What is a CCD sensor?
CCD (Charge-Coupled Device) is a sensor used in digital and machine vision cameras to capture stationary and moving objects, measured in megapixels. The megapixel count in digital camera specifications refers to the CCD's resolution. A CCD is a photosensitive semiconductor chip used to capture images and is widely used in scanners, copiers, and filmless cameras. Similar to film, light passes through a lens, projecting image information onto the CCD. However, unlike film, CCDs cannot record image data, nor can they permanently store it, and they don't even have "exposure" capabilities. All image data is continuously fed into an analog-to-digital converter, a signal processor, and a storage device (such as a memory chip or memory card). Before the introduction of CMOS image sensors, CCD sensors were widely used in industrial machine vision systems for quality inspection, monitoring, and control.
What is a CMOS imaging sensor?
CMOS (Complementary Metal-Oxide Semiconductor) is a technology that powers integrated circuits. It's a crucial chip in computer systems, storing vast amounts of data needed for system boot. CMOS image sensors and complementary metal-oxide field-effect transistors work by the photoelectric effect that occurs when light shines on a pixel array, generating electrical charges within the pixel units and ultimately converting them into a digital image output. CMOS technology powers many of today's electronic devices, including batteries, microprocessors, and digital and smartphone cameras. Unlike CCD sensors, CMOS sensors do not require specialized manufacturing techniques.
Due to their different structures, they each have their own strengths in terms of performance.
CMOS: Fast response, low power consumption, high noise, unevenness, image quality is greatly affected by noise, lower ISO.
CCD: Slow response, high power consumption, low noise, uniform image quality, high ISO.
Unlike newer CMOS sensors, CCD sensors require specialized manufacturing processes, which are typically more expensive. Therefore, CCD sensors generally offer very high quality and light sensitivity, enabling them to provide clear images with low noise.
CMOS sensors are inexpensive to manufacture using traditional manufacturing techniques employed by most microprocessors. They are also considered more energy efficient. According to Jacob Fraden’s “Handbook of Modern Sensors,” CCD sensors can consume up to 100 times the power of a CMOS image sensor.
1. Information Reading Method: The charge information stored in a CCD charge coupler needs to be transferred bit by bit under the control of a synchronization signal before it can be read. The charge information transfer and reading output require a clock control circuit and three different power supplies, making the entire circuit relatively complex. CMOS photoelectric sensors directly generate current (or voltage) signals after photoelectric conversion, making signal reading very simple.
2. Speed: CCD charge couplers need to output information bit by bit, line by line, under the control of a synchronous clock, which is relatively slow; while CMOS photoelectric sensors can extract electrical signals at the same time as acquiring light signals, and can also process the image information of each unit at the same time, making them much faster than CCD charge couplers.
3. Power supply and power consumption: Most CCD charge couplers require three power supplies, resulting in high power consumption; CMOS photoelectric sensors only require one power supply, consuming very little power, only 1/8 to 1/10 of that of CCD charge couplers. CMOS photoelectric sensors have a significant advantage in energy saving.
4. Imaging Quality: CCD charge-coupled device (CCD) fabrication technology started earlier and is mature. It uses PN junctions or silicon dioxide (SiO2) isolation layers to isolate noise, giving it a certain advantage in imaging quality compared to CMOS photoelectric sensors. Due to the high integration density of CMOS photoelectric sensors, the close proximity of various photoelectric sensing elements and circuits leads to significant optical, electrical, and magnetic interference, greatly impacting image quality and preventing CMOS photoelectric sensors from practical application for a long time. In recent years, however, the continuous development of CMOS circuit noise reduction technology has provided favorable conditions for producing high-density, high-quality CMOS image sensors.
