latency increases to a fraction of a second
Solution Approach 1:
The patent integrates the microcontroller and feedback algorithm onto the same chip as the ADC and DAC, creating a unified on-chip system. This merging eliminates the off-chip communication delays and feedback loop latency, reducing the cross-talk cancellation latency from a fraction of a second to within the same sampling cycle, while maintaining the full feedback cancellation capability.
Solution Approach 2:
The patent introduces an on-chip intermediary processing unit that receives ADC output and directly generates DAC input within the same chip. This intermediary eliminates the external microcontroller bottleneck, enabling real-time cross-talk cancellation by mediating the feedback signal generation internally, thus reducing latency while preserving cancellation effectiveness.
2Use of energy by moving object
If low sample rate is used to minimize power consumption, then power consumption is reduced, but latency of feedback loop increases
Solution Approach 1:
The patent implements a dynamic on-chip feedback system that can operate at varying speeds independent of the main sampling rate. The on-chip microcontroller can process feedback signals and adjust DAC values dynamically within each sampling cycle, allowing the system to maintain low power consumption at low sample rates while eliminating feedback loop latency through instantaneous on-chip processing.
Solution Approach 2:
The patent performs preliminary cross-talk cancellation calculations on-chip before the actual sampling cycle completes. By pre-calculating the necessary DAC adjustments within the same chip during the sampling process itself, the system eliminates feedback latency without requiring increased sample rates, thus maintaining low power consumption while achieving real-time cancellation.
3Measurement precision
If high resolution ADC conversion is always used, then measurement precision is improved, but power consumption and conversion time increase
Solution Approach 1:
The patent dynamically changes the ADC resolution parameter based on the operating conditions and cross-talk levels. The on-chip microcontroller monitors the ADC output and adjusts the DAC input to optimize the signal range, allowing the system to use lower ADC resolution when cross-talk is minimal (reducing power consumption) while maintaining high effective precision when needed through active cross-talk cancellation.
Solution Approach 2:
The patent applies partial cross-talk cancellation by using a simplified on-chip algorithm that achieves sufficient cancellation without requiring full high-resolution processing at all times. By applying just enough cancellation to bring the signal within the optimal ADC range, the system achieves adequate measurement precision with reduced power consumption compared to always using maximum resolution conversion.
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 approach reduces unwanted crosstalk, latency, and power consumption, thereby enhancing the overall performance and accuracy of LED-based biometric sensors.
Implementation Method 1
shining green light and red light generated by LED light sources onto the person's skin
Implementation Method 2
measuring light reflected from the skin using a photodiode
Data Source
AI summary
Aspects of the present disclosure provide methods and apparatuses for operating an analog-to-digital converter. A method in accordance with an aspect of the present disclosure may comprise initializing a digital-to-analog converter (DAC) value of a DAC, determining whether an analog-to-digital converter (ADC) operates within a predetermined range based on an input to the DAC, initiating a conversion at a first ADC resolution when the ADC is operating within the predetermined range, and incrementally changing the DAC value when the ADC is not operating within the predetermined range.