CCD type and its principle

The CCD was first invented by Bell Labs and has been in the history of the year for more than 33 years. Although the semiconductor process has made considerable progress, but the CCD is only a few manufacturers can produce, they are sony;philps;kodak;matsushita;fuji and sharp, Japanese manufacturers accounted for the overwhelming majority. In addition to the Fuji Super CCD uses a diamond (honeycomb) arrangement (this refers to the arrangement of each photosensitive diode), the other CCD are arranged in a rectangular way. Although they are arranged differently, they work based on the following four basic CCD types linear, interline, Full-frame, and Frame-transfer. CCD is more expensive, and the price is relatively stable, compared to cmos,cmos (common camera) prices have been declining.

The structure of the CCD is shown below:

Linear CCD

Called a linear CCD, it has a single line of pixels, and all the pixels are on one line. If you want to display a pair of images, the linear CCD needs to be scanned from the object surface. The image is made up of a row of lines, and obviously it is very slow to capture the scene. And it needs to use a stepper motor, which increases the complexity of the system, if the mechanical accuracy is not calibrated to affect the imaging, and mechanical motion will also bring a lot of noise, the current linear CCD on the flatbed scanner to use the most.

Interline, Full-frame, and Frame-transfer are designed as a queue-shaped CCD that uses multiple lines to form a rectangle or a square.

Interline CCD

Each pixel in the interline CCD has an area where the charge is stored, as if it were pumped, one line for photoelectric coupling and the other for storing the charge. These pixel storage areas are connected to a vertical charge transfer channel, up to the horizontal displacement register (shift register) at the top of the queue. This type of CCD has the widest range of applications, mainly because of their faster speed. The interline is designed to allow a pixel-stored charge to quickly shift to its adjacent storage area, where the charge is shifted to the horizontal shift register at the top of the row. It quickly removes storage charges from the storage area and prepares for receiving the next exposure. In digital cameras, this staggered-design CCD captures pixels fast enough and allows for continuous shooting, even for dynamic video capture. Most digital cameras on the market now use this CCD opto-coupler. The Interline CCD has an electronic shutter and progressive scan progressive scanning mode for high speed photography.

2, Interline CCD is also called interlaced transfer CCD, this CCD exposure generated by the charge is transferred to the attachment shift register, through the vertical transfer downward to the bottom, according to a certain sort of output. The advantage of this CCD is that the charge can be stored in the register after exposure, the continued exposure speed is faster, the photosensitive and transmission is not in the same column, thus avoiding the trailing phenomenon. The disadvantage is that the register occupies the photosensitive surface area, but also the corresponding sacrifice of the dynamic range, each pixel of the chip is not all photosensitive, for positioning measurement requirements of higher applications will have an impact.

Full-frame CCD

All the pixels are used for photosensitive, the effective photosensitive area increases. However, the sensitivity and charge output process should be separated, so the speed is not too high. Its photosensitive unit is also its charge register, it is composed of CCD photosensitive unit, Parallel CCD displacement Register, parallel displacement register clock Controller, serial CCD displacement register and serial Displacement register clock controller and output signal amplifier.

The CCD uses all the pixels in the photosensitive region, so when there is a charge transfer, these pixels are used to process the charge transfer and cannot continue to capture the new image. In the process of pixel transmission, if the sensor receives the light again, it will affect the image and represent the light spot on the image. Due to the inability to electronically limit the occurrence of this kind of image, the general digital camera will be mechanically closed shutter way to isolate the lens injection of light. Digital cameras with Full-frame CCD are the only type of mechanical shutter that must be installed, and the CCD's photosensitive mode limits its continuous shooting function. The Full-frame CCD is typically used on top-level digital cameras to obtain high image density (details), such as digital backs and mid-range images.

1,full frame CCD is also called Pang CCD, each pixel of the array is photosensitive. When transmitting, each column is transferred to the corresponding position on the single-line serial register. At the same time the serial register is transferred to the output of the CCD array. Full frame can be used throughout the photosensitive area, effectively increase the photosensitive area, but also adapt to the long exposure. Therefore, in the last frame after exposure, the charge output, otherwise, the next frame exposure begins, the previous frame is still in the readout stage, it is easy to appear trailing phenomenon. The CCD must therefore use a mechanical shutter. It also limits the ability of the full frame CCD to take pictures continuously.

