[Camera]Camera module hardware

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Camera module, full name is CameraCompact Module, abbreviated as CCM. CCM contains four major components: lens, sensor, soft board (FPC), and image processing chip (DSP). The important components that determine the quality of a camera are: lens, image processing chip (DSP), and sensor. The key technologies of CCM are: optical design technology, aspheric mirror manufacturing technology, and optical coating technology.

Working principle: The light collected by the object through the lens is converted into an electrical signal through a CMOS or CCD integrated circuit, and then converted into a digital image signal for output through the internal image processor (ISP). It is processed by a digital signal processor (DSP) and converted into standard GRB, YUV and other format image signals.

? Lens is a device that can receive light signals and concentrate the light signals on the photosensitive device CMOS/CCD. Lens determines the lighting rate of the sensor, and its overall effect is compared to a convex lens.

? Generally, the lens structure of a camera is composed of several lenses, including plastic lens (PLASTIC) and glass lens (GLASS). The lens structures usually used by CAMERA are: 1P, 2P, 1G1P, 1G3P, 2G2P, 4G, 8P, etc. The more lenses, the higher the cost; glass lenses are more expensive than plastic lenses, but the imaging effect of glass lenses is better than that of plastic lenses. Currently, the cameras configured for mobile phones on the market are mainly 1G3P (composed of 1 glass lens and 3 plastic lenses) in order to reduce costs.

A. Eliminate as much Flare as possible

B. Image quality and clarity

C. CRA (Chief Ray Angle) must match and reduce shading (Lens cra < Sensor CRA, the difference is preferably within 2 degrees)

D. Make the aperture as large as possible

E. Distortion as slight as possible

(1) Focal length: The length of the focal length of the lens determines the size of the image taken, the size of the field of view, the size of the depth of field and the perspective strength of the picture. Generally speaking, for a single lens, it is the distance from the center of the lens to the focus, while a camera lens is composed of multiple lenses, which is much more complicated. The focal length here refers to the distance from the center point of the lens to the clear image formed on the photosensitive device (CCD).

(2) Field of view: We often use the horizontal field of view to reflect the shooting range of the picture. The larger the focal length f, the smaller the field of view, and the smaller the range of the picture formed on the photosensitive element; conversely, the smaller the focal length f, the larger the field of view, and the larger the range of the picture formed on the photosensitive element.

(3) F value (aperture ratio): F value refers to the brightness of the lens (that is, the amount of light transmitted by the lens). F=lens focal length/aperture diameter. For the same F value, the diameter of a long focal length lens is larger than that of a short focal length lens.

(4) Aperture: The aperture is an adjustable optical-mechanical aperture located inside the lens, which can be used to control the amount of light passing through the lens. Variable aperture (Iris diaphragm). A mechanical device inside the lens used to control the size of the aperture. Or refers to a device used to open or close the lens aperture to adjust the f-stop of the lens.

(5) Depth of field: When an object is in focus, all objects from a certain distance in front of the object to a certain distance behind it are also clear. The distance from front to back where the focus is quite clear is called depth of field.

? The full name is Voice Coil Montor, a voice coil motor in electronics, which is a type of motor. Because the principle is similar to that of a speaker, it is called a voice coil motor, which has the characteristics of high frequency response and high precision. Its main principle is to control the stretching position of the spring leaf by changing the DC current of the coil in the motor within a permanent magnetic field, thereby driving up and down movement. Mobile phone cameras widely use VCM to achieve autofocus function. VCM can adjust the position of the lens to present clear images.

? The performance of VCM mainly depends on the ratio of current and stroke distance. Starting from the starting current, the current rise must be proportional to the driving distance. The smaller the required rising current, the higher the accuracy. It also depends on the maximum power consumption, maximum power, and size.

The structure can be roughly divided into three categories: (1) shrapnel structure; (2) ball structure; (3) friction structure.

Functionally, it can be roughly divided into five categories: (1) Open loop motor; (2) Close loop motor; (3) Alternate mid-mounted motor; (4) OIS optical anti-shake motor (divided) Translation type, shift type, memory metal type, etc.); (5) OIS+Close loop six-axis motor.

