What is image sensor (CCD and CMOS)?
By Steve Lowry 2018-06-14 7481 0
CCD (Charge Coupled Device)
CCD: as an integrated circuit, there are many capacitors neatly arranged can sense the light and convert the image into digital signal. Each small capacitor can transfer its electric charge to its adjacent capacitor by the control of external circuit. CCD is widely used in digital photography, astronomy, especially optical telemetry, optical and spectrum telescopes, and high-speed photography.
The electrical charge data for each pixel in each row of the CCD sensor can sequentially transfer to next pixel that output from the bottom and then amplified by an amplifier at the edge of the sensor.
Advantages of CCD image sensor
High Resolution: The image dot is μm class that can detect and recognize the fine object and improve the image quality. From 1 inch, 1/2 inch, 2/3 inch, 1/4 inch presented to 1/9 inch, the number of pixels from more than 100 thousand to 4-5 million.
Low Noise: CCD has low readout noise and dark current noises, thus improving the signal to noise ration (SNR), while with a high sensitivity so that the very low luminous incident light can be detected and its signal will not be blanketed that lead to the application of CCD will not be confined to the weather.
High Dynamic Range: To detect and distinguish between strong light and weak light at the same time, improve the system environment for range of application, the signal contrast phenomenon will not occur due to high variation in brightness.
Favorable Linearity: Between the intensity of the incident light source and the output signal is proportional to the relationship, the object information will not be lost, to reduce the signal for the processing costs compensation.
High Quantum Efficiency: Very weak incident light can be recorded, even though the distant sceneries in the dark night can be detected if the image enhancement tube and emitter accompanied.
Large Field of View: The large-area CCD can be manufactured by using semiconductor technology. The CCD that is equivalent to the conventional film has already been used in digital cameras, being the key elements to take over professional optical cameras.
Broad Spectral Response: can detect a wide range of wavelength light, increase the system flexibility and expand the application field for system.
Low Image Distortion: The distortion situation in image process will not occur and the original object information can be reflected faithfully by the usage of CCD sensor.
Small volume and light weight: CCD has the characteristics of small volume and light weight, therefore, can be easily installed in the artificial satellite and various navigation systems.
Low power consumption: not affected by the electromagnetic field.
The charge transfer efficiency is good: The efficiency coefficient affects the SNR and resolution rate, if the charge transfer efficiency is poor that will blear the image.
It can be mass-produced with the characteristics of stable quality, stand-up, difficult to aging, easy to use and maintenance.
CMOS (Complementary Metal-Oxide-Semiconductor)
CMOS is one of two major types of image sensor technologies used in digital cameras (the other being CCD). The image sensor of a digital camera serves as a digital substitute for film in ordinary cameras.
The camera sensor captures light, converts it to electric charge and processes it into electronic signals.
In the CMOS sensor, each pixel is adjacent to an amplifier and A/D conversion circuit, and output the data in a similar memory circuit way.
Advantages of CMOS image sensor
● Wide allowable power supply and voltage range, convenient to design power supply circuit.
● Large logic swing, high noise immunity.
● Low static power consumption: in the case of the same pixels, it has lower prices, and high cost performance, so it can develop towards the higher pixel and higher resolution.
● The gate-to-gate configuration maximizes the input resistance during CMOS, making the ability to drive similar logic gates much stronger than other series during CMOS operation.
Compared with CCD, CMOS is smaller in size, less 1/10 of the power consumption than that of CCD, and the price is also cheaper than CCD.
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