Photodetector Sensitivity Control With Nonlinear Light Pulses

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Solution Overview

Problem

Existing optical measurement systems for detecting blood oxygenation and blood volume levels have low electrical-to-optical efficiency, particularly when generating narrow optical pulses at high repetition rates, which affects battery life and measurement accuracy.

Innovation Solution

The implementation of a control circuit that drives a light source with a current pulse having a non-linear rise and a decline from maximum output to zero within a threshold percentage of the total pulse duration, optimizing the electrical-to-optical efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If narrow optical pulses with high repetition rate are generated, then measurement accuracy and time resolution are improved, but electrical-to-optical efficiency deteriorates and power consumption increases

Engineering Contradiction:

Improvetime-of-arrival resolutionVSAvoidelectrical-to-optical efficiency

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The control circuit dynamically adjusts the drive current waveform characteristics (rise time, fall time, peak current) to optimize the balance between pulse width, repetition rate, and electrical-to-optical efficiency. By making the drive signal adaptive rather than fixed, the system can maintain high measurement precision while reducing power consumption.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent optimizes specific parameters of the drive current pulse including rise time (1-10 ns), fall time (1-10 ns), and peak current (10-100 mA) to achieve narrow optical pulses at high repetition rates while improving electrical-to-optical efficiency. These parameter adjustments allow the laser diode to operate more efficiently under pulsed conditions.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If high repetition rate optical pulses are generated, then productivity and data acquisition rate are improved, but power dissipation increases and battery life decreases

Engineering Contradiction:

Improvedata acquisition rateVSAvoidpower dissipation

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The system uses periodic pulsed operation with optimized duty cycle to achieve high data acquisition rates while minimizing average power dissipation. By concentrating optical energy into narrow pulses separated by rest periods, the laser diode can operate at high repetition rates (1 MHz or higher) without continuous power consumption, thereby extending battery life.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The control circuit maintains continuous data acquisition through high repetition rate pulsing, ensuring no useful measurement time is lost while keeping the average power consumption low. The pulsed operation allows the system to remain in a ready state without continuous power dissipation.

Inventive Principle:

Principle #20Continuity of useful action

3Device complexity

If conventional control circuits are used to drive laser diodes, then device complexity is minimized, but electrical-to-optical efficiency and light source parameter stability deteriorate

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidlight source parameter stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The control circuit incorporates dynamic adjustment capabilities for drive current waveform parameters including rise time, fall time, and peak current. This dynamic control stabilizes the laser diode operating point during pulsed operation, reducing parameter drift and improving measurement reliability while maintaining reasonable circuit complexity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses feedback from the photodetector to monitor and adjust the drive current waveform characteristics. This closed-loop control ensures stable light source parameters by compensating for variations in laser diode characteristics, temperature effects, and aging, thereby improving reliability without significantly increasing circuit complexity.

Inventive Principle:

Principle #23Feedback

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 enhances the efficiency of the control circuits, leading to improved battery life, reduced power dissipation, and more stable light source parameters, resulting in more accurate measurements and better metrics for mental states and physiological conditions.

Implementation Method 1

a photodetector configured to generate a photodetector output pulse in response to detecting a photon of the light

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

a light source configured to emit a light pulse directed at a target... a control circuit configured to drive the light source with a current pulse

Methodology Applied

Scientific EffectLight Emitting Diode: Light Emitting Diode

Data Source

PatentUS12235154B2Maintaining consistent photodetector sensitivity in an optical measurement system

Publication Date: 2025.02.25 HI LLC

AI summary

An illustrative optical measurement system includes a light source configured to emit a light pulse directed at a target. The optical measurement system further includes a control circuit configured to drive the light source with a current pulse comprising a non-linear rise, and a decline from a maximum output to zero having a duration within a threshold percentage of a total pulse duration of the current pulse.