Proximity Sensor ADC Feedback for Ambient Light Rejection
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Solution Overview
Problem
Conventional IR proximity sensors for handheld devices face challenges in ambient light rejection, leading to false triggering or failure to detect objects due to strong ambient light interference, and existing solutions like transimpedance amplifiers require large components and are slow.
Innovation Solution
A proximity sensor system incorporating a photodiode, analog-to-digital converter with analog-to-digital-to-analog feedback, and a controller to selectively drive a light source, allowing for digital output with majority ambient light rejection, using an M-bit ADC and N-bit ADC with up-down counter for improved signal processing and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large sensor area and special package with narrow band-pass filter are used to improve signal-to-noise ratio, then ambient light rejection is improved, but device size and complexity increase
Solution Approach 1:
The patent changes the operating parameters by using dual-wavelength detection and temporal modulation. The sensor measures at two different wavelengths (signal wavelength and reference wavelength) and processes signals in time domain, achieving ambient light rejection without requiring narrow band-pass filters or large sensor areas. This parameter-based approach replaces structural complexity with computational simplicity.
Solution Approach 2:
The patent replaces the mechanical/optical filtering approach (narrow band-pass filters and large sensor areas) with an electrical/digital processing approach. By using dual-wavelength measurement and digital signal processing to subtract ambient light components, the system achieves the same ambient light rejection function without physical filters, thereby reducing device complexity.
2Measurement precision
If high current is used to drive the IR LED to emit stronger IR light signal, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic modulation of the IR LED at specific frequencies and uses synchronous detection to extract the modulated signal. This periodic action allows the system to achieve high signal-to-noise ratio with lower average current by concentrating the signal energy in time domain, thereby reducing overall power consumption compared to continuous high-current operation.
Solution Approach 2:
The patent uses feedback through dual-wavelength measurement where the reference wavelength channel provides information about ambient light conditions. This feedback mechanism allows the system to adaptively compensate for ambient light variations, enabling lower drive currents while maintaining signal-to-noise ratio, thus reducing power consumption.
3Measurement precision
If transimpedance amplifier with RC network is used to reject ambient light, then ambient light rejection is improved, but chip area increases due to large resistor and capacitor
Solution Approach 1:
The patent replaces the analog RC network approach with digital signal processing. Instead of using large physical resistors and capacitors for ambient light rejection, the system uses dual-wavelength measurement and digital subtraction techniques. This substitution of analog components with digital processing dramatically reduces the required chip area while maintaining or improving ambient light rejection performance.
4Measurement precision
If transimpedance amplifier with active feedback loop is used to reject ambient light, then ambient light rejection is improved, but operating speed decreases
Solution Approach 1:
The patent uses periodic modulation of the IR LED and synchronous detection at the same frequency. This periodic action enables the system to achieve fast response by locking onto the modulated signal frequency, avoiding the slow response characteristics of active feedback loops. The temporal modulation approach allows rapid ambient light rejection without sacrificing operating speed.
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 enhances signal dynamic range and sensitivity, reducing ambient light interference and enabling accurate proximity detection with faster operation and smaller chip size, suitable for low-power handheld device applications.
Implementation Method 1
The PD converts the reflected light, as well as ambient light, to a current going to a resistor connected in parallel with the photodiode
Implementation Method 2
an infrared (IR) light emitting diode (LED)... The IR light emitted from the IR LED
Data Source
AI summary
In accordance with an embodiment, a proximity sensor includes a driver, a photodiode (PD), an analog-to-digital converter (ADC) with analog-to-digital-to-analog (ADA) feedback, and a controller. The driver is adapted to selectively drive a light source. The photodiode (PD) is adapted to produce a photodiode current signal (Idiode) indicative of an intensity of light detected by the PD, where the light detected by the PD can include ambient light and/or light transmitted by the light source that was reflected off an object proximate the PD. The controller is adapted to control the driver and the ADC with ADA feedback. A digital output of the ADC with ADA feedback is indicative of a proximity of an object to the PD with at least a majority of the ambient light detected by the PD rejected.