Display Image Sensor Pixel With Cascode Amplifier for Low-Noise Sensing
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Solution Overview
Problem
Existing image sensors in display devices face challenges in reducing noise and improving signal-to-noise ratio (SNR), especially in high-resolution and large-sized applications, due to the vulnerability of sensing signals to noise from parasitic capacitors and the need for separate light sources, which affects image quality and sensitivity.
Innovation Solution
The proposed image sensor design includes a sensor pixel structure with a light-sensing element, storage capacitor, and a multistage cascode amplifier with transistors, where the amplifier outputs a sensing signal corresponding to the voltage of the node, and the use of internal light from display pixels as a light source, reducing noise and enhancing SNR by amplifying signals within the sensor pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional image sensor design is used, then the structure is simple, but the noise is high and signal-to-noise ratio is poor
Solution Approach 1:
The sensor pixel is divided into multiple functional regions: a light-sensing element for generating photocharges, a storage capacitor for holding charges, and a multi-stage amplifier for signal amplification. This segmentation allows each component to be optimized independently, with the multi-stage amplifier specifically designed to boost signals before they are affected by parasitic capacitance noise, thereby improving signal-to-noise ratio without excessive overall complexity
Solution Approach 2:
The storage capacitor is connected to the light-sensing element to preliminarily store the generated photocharges before they are read out. This preliminary storage action allows the signal to be accumulated and stabilized before amplification, reducing the impact of subsequent noise from parasitic capacitors and improving the overall signal-to-noise ratio
2Illumination intensity
If separate light sources are used for image sensing, then external illumination is provided, but the device complexity increases and noise is introduced
Solution Approach 1:
The display device's display pixels serve a dual function: they display images and simultaneously act as light sources for the image sensor. When the image sensor needs to capture images, the display pixels can be controlled to emit light, providing the necessary illumination without requiring separate dedicated light sources. This multi-functionality reduces device complexity and eliminates the noise that would be introduced by additional light source components
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 design effectively reduces noise and improves the signal-to-noise ratio, enabling high-sensitivity image sensing with reduced noise interference and eliminating the need for external light sources, thus enhancing image quality and sensitivity in display devices.
Implementation Method 1
a light-sensing element coupled between the first node and a second power source, where the light-sensing element generates photocharges in response to incident light
Data Source
AI summary
An image sensor includes a sensor pixel. The sensor pixel includes a first transistor coupled between a first power source and a first node, where the first transistor is turned on in response to a first control signal, a light-sensing element coupled between the first node and a second power source, where the light-sensing element generates photocharges in response to incident light, a storage capacitor coupled in parallel to the light-sensing element between the first node and the second power source, and an amplifier including a plurality of transistors coupled in series between the first power source and an output line, where the amplifier outputs a sensing signal corresponding to a voltage of the first node in response to a first driving signal.