CMOSsensor

A CMOS sensor, or complementary metal-oxide-semiconductor image sensor, is a type of image sensor used in digital cameras and other imaging devices. It integrates the photodiode array that captures light with the peripheral circuitry, including amplifiers, analog-to-digital converters, and often signal processing, on a single integrated circuit. CMOS sensors are manufactured using standard CMOS fabrication processes, enabling compact, cost-effective production and integration with readout electronics.

History and development: Early image sensors used CCDs. The active pixel sensor (APS) concept emerged in the 1990s as a CMOS alternative. A major milestone was the development of global shutter and on-chip processing, which improved performance for high-speed and high-dynamic-range imaging. Over the past two decades CMOS sensors have largely supplanted CCDs in consumer devices due to lower power consumption, higher integration, and cost advantages.

Operation: Each pixel contains a photodiode that converts incident photons to charge. Readout typically occurs by a rolling shutter or, in some sensors, a global shutter. Many CMOS sensors include on-chip amplification, correlated double sampling, and analog-to-digital conversion. Back-illuminated designs improve quantum efficiency by relocating metal interconnections to the back surface, increasing light capture.

Advantages and limitations: CMOS sensors offer low power, small size, high readout speeds, and easy integration of image processing. They historically faced challenges with fixed-pattern noise and lower image quality compared to early CCDs, but modern CMOS sensors achieve high dynamic range, low noise, and excellent color fidelity, making them suitable for smartphones, automotive cameras, and surveillance. Global shutter variants mitigate motion artifacts in high-speed imaging.

Variations and applications: Variants include stacked CMOS sensors, which separate imaging and processing layers, and back-side illuminated designs. Applications span consumer cameras, smartphones, video surveillance, automotive ADAS, industrial inspection, medical imaging, and scientific instrumentation.