Analysis of the difference between internal structure and principle of CMOS and CCD


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Regardless of any product, the quality depends mainly on the performance of the product, and the key to the performance has a great relationship with the product structure and working principle, as well as CCD and CMOS.

basic component

The CCD is developed on the basis of MOS transistors, and its basic structure is a MOS (metal-oxide-semiconductor) capacitor structure. It is formed on the surface of a semiconductor P-type silicon (Si) substrate by oxidation to form a layer of SiO2 having a thickness of about 1000?~1500?, and then depositing a layer of metal (such as aluminum) on the surface of the SiO2. Adding a bias voltage (called the gate voltage) to the metal electrode constitutes a MOS capacitor. Therefore, the CCD is constituted by a MOS capacitor array in which a row and a row are closely arranged on a silicon substrate.

The most basic CMOS image sensor is a P-type silicon wafer with a low impurity concentration as a substrate, and two highly doped N+-type regions are formed on the surface by diffusion as electrodes, that is, the source of the FET. And a drain, which is covered with a layer of silicon dioxide (SiO2) insulating layer by high temperature oxidation on the surface of the silicon, and a metal aluminum is deposited as a field above the insulating layer between the source and the drain. The gate of the effect tube. Finally, a photodiode is placed over the metal aluminum, which constitutes the most basic CMOS image sensor.

In addition, in the CMOS image pickup device, the electric signal is directly read from the CMOS transistor switch array, unlike the CCD, which requires line-by-line reading.

Internal structure

The CCD imager needs to be supplemented by more peripheral driving circuits to work. It can only output analog electrical signals, which are processed by subsequent address decoders, analog-to-digital converters, image signal processors, etc. The degree of integration itself is relatively low. If there are CCD digital cameras, there are often six chips, some as many as eight, and at least three, so that the camera volume can not be reduced, and the production cost is also high.

The CMOS imager does not require an additional peripheral processing circuit. It integrates a photodiode, an image signal amplifier, a signal reading circuit, an analog-to-digital converter, an image signal processor, and a controller onto a single chip, and is fabricated and processed. Just like the process of producing integrated circuits by semiconductor manufacturers. If you make a digital camera, you can integrate all the components of the digital camera on one chip, which is a "single chip camera." Therefore, the photoelectric image system using the CMOS chip can not only reduce the overall cost of the system and the time required for assembly, but also greatly reduce the size of the system and reduce the complexity.

working principle

In addition, the CCD is a semiconductor imaging device. The charge information stored by the CCD charge coupler needs to be read one bit after the synchronization signal control. The charge information transfer and read output need to have a clock control circuit and three The combination of different power supplies makes the entire circuit more complicated. Therefore, the CCD processing information is relatively slow, and its power consumption is relatively large; while the CMOS photoelectric sensor can take out the electrical signal after photoelectric conversion, the reading is relatively simple, and the image information of each pixel unit can be processed simultaneously. The CMOS photoelectric sensor only needs to work in a single group of power sources, and the power consumption is small, which can achieve energy saving.

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