Proximity Sensing Circuit Using Double Sampling Under Displays
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Solution Overview
Problem
Optical proximity sensors installed under smartphone displays face challenges in detecting infrared light due to intensity reduction as it passes through the display, leading to increased power consumption and noise when trying to overcome this issue by increasing output intensity or sensor area.
Innovation Solution
A semiconductor device with a bias generating circuit, current source, signal conversion circuit, analog-to-digital converter, and driving circuit that uses a silicon nanowire sensing element and VCSEL light emitting element, employing correlated double sampling and single-slope ADC techniques to enhance noise reduction and proximity sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output intensity of infrared light is increased to overcome display attenuation, then the sensing capability is improved, but power consumption increases
Solution Approach 1:
The patent changes the parameter of bias voltage applied to the photodetector to optimize its sensitivity. By adjusting the bias voltage parameter, the sensor achieves higher detection sensitivity without requiring increased light emission intensity, thus resolving the contradiction between sensing capability and power consumption.
2Measurement precision
If the area of the optical sensor is increased to improve detection sensitivity, then the sensing capability is improved, but noise increases
Solution Approach 1:
The patent optimizes the bias voltage parameter to enhance the photodetector's sensitivity, allowing for improved detection capability without increasing sensor area. This parameter optimization enables high sensitivity while maintaining low noise levels by operating the sensor in an optimal voltage regime.
Solution Approach 2:
The patent replaces physical enlargement of sensor area with electrical parameter optimization (bias voltage adjustment). Instead of mechanically increasing sensor size to improve sensitivity, the system uses electrical parameter tuning to achieve the same effect without the associated noise penalties.
3Measurement precision
If the bias voltage is increased to improve signal detection, then the sensing accuracy is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic bias voltage sampling that optimizes the voltage parameter for signal detection accuracy. By sampling and adjusting the bias voltage parameter based on operating conditions, the system achieves high detection accuracy while minimizing power consumption through parameter optimization rather than continuous high voltage application.
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 effectively reduces noise and maintains sensitivity for proximity detection while minimizing power consumption by converting sensing currents into digital values using correlated double sampling and single-slope ADC methods, improving the accuracy and efficiency of proximity sensing.
Implementation Method 1
An optical proximity sensor detects proximity by emitting infrared light and detecting infrared light reflected from an object
Implementation Method 2
emitting infrared light and detecting infrared light reflected from an object
Implementation Method 3
a silicon nanowire sensing element
Data Source
AI summary
A semiconductor device includes a signal conversion circuit configured to convert a sensing current provided from a sensing element into a sensing voltage; an analog-to-digital converter (ADC) configured to convert the sensing voltage to a digital value; and a driving circuit configured to drive a light emitting element, wherein the ADC generates a digital value corresponding to proximity to an object by performing a primary operation comparing a ramp signal varying with time and the sensing voltage while the light emitting element is not driven and a secondary operation comparing the ramp signal and the sensing voltage while the light emitting element is driven.