Charge-coupled device

A charge-coupled device (CCD) is an integrated circuit that helps us capture images and videos. It is made up of many tiny parts called capacitors that can move tiny bits of electric energy to each other. This makes it very useful for turning light into digital information.

In a CCD image sensor, each small area, called a pixel, can catch light and change it into electric charge. These pixels are made from special materials that let them do this very well. When light hits the sensor, it creates tiny charges that the CCD can read and turn into a picture.

CCDs were very important for making high-quality pictures in things like medical machines and science tools. They were also used in early digital cameras. But now, another kind of sensor called a CMOS sensor is used more often because it is cheaper and faster, even though CCDs were once the best.

History

The charge-coupled device (CCD) is based on a special kind of electronic structure called the metal–oxide–semiconductor (MOS). In the late 1960s, researchers Willard Boyle and George E. Smith discovered that tiny electric charges could be stored and moved along a row of these structures. They invented the CCD in 1969, and soon after, the first experiments showed that it could be used to capture images.

Over the next few years, scientists and companies worked to improve CCD technology. They created better cameras and sensors using these devices. By the 1980s, CCDs were being used in many consumer video cameras and still cameras, making digital imaging possible. In 2009, Boyle and Smith received a top science prize for their important discovery.

Basics of operation

In a charge-coupled device (CCD), light from a picture passes through a lens and lands on special parts called capacitors. These capacitors collect electric charge based on how bright the light is in each spot.

After the picture is captured, a special circuit moves the charge from one capacitor to the next, like a line of people passing a ball. Finally, the last capacitor sends its charge to a charge amplifier, which changes the charge into a voltage. This process turns the whole picture into a set of voltages that can be turned into a digital image or an analog signal for a camera.

Detailed physics of operation

A charge-coupled device (CCD) is a special chip that can capture images by using tiny parts called capacitors that are linked together. When light hits these parts, it creates tiny particles called electrons. These electrons move in a specific way to create an image.

CCDs are made from a material called silicon and are built in very clean and careful ways. They have special layers and patterns that help move the electrons from one place to another, making sure the image is clear and accurate. This technology is used in many cameras and other devices that need to take pictures.

Architecture

CCDs are special chips used in cameras and other devices to capture images. They come in different designs, each with its own benefits.

One common design is called "full-frame". In this type, the whole chip is used to capture the image, but it needs a mechanical shutter to prevent blurring.

Another design is "frame-transfer". Here, half of the chip is covered and used to store images. This allows quick moving of the image to the storage area, so a mechanical shutter isn’t always needed.

A third design is "interline", where every other column is used for storage. This lets the image move very quickly, almost instantly, with almost no blurring.

These different designs help decide which is best for a particular use. For example, cameras might choose one type, while telescopes might choose another, based on what works best for them.

CCDs are used in many devices like digital cameras, scanners, and video cameras. They can capture about 70 percent of the light that hits them, which is much better than old film cameras that only caught about 2 percent.

They also work well with infrared light, which is why some cameras can see in the dark or pick up signals from remote controls. To make them even better in low light, they can be cooled, which helps reduce unwanted noise and improves their sensitivity.

Use in astronomy

CCDs are very useful for astronomers because they can capture clear images of stars, planets, and other objects in space. Unlike old photographic plates, CCDs are easy to use and can turn light into electronic signals very well.

Astronomers take many pictures with CCDs to reduce unwanted changes in the images, such as random changes caused by heat or high-energy particles from space. Special steps help clean up these pictures so they show true details of space objects. Big telescopes like the Hubble Space Telescope use these steps to turn raw data into beautiful images.

When taking long pictures of faint objects like galaxies, special supports are needed to keep the telescope steady. Some CCD cameras use a second chip to watch for any movement and correct it automatically. One special way to use CCDs is called drift-scanning, where the camera moves in sync with the stars, allowing telescopes to capture larger areas of the sky. Famous projects like the Sloan Digital Sky Survey and the Gaia space telescope use this method. CCDs are also important in tools that break up light to study objects in space, such as spectrometers and interferometers.

Color cameras

See also: List of digital cameras with CCD sensors

Digital color cameras, like those in smartphones, use a special layer on top of their sensors called a color filter array. The most common pattern is the Bayer filter, named after the scientist who invented it. In this pattern, every group of four pixels includes one red, one blue, and two green pixels. This helps the camera capture details better because our eyes are more sensitive to green light.

Some cameras, especially professional ones, use three separate sensors to capture red, green, and blue colors more clearly. This can make the colors look more natural and detailed. For scientific work, like looking at very small things under a microscope, special methods can improve the clarity of colors even more.

Sensors for these cameras come in different sizes, often described using old terms like "1/2 inch" or "2/3 inch," which started back when cameras used different types of tubes.

Main article: Image sensor format

Blooming

When a camera uses a CCD for a long time, too much light in one spot can cause extra lines in the picture, called blooming. This happens because the part that stores the light's energy gets too full and spills over.

Some special designs in CCDs help stop this blooming. These designs use a small part of the camera sensor to safely move away the extra energy, so the picture stays clear.