Detailed HD monitoring: CCD and CMOS analysis and comparison

I. Definition of Terms and Working Principles CCD:

English full name: Charge-coupledDevice, Chinese full name: charge-coupled components. It can be called a CCD image sensor. CCD is a semiconductor device that can convert optical images into digital signals. It is made using a high-sensitivity semiconductor material and contains a number of photosensitive elements. Each photosensitive element is called a pixel. The CCD can be seen as an aggregation of these pixels. The more pixels a CCD contains, the higher the screen resolution it provides. The CCD acts like a film, but it converts image pixels into digital signals. When the CCD surface is exposed to light, each photosensitive unit will reflect the charge on the component, and all the signals generated by the photosensitive units add together to form a complete picture.

CMOS:

The full name in English is ComplementaryMetalOxide Semiconductor, or Complementary Metal Oxide Semiconductor, which is a semiconductor that records light changes like the CCD. The manufacturing technology of CMOS is no different from that of a general computer chip. It mainly uses a semiconductor made of silicon and germanium to make a negative-electrode (N-pole) and positive-electrode (P-pole) semiconductor coexist in the CMOS. The current generated by the two complementary effects can be recorded and interpreted by the processing chip as an image. Then, the analog video signal obtained by the on-chip analog-to-digital converter (ADC) is converted into a digital signal output.

Second, CCD and CMOS contrast 1, pixel structure is different
The first difference between CCD and CMOS is reflected in the difference in the photoreceptor unit or pixel structure. The former photosensitive element includes a memory cell for controlling adjacent charges in addition to the photosensitive diode, and the photosensitive diode occupies most of the area. The composition of the CMOS sensor is more complicated. Besides the photodiode at the core, it also includes an amplifier and an analog-to-digital conversion circuit. Each pixel is composed of a photodiode and three transistors. The photodiode occupies only A small part of the entire component.

Compared to CMOS sensors, the effective light-sensing area of ​​the CCD sensor is large. Under the same conditions, strong light signals can be received, and the corresponding output electrical signals are also stronger. The result is the image captured by the CMOS sensor. The content is not as rich as the CCD sensor, the sharpness is poor, the loss of image details is serious and the noise is significant, which is why the early CMOS sensors were mostly used in low-end applications.

2, ADC location and number are different

The second difference between CCD and CMOS is reflected in the difference in the position and number of ADCs (analog-to-digital converters). Each pixel of the CCD corresponds to only one ADC. Each time the light sensor is exposed, pixel shift processing is performed after the shutter is closed. The control circuit transmits the data to the “buffer” in a serial manner and is output from the bottom line. The amplifier next to the CCD is amplified and the ADC output is connected in series. In contrast, an ADC is connected next to each pixel in the CMOS design. The signal is directly amplified and converted into a digital signal.

It is because of this difference that the signals of each photosensitive element in the CCD sensor can form a unified output. After the output data is uniformly processed by the amplifier, the electrical signal intensity of each image point is increased by the same magnitude; and CMOS Each photosensitive element carries an ADC, and it cannot be guaranteed that the magnification of each image point is strictly identical, so that the magnified image data cannot represent the original appearance of the photographed object. Reflected in the final output, noise is inevitable in the image, and the image quality is lower than that of a CCD sensor.

3, specific parameter comparison



Comparison of specific parameters of CCD and CMOS

Third, both applications

Through the above comparative analysis, we can see that CCD and CMOS have their own advantages. Based on this, we can do our best to avoid weaknesses and choose a CCD or CMOS camera in different applications.

1. CCD camera should be used in low illumination environment

Due to the large effective area of ​​the CCD light-sensing unit, the original appearance of the object can be relatively clearly displayed in a low-light environment. In low-light environments, such as dimly lit parking lots, stairwells, enclosed passages, and darkrooms, sensitive CCD cameras should be used. ,

2. Using CMOS Cameras in Covert Environments

CMOS sensors can be made very small, so CMOS cameras can be made very small. The CCD camera is limited to the influence of the external complex circuit, and the volume cannot be miniaturized as CMOS. For cameras where roads, gates, and other cameras are vulnerable to attack by criminals, the use of CMOS cameras can achieve covert enforcement and avoid attacks.

3, CCD camera is used for occasions with high image quality requirements

Because there is only one ADC in each row in the CCD structure, the signal amplification ratio is the same, so the image restoration is real and natural, the noise is low, and the CCD camera should be selected in the occasion where the image quality is demanding. The higher the pixel size, the larger the CCD has better image quality. Current monitoring CCD cameras have been able to achieve 2 million to 5 million high pixels. , 4, High-frame camera use CMOS camera better CMOS sensor can directly convert the photoelectric signal generated by the image semiconductor into a digital signal, processing speed is very fast. This advantage makes the CMOS sensor very useful for high-frame cameras with speeds of 400 to 2000 fps. So for high-speed camera sites, the use of CMOS cameras is better.

Fourth, the development trend

CCD and CMOS are basically invented at the same time, but due to CMOS technology problems, CMOS noise and other parameters are far inferior to CCD, so CCD has developed rapidly in the past few decades. However, with the improvement of CMOS technology, CIS (CMOS Image Sensor) is getting better and better, and it has a great potential to replace CCD. Because the CIS that solves the technical problem has lower cost, it is more suitable for mass production.

In view of this, Shenzhen Shiguo's explosion-proof camera movement mainly chooses the CCD sensor. The world's explosion-proof HD network camera selects the CMOS sensor, because the mega-camera selection CMOS sensor is more appropriate in terms of cost performance and performance.

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