Review of In-Pixel Gain Amplifiers and Readout Circuits for Low-Light CMOS Image Sensors

Area of Science:

• * Electrical Engineering
• * Materials Science
• * Optics

Background:

• * Low-light performance of image sensors is critical for various applications.
• * Enhancing signal paths from photon conversion to chip outputs is key.
• * High-gain in-pixel amplifiers, column amplifiers, and reduced capacitance are methods, but face challenges.

Purpose of the Study:

• * To review in-pixel gain amplifiers and signal chain electronics in high-conversion-gain CMOS image sensors over the last two decades.
• * To classify in-pixel gain amplifiers based on amplification techniques.
• * To analyze column-referred conversion gain and noise for different topologies.

Main Methods:

• * Classification of in-pixel gain amplifiers by amplification technique.
• * Analysis of column-referred conversion gain and noise for each topology.
• * Comparison of performance metrics for various in-pixel gain amplifiers.

Main Results:

• * A framework is provided to highlight the best achieved input-referred noise in CMOS image sensors over the past 15 years.
• * Tradeoffs between conversion gain, pixel full-well capacity, and input read noise are examined.
• * Various in-pixel gain amplifier topologies are analyzed for their effectiveness in low-light conditions.

Conclusions:

• * In-pixel gain amplifiers are crucial for enhancing low-light performance in CMOS image sensors.
• * Understanding tradeoffs is essential for optimizing sensor design for specific low-light applications.
• * Continued research into amplifier design can further improve image sensor capabilities.