Optical Sensor High-Pass Filter Circuit for Ambient Light Rejection
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Solution Overview
Problem
Existing optical sensing devices face challenges in accurately detecting light reflected from input objects in the presence of high ambient light, such as sunlight, due to interference from ambient light signals with slow rise and fall times.
Innovation Solution
The implementation of a processing system for an optical sensing device that includes receiver circuitry with high-pass filter circuitry and a determination module, utilizing a reset switch to reset a feedback capacitor based on a reset signal frequency corresponding to the drive signal frequency, allowing for the generation of a high-pass filtered signal and subsequent light measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ambient light filtering is not applied, then the device can detect all light signals including reflected light from input objects, but the detection accuracy deteriorates due to interference from high ambient light signals with slow rise and fall times
Solution Approach 1:
The patent applies periodic action by using a reset signal with a frequency corresponding to the drive signal frequency to periodically reset the feedback capacitor. This periodic resetting creates a high-pass filter effect that allows the circuit to respond only to rapid changes in light signals (such as reflected light from input objects) while rejecting slow-varying ambient light interference, thereby improving detection accuracy in high ambient light conditions
Solution Approach 2:
The patent changes the temporal parameter of the feedback capacitor by periodically resetting it with a reset signal. This parameter change transforms the capacitor's behavior from continuously integrating all light signals to selectively responding only to rapid changes, effectively filtering out ambient light with slow rise and fall times while preserving the detection of reflected light signals
2Measurement precision
If a reset switch is added to the high-pass filter circuitry, then the filtering of ambient light signals is improved, but the device complexity increases
Solution Approach 1:
The reset switch in the high-pass filter circuitry serves multiple functions: it periodically discharges the feedback capacitor to create the high-pass filtering effect, it synchronizes with the drive signal frequency to maintain consistent filtering characteristics, and it enables the circuit to operate reliably in high ambient light conditions. By consolidating these functions into a single component controlled by a reset signal, the patent achieves effective ambient light filtering without proportionally increasing circuit complexity
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
Enables accurate detection and measurement of light reflected from input objects even in the presence of high ambient light conditions, effectively filtering out ambient light signals with slow rise and fall times, thereby improving the device's sensitivity and accuracy.
Implementation Method 1
receiver circuitry configured to receive a resulting signal from a photodetector. The resulting signal corresponds to light emitted by a light source
Implementation Method 2
The high-pass filter circuitry comprises an input capacitor, a feedback capacitor, and a reset switch
Data Source
AI summary
A processing system for an optical sensing device may comprise receiver circuitry and a determination module. The processing system may also include drive circuitry configured to drive a light source to emit light. The receiver circuitry is coupled to a photodetector, and the receiver circuitry is configured to acquire a resulting signal from the photodetector, and generate a measurement of light received by the photodetector based on the resulting signal. The receiver circuitry includes high-pass filter circuitry configured to high-pass filter the resulting signal to generate a high-pass filtered signal based. The determination module is configured to generate a light measurement based on the high-pass filtered signal.