Imaging principles and other differences between CCD and CMOS cameras

The second layer of CCD is the color separation filter. Currently, there are two color separation methods: the RGB primary color separation method and the CMYG complementary color separation method. These two methods have their own advantages and disadvantages. However, in terms of output, primary colors and complementary colorsCCDThe ratio is about 2: 1. Primary Color CCD has the advantage of sharp image quality and true color, but its disadvantage is noise. Therefore, the DC using primary color CCD generally does not exceed 400 in ISO sensitivity. Compared with the complementary CCD, a Y-yellow filter is added, which is more careful in color resolution, but sacrifices someResolutionIn the ISO value, complementary CCD can tolerate a high degree of sensitivity, generally can be set to more than 800. (For details about the two color separation methods, refer)

 

 

 

 

The third layer of CCD is the photosensitive flat, which is mainly responsible for converting the light source penetrating the color filter layer into an electronic signal and transmitting the signalImagesProcess the chip and restore the image.

Finally, let's talk about CMOS:

CMOS (Complementary Metal-oxide semiconductor) is a complementary metal oxide semiconductor, which is a semiconductor in microprocessor, flash memory, and specific purpose integrated circuits (ASIC ).TechnologyIs absolutely important. Both CMOS and CCD are semiconductors that can be used to feel light changes. CMOS is a semiconductor made of silicon and GE. It is achieved through a transistor with negative power and positive power on CMOS.Function. The current produced by these two complementary effects can be recorded and decoded by the processing chip.

The CMOS structure is relatively simple, which is the same as the existing large-scale IC production process, thus reducing the production cost.. In principle, the CMOS signal is a point-based charge signal, while the CCD is a current signal in the unit of behavior. The former is more sensitive, faster, and more energy-saving.Currently, advanced CMOS is not inferior to CCD, but the current development of CMOS technology is not mature.ApplicationAt the Professional levelDigitalOn cameras, many low-end digital cameras use low-end CMOS, and their imaging quality is poor.. The biggest drawback is that it is too prone to noise, mainly because of the earlyDesignSo that CMOS will cause overheating due to frequent changes in current when processing fast-changing images. Therefore, if you want to purchase a consumer-level digital camera, you still need to choose CCD as the image sensor. However, high-end SLR cameras are still dominated by CMOS.

Comparison of advantages and disadvantages

CCD CMOS
Design a single optical sensor connection Amplifier
The high-sensitivity opening is small and the sensitivity is low in the same area.
High Cost line quality impact, high cost CMOS integration, Low Cost
Low Resolution connection complexity, high resolution, and High Technology
Noise Ratio: single amplification; Low Noise: 1 million; high noise
Power consumption is directly amplified with high power consumption and low power consumption.

Due to the basic differences in construction, we can list the performance differences between the two. CCD is designed to ensure that the signal is not distorted during transmission (the exclusive Channel is designed), and the data integrity can be maintained by aggregating each pixel to a single amplifier; the CMOS process is relatively simple and there is no exclusive Channel Design. Therefore, you must first zoom in and then integrate the data of each pixel.

In general, the applications of CCD and CMOS are reflected in the imaging effect, which includes ISO sensitivity, manufacturing cost, resolution, noise and power consumption. Different types of differences:

ISO sensitivity difference: Since each CMOS pixel contains an amplifier and A/D conversion circuit, excessive additional devices compress the surface area of A single pixel's photosensitive area, so under the same pixel, in the same size, the sensitivity of CMOS is lower than that of CCD.

Cost Difference: CMOS is applicable to MOS processes commonly used in the semiconductor industry. All peripheral facilities can be integrated in a single chip at a time to save the cost and yield loss required for wafer processing; in contrast, CCD outputs information by means of Charge Transfer, and must establish another transmission channel. If a pixel fault (Fail) exists in the channel, it will lead to congestion of a whole line of signals and cannot be transmitted, therefore, the yield of CCD is lower than that of CMOS, and the manufacturing cost of CCD is higher than that of CMOS in addition to the peripheral areas such as the transmission channel and ADCs.

Resolution difference: in the first "sensitivity difference", because the structure of each CMOS pixel is more complex than that of CCD, its photosensitive opening is less big than that of CCD, compared with CCD and CMOS Sensors of the same size, the resolution of CCD sensors is usually better than that of CMOS. However, if the size limit is exceeded, the original CMOS photosensitive device in the industry can now reach 14 million pixels/full width, the advantage of CMOS technology in terms of the volume rate can overcome the difficulties in manufacturing large-sized photosensitive originals, especially the size of the full-width 24mm-by- 36mm.

Noise difference: because each CMOS sensor is paired with an ADC amplifier, if measured in millions of pixels, more than one million ADC amplifiers are needed, although they are products under unified manufacturing, however, each amplifier is more or less slightly different, and it is difficult to achieve the effect of amplification and synchronization. Compared with CCD of a single amplifier, CMOS will eventually calculate more noise.

Power Consumption difference: the charge driving mode of CMOS images is active, and the electric charge produced by the photosensitive diode is directly amplified by the crystal next to it, but the CCD is passive, the extra voltage is required to move the charge in each pixel to the transmission channel. This additional voltage usually requires a level above 12 volts (V). Therefore, CCD must have more precise power supply line design and withstand voltage strength, high driving voltage makes the power of CCD much higher than that of CMOS.

Source 1: differences between CCD and CMOS cameras

Source 2: imaging principles of CCD/CMOS-Introduction of Color Separation Filters and CMOS