The Difference between CCD and CMOS

1970 is a landmark year for image processing industry; the United States Bell Labs invented the CCD. After 20 years, people use it to create the digital cameras; image-processing industries are pushed into a new field. Digital camera without film and rinse, can repeat shooting and immediate adjustment; Imaging can be copied without limit and not reduced quality, facilitate the permanent preservation and can be used for electronic transmission and processing. Its birth to the image processing industry has brought a revolution.

Later, it was discovered that a kind of processing chip in the computer system can be used as digital camera sensitive sensors or CMOS, featuring mass production and low-cost that is businessmen pursuit. Industry analysis believes that it in the near future may replace CCD, but now they still coexist. Many people believe that: "Intelligent sensors, particularly CCD, are the extremely core components, is the heart of digital cameras. "This is not true: Intelligent sensor, or CCD, its function is to capture light and converted them to electronic signals through lens, CCD is not so much the heart, as it is eyes for the cameras. In researching cameras, the CCD or CMOS sensor photosensitive though is a very important component, determine a large extent the pixel camera, However, CCD / CMOS chip do not take the dominant position of the cost, the more sophisticated areas, the more prominent this character.

From a view of technical point, CCD and CMOS have four different aspects:

1. Data readout method

The charge stored by CCD charge-coupled device, need the control of synchronous signal to read after being translated. Charge transfer and information read and output need work with clock control circuit and three different power resources. The whole circuit is much more complex. CMOS photoelectric sensors directly generated electronic signal after conversion, the signal is very simple to read.

2. Speed

CCD charge-coupled device output the information under the control of clock control circuit; the speed of output is slow. While the CMOS can capture the signal and output it at the same time, process the image data of each unit in the meanwhile. Of course, the speed is faster than CCD’s.

3. Power source and electricity consumption

CCD needs three power sources to support its work; the consumption of electricity is serious. CMOS only need one power source and the consumption is small, maybe equivalent to 1/8 to 1/10 of CCD. Therefore, CMOS has a real advantage in saving energy.

4. Image quality

Because CCD is begin made in early days, its technology is maturity, and adopt PN or SiO2 to reduce the noise, so the image quality is better than CMOS. But in recent years, with the development of the noise eliminating technology, CMOS will get much better image quality.

Besides, the internal and external structures of them are different.

1. The internal structure (itself structure)

The each image point of CCD consists of one Photodiodes and one charge storage zoon next to charge storage and under its control. Photodiodes convert the photons into electron and the relationship between the numbers of electron and intensity of light is direct ratio, when read these charge, the data moved into the ISA Server. The image generated from this structure has the merits of low noise and high function, but need clock signal and Technology for Deflective Pressure to produce CCD, so that the whole system is complex, increase the consumption of electricity and cost.

Amos’s electronic components can be integrated at the one process period, such as Digital Logic Circuit, Clock Driver and the ADC. It likes storage and each image point includes one Photodiodes, one charge or voltages convert unit, one reset and others. It can read the signal by simple X-Y addressing technology.

2.External structure (the application of the products)

CMOS can combine all of components of digital camera into one chip, including photosensitive element, picture amplifier, signal readout circuit, image signal processor and controller and among others. Only one chip can carry out many functions, so the whole cost of it is low.