Integrated Light-to-Digital Converter for High Dynamic Range Sensing
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Solution Overview
Problem
Light-to-digital converters in photoplethysmogram (PPG) and functional near-infrared spectroscopy (fNIRS) systems require high dynamic range while maintaining low power consumption, as the AC/DC ratio in PPG signals and the long light path in fNIRS systems demand high dynamic range exceeding 80 dB and 100 dB respectively, posing challenges for existing converters.
Innovation Solution
A light-to-digital converter design that incorporates a light-to-current converter, a current integrator with reset capability, and a counter, allowing for both signal readout and analog-to-digital conversion, reducing component count and power requirements by using a single component for transimpedance amplification, noise anti-aliasing, and digitalization, with a comparator to determine counter stopping points and a reference current source for accurate measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate readout frontend and high-resolution ADC components are used, then dynamic range is improved, but power consumption increases
Solution Approach 1:
The patent combines the readout frontend and ADC functions into a single integrated component. The integrator circuit performs both transimpedance amplification and analog-to-digital conversion in one unit, eliminating the need for separate high-resolution ADC components while maintaining the required dynamic range performance.
Solution Approach 2:
The integrator component is designed to perform multiple functions simultaneously: it acts as a transimpedance amplifier for signal conditioning, an anti-aliasing filter for noise reduction, and an ADC for digital conversion. This multi-functionality reduces the overall component count and power consumption while achieving the required measurement precision.
2Measurement precision
If multiple separate components are used for signal processing, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple signal processing functions into a single integrator component. Instead of using separate components for transimpedance amplification, anti-aliasing filtering, and ADC conversion, the integrator performs all these functions in one unit, reducing device complexity while maintaining signal accuracy through careful circuit design.
Solution Approach 2:
The integrator is designed as a universal component that handles multiple signal processing tasks. It provides transimpedance amplification to convert photodiode current to voltage, implements anti-aliasing filtering to reduce noise, and performs ADC conversion to digitize the signal, thereby reducing the overall component count while preserving measurement accuracy.
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 achieves a high dynamic range of 119 dB with significantly reduced power consumption, compared to systems using separate readout frontends and ADCs, while maintaining accuracy and simplicity, making it suitable for PPG and fNIRS applications.
Implementation Method 1
the light-to-current converter comprises a photodiode
Data Source
AI summary
A light-to-digital converter (2) comprises a light-to-current converter (10); a current integrator (4) with an integrator output (30) resettable to a baseline level; and a counter (18) with a digital output (26), wherein the light-to-current converter (10) is switchably connectable as a positive integration input to the current integrator (4), for, during a light-collecting phase (404-406), integrating a current from the light-to-current converter (10), the integrator output (30) starting from the baseline value and ending at a value to be digitized; a reference current source (14) is switchably connectable as a negative integration input to the current integrator (4), for, during a counting phase (406-408) subsequent to the light-collecting phase (404-406), integrating a reference current from the reference current source (14), the integrator output (30) starting from the value to be digitized and ending at the baseline value, the time spent integrating the reference current corresponding to the value to be digitized; and the counter (18) is configured for measuring the time.