Terminal Proximity Wake-Up Using Pulsed Time-of-Flight Sensing
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Solution Overview
Problem
Existing proximity detection systems in terminals, such as payment terminals, face challenges with detection distance variability due to environmental conditions, mechanical tolerances, and electronics component variations, requiring high currents that can damage the power circuit and are not energy-efficient.
Innovation Solution
A method using an RC circuit to feed a light-emitting diode (LED) with electrical pulses, combined with a photodiode to determine time-of-flight pulses, and a processing circuit to adjust detection distance thresholds, ensuring consistent detection beyond 40 cm while minimizing current draw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the detection distance is increased to more than 40 cm, then the terminal has sufficient time to wake up before user arrival, but high currents (more than 4 A) are required that exceed the PMIC capability (3 A) and can damage the power circuit
Solution Approach 1:
The patent applies periodic action by using pulsed illumination instead of continuous LED operation. The LED is activated in periodic pulses synchronized with time-of-flight measurement cycles, allowing the system to achieve high peak currents only momentarily during measurement windows. This periodic operation enables detection distances beyond 40 cm while keeping average current draw within the 3 A PMIC limit, as the high current pulses occur only during brief measurement intervals rather than continuously.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting LED pulse width, pulse frequency, and pulse amplitude based on detection requirements and power availability. By varying these parameters, the system can achieve sufficient peak power for long-distance detection (>40 cm) while maintaining average power consumption within the 3 A limit. The pulse duration and intensity are optimized to provide adequate detection range without overloading the PMIC.
2Length of stationary object
If the detection distance is increased to more than 40 cm, then early user detection is enabled, but the detection distance becomes highly variable due to environmental conditions, mechanical tolerances, and electronics component variations
Solution Approach 1:
The patent implements feedback through time-of-flight measurement, which provides a direct temporal reference for detection distance. By measuring the round-trip time of light pulses and using the known speed of light, the system calculates distance with high precision that is independent of environmental lighting conditions, photodiode sensitivity variations, or LED output changes. This feedback mechanism compensates for component tolerances and environmental factors, maintaining reliable and stable detection distance beyond 40 cm.
Solution Approach 2:
The patent replaces traditional optical intensity-based detection with time-of-flight measurement. Instead of relying on the intensity of reflected light (which varies with environmental conditions, clothing color, and component tolerances), the system measures the time delay of reflected light pulses. This substitution of measurement principle eliminates sensitivity to most environmental and component variations, providing stable and reliable detection distance independent of external factors.
3Length of stationary object
If the LED is fed with high currents to reach detection distance of 1 m, then sufficient detection range is achieved, but the power management integrated circuit (PMIC) that can supply only 3 A is overloaded
Solution Approach 1:
The patent uses periodic pulsed operation to deliver high peak currents to the LED only during brief measurement intervals, while keeping the average current within the PMIC's 3 A capability. The LED receives high current pulses (exceeding 4 A) only during short windows when distance measurement is performed, and remains off or operates at low current between pulses. This periodic action pattern allows achieving 1 m detection range without continuously overloading the PMIC, preventing power circuit damage while maintaining sufficient detection range.
Solution Approach 2:
The system performs preliminary action by pre-charging capacitors during low-current periods and then rapidly discharging them during measurement pulses. This allows the LED to receive high current pulses without requiring the PMIC to continuously supply excessive current. The energy is stored in advance and released in controlled pulses, protecting the PMIC from continuous overcurrent stress while still achieving the necessary peak power for long-distance detection.
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 provides a constant and reliable detection distance independent of environmental and component variations, reducing energy consumption and protecting the power circuit by limiting current draw.
Implementation Method 1
feeding a light emitting diode, LED, by electrical pulses... the LED illuminating a detection zone with light pulses
Implementation Method 2
capturing by a photodiode light pulses coming from the detection zone
Implementation Method 3
feeding a light emitting diode, LED, by electrical pulses, between an RC circuit connected to a voltage source
Data Source
Figure 1~3
Figure 4
AI summary
The present disclosure relates to a method for detecting a user (U1) approaching a terminal (T1) within a detection distance (D), the method comprising: feeding a LED, by electrical pulses, between an RC circuit connected to a voltage source and a first resistor connected to ground, the LED illuminating a detection zone with light pulses; capturing by a photodiode light pulses coming from the detection zone; determining a pulse count representative of a time-of-flight of a light pulse emitted by the LED and received by the photodiode; computing a count variation by subtracting a reference count from the pulse count, the reference count being determined when no object is present in the detection zone; comparing the count variation with a threshold corresponding to the detection distance; and triggering an operation when the count variation is lower than the first threshold.