Basic Introduction CMOS is the abbreviation of **Complementary Metal Oxide Semiconductor**. It refers to a technology for manufacturing large-scale integrated circuit chips, or chips fabricated with this technology, serving as a readable and writable RAM chip on computer motherboards. Owing to its read-write capability, it is applied on motherboards to store data after BIOS configures computer hardware parameters, and this chip is exclusively used for data storage. Additional digital signal processing circuits can be integrated on CMOS image sensor chips, such as AD converters, automatic exposure control, non-uniformity compensation, white balance processing, black level control, gamma correction, etc. To enable rapid computation, DSP devices with programmable functions can even be integrated with CMOS components, forming single-chip digital cameras and image processing systems.

Overall Architecture of Image Sensors A CMOS image sensor is essentially a chip, mainly consisting of modules such as a photodetector array (Bayer array, also known as pixel array), timing control, analog signal processing, and analog-to-digital conversion. The functions of each module are as follows: 1. Pixel Array: Performs photoelectric conversion, converting photons into electrons. 2. Timing Control: Governs the readout and transmission of electrical signals. 3. Analog Signal Processing (ADC): Performs noise reduction on the signals. Among these, the pixel array occupies the largest area of the chip. It is composed of individual pixels, corresponding to each pixel in every image we see. Each pixel contains a photosensitive area and a readout circuit. After the signal of each pixel is processed by the analog signal processing module, it is sent to the ADC for analog-to-digital conversion before being output to the digital processing module.

Working Principle According to the functional block diagram of the CMOS image sensor, its working process can be divided into the following three main steps. Functional Block Diagram of the CMOS Image Sensor Step 1: External light irradiates the pixel array, triggering the photoelectric effect and generating corresponding electric charges within the pixel unit.

Working Principle The scene is focused onto the image sensor array through an imaging lens. The image sensor array is a two-dimensional pixel array, where each pixel contains a photodiode. The photodiode in each pixel converts the light intensity on the array surface into an electrical signal. Step 2: Select the target pixels via the row selection circuit and column selection circuit, and read out the electrical signals from the pixels. During the selection process, the row selection logic unit can scan the pixel array either line by line or in an interlaced manner, and the same applies to the column selection. The combination of row and column selection logic units enables the window extraction function of the image. Step 3: Perform signal processing on the corresponding pixel units. Image signals from row pixel units are transmitted through the signal bus of each column to the corresponding analog signal processing unit and A/D converter, where they are converted into digital image signals for output. The primary function of the analog signal processing unit is to amplify the signals and improve the signal-to-noise ratio. After amplification, the pixel electrical signals are sent to the Correlated Double Sampling (CDS) circuit for processing. Correlated Double Sampling is a crucial method for high-quality devices to eliminate certain interferences. Its basic principle is that the image sensor outputs two channels: one is the real-time signal and the other is the reference signal. Identical or correlated interference signals are removed through the differential comparison of the two signals. The signals are then sent to the Analog-to-Digital Converter to be converted into digital signals for output. In addition, to produce a practical camera with qualified image quality, the chip must integrate various control circuits, such as exposure time control and automatic gain control.

Application Scenarios Digital Cameras Under the control of the electronic shutter, the color CMOS camera captures an image and stores it in DRAM, before transferring it to flash ROM for preservation. CMOS can also implement numerous other functions, such as analog-to-digital conversion, on-board signal processing, white balance adjustment and camera control. At present, almost all entry-level digital cameras are equipped with CMOS image sensors.

Automotive Field Including Rear View Camera (RVC), Surround View System (SVS), Camera Monitoring System (CMS), FV/MV, DMS/IMS systems, etc.

Satellite Remote Sensing Currently, for nanosatellites weighing less than 10 kg, optical imaging technology (mainly visible light imaging) serves as the primary method for nanosatellites to perform Earth observation missions. In visible light systems, solid-state imaging devices such as CCDs are widely employed in their electro-optical systems for remote sensing imaging. Benefiting from its inherent advantages, CMOS imaging devices boast broad application prospects on micro-nanosatellites, including CMOS cameras, satellite sensors, MEMS micro gyroscopes, micro accelerometers, and other components.