Introduction to Camera Module" of Hardware Circuit Design
October 31, 2022
Introduction to Camera Module" of Hardware Circuit Design
The composition of the camera module
We all know that there are various forms of cameras or external interfaces, but the internal modules are basically composed of lenses, bases, filters, sensors, DSP (including ISP), PCB substrates, etc. As for the external interfaces According to different application scenarios of the product, there are various interface types. The same is true for the DSP part. According to different application scenarios, different usage methods, and different processing requirements, some are directly included in the sensor, and some are directly included in the sensor. An external dedicated chip is required for processing.
Lens & Holder
The lens is a device that images the scene on the sensor, and it usually consists of several lenses. From the material point of view, the camera lens can be divided into plastic lens and glass lens.
Usually the lens structure of the camera is: 1P, 2P, 1G1P, 1G2P, 2G2P, 4G (P stands for Plastic, G stands for Glass) and so on. The more lenses, the higher the cost; glass lenses are more expensive than plastic. Therefore, a good-quality camera should use a glass lens, and the imaging effect will be better than that of a plastic lens. In order to reduce costs, most camera products on the market generally use plastic lenses or semi-plastic and semi-glass lenses (ie: 1P, 2P, 1G1P, 1G2P, etc.).
In terms of material, the lens mount is divided into metal material and plastic material. If the lens holder is distinguished from the interface, it can be divided into C, CS, M12, M9, M8 and other lenses with different interfaces, which is to choose according to your needs.
The origin of the word "C" is the initials of "cinema" (movie), and the origin of the C-mount is the camera lens. Currently, C-mount is the standard interface from 16mm video cameras, TV cameras, and trinocular microscopes. C-mount lenses provide a male thread to mate with the camera's female port. The diameter of the threads is 1 inch (25 mm), with 32 threads per inch, and is designed according to the "ANSI B1.1" standard.
The focal plane distance of the C-mount is 17.526 mm.
The CS interface is 12.52 mm focal plane distance, and the rest of the parameters are the same as the C interface (C-Mount Adapter).
So using a "C/CS 5mm adapter" can convert the "C mount lens" into a "CS mount".
Image Sensor
Image sensors are divided into two categories: CCD (Charge Couple Device): Charge Coupled Device CMOS (Complementary Metal Oxide Semiconductor): Complementary Metal Oxide Semiconductor. The advantages of CCD are high sensitivity, low noise and high signal-to-noise ratio. However, the production process is complicated, the cost is high, and the power consumption is high. The advantages of CMOS are high integration, low power consumption (less than 1/3 of CCD), and low cost. However, the noise is relatively large, the sensitivity is low, and the light source requirements are high.
There are three main packaging processes for Image Sensor: LCC (Leadless Chip Carrier), CSP (Chip Scale Package), and COB (Chip On Board).
There are two common external interfaces of Image Sensor: serial and parallel. The serial basically adopts CSI, and the parallel adopts DVP.
ISP is the abbreviation of Image Signal Processor, and DSP is the abbreviation of Digital Signal Processor.
ISP is generally used to process the output data of Image Sensor (image sensor), such as AEC (automatic exposure control), AGC (automatic gain control), AWB (automatic white balance), color correction, Lens Shading, Gamma correction, removal of dead pixels , Auto Black Level, Auto White Level and other functions.
The DSP has more functions, it can do some photography and echo (JPEG codec), video and playback (Video codec), H.264 codec, and many other processing. Personally understand that ISP is a special kind of DSP that processes image signals. At present, the ISP can exist alone as a chip, or it can be directly integrated in the Image Sensor. The external output is the YUV image processed by the ISP. If the Image Sensor without ISP outputs the image data in RAW format. It can also be directly integrated in the AP, and the ISP inside the AP can be directly used for image signal processing.