Image Sensor Pixel Circuit Photon Detection
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Solution Overview
Problem
Image sensors face challenges in accurately detecting the presence or absence of photons due to difficulties in inputting low voltage signals and generating offset voltages across all pixels, particularly with capacitive coupling and high sensitivity requirements.
Innovation Solution
An image sensor design incorporating a pixel circuit that generates signal and reset voltages, a capacitor to retain reset voltage, and comparators to amplify and determine voltage differences, with optional buffer amplifiers to expand dynamic range and reduce impedance, enabling accurate photon detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive coupling is used to input signals in high sensitivity sense circuits, then sensitivity is improved, but input voltage is lowered making accurate detection difficult
Solution Approach 1:
A buffer amplifier is introduced as an intermediary component between the pixel circuit and the sense circuit. This buffer amplifier has high input impedance that does not lower the input voltage from the pixel circuit, while providing sufficient drive capability for subsequent amplification stages, thus resolving the voltage level problem while maintaining sensitivity
Solution Approach 2:
The patent replaces direct capacitive coupling with a voltage buffer amplification system. Instead of relying solely on capacitive coupling to transfer the signal, an active buffer amplifier is used to transfer the voltage signal while maintaining its level, substituting the passive capacitive coupling mechanism with an active electronic system
2Measurement precision
If offset voltage is generated for each pixel individually, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a common offset voltage generation circuit that serves all pixels in the array. This universal offset generation approach eliminates the need for individual offset circuits in each pixel, reducing device complexity while still providing the necessary offset compensation for accurate detection across the entire sensor array
Solution Approach 2:
Multiple offset voltage generation functions are merged into a single common circuit that serves all pixels. By combining what would otherwise be distributed individual circuits into one shared resource, the patent reduces overall device complexity while maintaining the functional capability to provide offset compensation
3Measurement precision
If high conversion efficiency pixels are used, then sensitivity is improved, but signal voltage becomes very low requiring complex amplification
Solution Approach 1:
The buffer amplifier is positioned immediately after the pixel circuit to perform preliminary voltage buffering before the signal enters the main amplification and detection stages. This preliminary action prevents signal degradation and maintains voltage levels throughout subsequent processing, simplifying the overall amplification circuit design
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 configuration allows for accurate detection of photon presence or absence with a simple setup, improving sensitivity and reducing impedance, thereby enhancing the image sensor's performance.
Implementation Method 1
a pixel circuit that generates as an input voltage a signal voltage by photoelectrically converting light when the light is incident
Data Source
AI summary
Presence or absence of a photon is accurately detected in an image sensor with a simple configuration. A pixel circuit generates as an input voltage a signal voltage by photoelectrically converting light when the light is incident, and generates as the input voltage a predetermined reset voltage when light is not incident. A capacitor retains the predetermined reset voltage as a retained voltage. An amplification comparator amplifies a voltage difference between the input voltage and the retained voltage. A detection comparator outputs a result of determining whether or not the amplified voltage difference is higher than a predetermined value, as a detection signal indicating detected presence or absence of light incidence.