Monolithic CMOS Proximity Sensor for Ambient Light Rejection
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Solution Overview
Problem
Conventional IR proximity sensors are unsuitable for cell-phone and handheld-device applications due to their large size, high power consumption, and inability to effectively separate reflected IR light from ambient light, leading to a low signal-to-noise ratio.
Innovation Solution
A monolithic low-cost and low-power IR proximity sensor using a CMOS-integrated photo-diode, an analog-to-digital converter, and an IR LED driver that selectively drives an external IR LED, allowing for direct digital conversion of photo-current and subtraction of ambient light to isolate the IR light reflected from objects, thereby improving sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional IR proximity sensors are used, then proximity detection function is provided, but the sensor size is large and power consumption is high
Solution Approach 1:
The patent integrates the photo-diode, analog-to-digital converter, and IR LED driver onto a single monolithic CMOS integrated circuit. This consolidation merges multiple discrete components into one unified device, dramatically reducing the overall sensor size and minimizing the number of external components required, thereby solving the contradiction between providing full proximity detection functionality and reducing device footprint and power consumption.
Solution Approach 2:
The monolithic CMOS integrated circuit performs multiple functions: it detects reflected IR light, converts the signal to digital format, drives the IR LED, and compensates for ambient light interference. By making the sensor universal and multi-functional, the design eliminates the need for separate discrete components for each function, reducing both size and power consumption while maintaining reliable proximity detection.
2Reliability
If conventional IR proximity sensors are used, then proximity detection is possible, but the sensor area is large
Solution Approach 1:
The patent integrates the photo-diode, analog-to-digital converter, and IR LED driver onto a single monolithic CMOS integrated circuit. This consolidation merges multiple discrete components into one unified device, dramatically reducing the overall sensor size and minimizing the number of external components required, thereby solving the contradiction between providing full proximity detection functionality and reducing device footprint and power consumption.
Solution Approach 2:
The design embeds the analog-to-digital converter and driver circuits directly within the CMOS integrated circuit substrate, nesting multiple functional blocks within a compact hierarchical structure. This nesting approach allows complex functionality to be packed into a minimal area, enabling reliable proximity detection with a significantly reduced sensor footprint suitable for mobile devices.
3Reliability
If conventional IR proximity sensors are used, then basic proximity sensing is achieved, but the sensor cannot effectively separate reflected IR light from ambient light resulting in low signal-to-noise ratio
Solution Approach 1:
The IR LED is driven in periodic pulsed mode rather than continuously, emitting light only during specific time intervals. The analog-to-digital converter samples the photo-diode output synchronously with these pulses, capturing signals only when the IR LED is active. This periodic action creates a time-division multiplexing scheme that naturally separates the reflected IR light signals from continuous ambient light, dramatically improving the signal-to-noise ratio while maintaining basic proximity sensing functionality.
Solution Approach 2:
The analog-to-digital converter continuously monitors and subtracts the ambient light level from the total detected signal, even as ambient conditions change. This continuous compensation action ensures that the useful reflected IR light signal remains isolated from ambient interference throughout operation, maintaining high measurement precision and signal-to-noise ratio throughout the sensing process.
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 high sensitivity for proximity sensing even in high ambient light conditions, with reduced power consumption and smaller size, making it suitable for cell-phone and handheld-device applications.
Implementation Method 1
The PD, which produces a current signal indicative of the intensity of light detected by the PD
Implementation Method 2
The driver selectively drives a light source, e.g., an infrared (IR) light emitting diode (LED)
Data Source
AI summary
In an embodiment, a proximity sensor includes a driver, a photo-diode (PD) and an analog-to-digital converter (ADC). The proximity sensor can also include a controller to control the driver. The driver selectively drives a light source, e.g., an infrared (IR) light emitting diode (LED). The PD, which produces a current signal indicative of the intensity of light detected by the PD, is capable of detecting both ambient light and light produced by the light source that is reflected off an object. The ADC receives one or more portion of the current signal produced by the PD. The ADC produces one or more digital output that can be used to estimate the proximity of an object to the PD in a manner that compensates for ambient light detected by the PD and transient changes to the detected ambient light.