BJT Pixel Circuit Ambient Light Cancellation
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Solution Overview
Problem
Conventional BJT pixel circuits struggle to effectively cancel the influence of strong ambient light, leading to difficulties in detecting objects using proximity sensors, as the difference between differential signals becomes too small to distinguish the activation and deactivation of system light sources under intense ambient conditions.
Innovation Solution
The BJT pixel circuit employs two shutter switches and storage capacitors to generate distinct voltage signals corresponding to light-on and light-off levels, allowing for differential operation by an integrator to isolate system light signals from ambient light, reducing the need for additional ambient image frames and sampling, and enhancing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital subtraction operation is performed on differential signals to cancel ambient light influence, then ambient light cancellation is achieved, but the detection precision deteriorates under strong ambient light conditions
Solution Approach 1:
The patent segments the light measurement process into two distinct phases: a first exposure phase capturing system light plus ambient light, and a second exposure phase capturing only ambient light. By separating these measurements into distinct time periods with controlled shutter operations, the system can independently measure and subsequently subtract ambient light effects, maintaining detection precision even under strong ambient light conditions.
Solution Approach 2:
The patent performs preliminary measurement of ambient light in a second exposure phase before the actual system light measurement. By capturing the ambient light level first (when the system light source is off), the system prepares the reference data needed for accurate subtraction during the subsequent system light measurement phase, ensuring that ambient light effects are properly compensated without compromising detection precision.
2Measurement precision
If multiple sampling operations are performed to improve detection accuracy, then measurement precision is improved, but the operation time increases
Solution Approach 1:
The patent implements continuous useful action by performing both the first exposure (system light + ambient light) and second exposure (ambient light only) operations within a single integrated frame period. The dual storage capacitor architecture allows simultaneous or sequential capture of both measurement types without requiring additional frame cycles, maintaining continuous operation while achieving accurate ambient light cancellation and improving detection precision efficiently.
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
This solution enables accurate detection of objects and gestures under strong ambient light conditions, improving the signal-to-noise ratio and reducing sampling requirements, thereby enhancing the functionality of proximity sensors and gesture recognition systems.
Implementation Method 1
a photodiode 31, a BJT transistor 33
Data Source
AI summary
There is provided a BJT pixel circuit including a BJT transistor, a photodiode, a first storage capacitor and a second storage capacitor. The first storage capacitor is configured to discharge, via the BJT transistor, to a first output voltage in a first exposure time of the photodiode. The second storage capacitor is configured to discharge, via the BJT transistor, to a second output voltage in a second exposure time of the photodiode.