Frame-transfer CCD

Frame-transfer CCD architecture is very special, we see its upper part is a photoelectric coupling device, the lower half is composed of horizontal CCD storage queue, which consists of horizontal pixel queue clock controller, horizontal storage queue clock controller. The serial CCD displacement Register and the serial Displacement Register clock controller and the signal output amplifier are composed.

The Frame-transfer CCD is very similar to the Full-frame CCD, but it masks the temporary storage area used for the charge by a half-group of queues, calling it "storage array" to be appropriate, when a photosensitive pixel obtains their charge, It will quickly transfer the charge to the storage queue. This operation does not have a shutter delay, they are very fast capture devices. However, the concurrent charge transmission period and the light-sensitive period still cause the "stain" of the image, and the interline CCD improves the design, allowing for simultaneous charge transfer while shooting, which is a small difference between them.

Philips ' Frame-transfer CCD (face scan) technology is known as the true frame sensor structure (which was developed by Philips and is currently being used by Sanyo, Sanyo's vpc-sx550 is a typical example, It can reach a shooting speed of 30 frames per call, and its storage area on the sensor is protected by a metal layer to prevent light from entering. We know that typical interline CCD shooting rate is 5-10 per second, and Philips claims that their frame Transfer CCD can reach a rate of 30-60 frames per second. This is the speed of the real video signal.

With only a handful of CCD manufacturers, many of them industry giants, the competition between them is extremely fierce. Some small differences between the sensors also attract different buyers, so these CCD manufacturers are improving the basic CCD architecture to improve their competitiveness. Fuji's Super CCD is the only CCD with a honeycomb structure, and the eight-edged shape is used to maximize the effective area of the CCD (we know that the structure of the honeycomb is a very efficient geometric shape, and the space utilization is the most highly utilized geometry in nature). This allows for maximum density per pixel on the CCD, and the shape of the pixel allows it to have a larger photosensitive area for better dynamic range. Fuji claims that the technology has a better signal-to-noise ratio and dynamic range, and we tested the consumer digital camera Fujifilm 4700 using the first generation Super CCD, but we were disappointed with its image quality. But the next generation of Fuji digital cameras has optimized the Super CCD technology, and we've found that its images are sharper than competing cameras (although the translator believes that Super CCD images are known for their softness), their image quality is quite good, and the test camera is Fujifilm FinePix S1 Pro, no wonder image quality is good, this is a positioning professional market SLR digital camera.

The industry has developed different types of ccd:line (Linetype), interline (scanning), Full-frame (Panorama) and Frame-transfer (Quan Zhuan) due to different types of job requirements.

Linear CCD is a one-dimensional photosensitive point composition, through the stepper motor scanning image, because the photo is a row of lines, so the speed of the two-dimensional digital camera comes slow, the CCD is mostly used in the platform scanner.

Scanning type of CCD exposure generated by the charge is transferred to a nearby shift register, by vertical transfer downward to the bottom, according to a certain sort of output, its advantage is that after exposure can be stored in registers, continue to take pictures faster, the disadvantage is that registers occupy the area of the photosensitive surface, the corresponding sacrifice of the dynamic range, The CCD is low cost and is used in monitors, camera phones, or low-end digital cameras.

Panorama CCD is a more simple structure of the photosensitive design, in view of the shortcomings of the scanning type, the panorama can take advantage of the entire photosensitive area (no storage area design), effectively increase the photosensitive area, but also adapt to long exposure, the exposure process and the same line, but the photosensitive and charge output process is separate. As a result, the digital camera of the panoramic CCD must use a mechanical shutter (no electronic shutter) when transmitting the charge, and also limit the ability of the panoramic CCD to take pictures continuously. The panorama type is mostly used on professional-grade cameras.

The architecture of the Quan Zhuan CCD is between scanning and panorama, sometimes called a full scan, which is divided into the upper and lower parts, the upper part is the photosensitive area and the lower part is the temporary storage area. Overall, the Quan Zhuan CCD is very similar to a panoramic CCD, which is characterized by direct planning of a large storage area. Once the Quan Zhuan CCD is working, it can quickly transfer the charge to the lower storage area, which itself can continue to be exposed to the camera. This design allows Quan Zhuan to use the electronic shutter as well as scanning, while also increasing the photosensitive area and speed, taking into account both dynamic and static shooting capabilities. Most digital cameras use this type of CCD.

CCD type and its principle