? After entering the auto-focus mode, the Driver changes from 0 to the maximum value, causing the lens to move from the original position to the maximum displacement. At this time, the sensor imaging surface automatically takes pictures and saves them to the DSP. The DSP uses these Picture, calculate the MTF (Modulation transfer function) value of each picture, so as to find the maximum value in this MTF curve, and use the algorithm to obtain the current size corresponding to this point, and once again instruct the Driver to provide this current to the voice coil. Stabilizing the lens on this imaging plane enables automatic zooming.

A: Optical zoom uses a zoom motor (ZOOM)

By moving the lens inside the lens, the position of the focus is changed, the length of the focal length of the lens is changed, and the angle of view of the lens is changed. In this way, the impact can be amplified and reduced.

B: A focus motor (AF) is used to achieve autofocus.

Move the position of the entire lens (rather than the lens within the lens) over a micro distance to control the length of the lens focal length. The clarity of the image. A commonly used method in mobile phones.

Optical focus and optical zoom are different concepts:

Optical zoom changes the position of the focus by moving the relative position of the lens inside the lens, changes the length of the focal length of the lens, and changes the focal length of the lens. The size of the angle of view, thereby achieving the magnification and reduction of the image;

Optical focus actually adjusts the position of the entire lens (rather than the position of the lens within the lens) to control the image distance, so as to maximize the imaging Clear.

? There are various wavelengths of light in nature. The wavelength range of light recognized by the human eye is between 320nm-760nm. The human eye cannot see light exceeding 320nm-760nm; and the imaging components of the camera CCD or CMOS can see most wavelengths of light. Due to the participation of various lights, there is a color deviation between the color restored by the camera and what is seen by the naked eye. For example, green plants turn gray, red pictures turn light red, black turn purple, etc. At night, due to the filtering effect of the bimodal filter, the CCD cannot make full use of all light, does not produce snowflake noise, and its low-light performance is unsatisfactory. To solve this problem, use the IR-CUT dual filter.

? The IR-CUT dual filter refers to a set of filters built into the camera lens set. When the infrared sensing point outside the lens detects the change in light intensity, the built-in IR-CUT The automatic switching filter can automatically switch according to the intensity of external light, so that the image can achieve the best effect. In other words, the dual filters can automatically switch filters during the day or night, so you can get the best imaging effect regardless of the day or night.

? IR CUT dual filter switcher consists of an infrared cut-off low-pass filter (an infrared cut-off or absorption filter) and a full-spectrum optical glass (a full-spectrum filter) , a power mechanism (which can be an electromagnetic, motor or other power source) and a casing, which is switched and positioned through a circuit control board. When there is sufficient light during the day, the circuit control board drives the switch to switch and position the infrared cut-off filter to work, and the CCD or CMOS restores the true color; when the visible light is insufficient at night, the infrared cut-off filter automatically moves away, and full-spectrum optics The glass starts to work. At this time, it can sense the infrared light of the infrared lamp, allowing the CCD or CMOS to make full use of all the light, thereby greatly improving the night vision performance of the infrared camera, and the entire picture will be clear and natural.

a. The infrared cutoff degree of the filter, the light transmittance, and the light shaping effect, etc.

b. Power drive part

c. Control circuit

4. Filter: Generally, IR Coating or blue glass is used to filter. Remove infrared light.

? Image sensor (image sensor) is a semiconductor chip with millions to tens of millions of photodiodes on its surface. The photodiodes generate charges when exposed to light and convert the light into electrical signals. Its function is similar to the human eye, so the performance of the sensor will directly affect the performance of the camera.

Photosensitive originals: CCD, CMOS (PPS and APS)

Different processes: front-illuminated FSI, back-illuminated BSI, stacked

1. Pixel

There are many photosensitive units on the sensor, which can convert light into electric charges to form an electronic image corresponding to the scene. In the sensor, each photosensitive unit corresponds to a pixel (Pixels). The more pixels, it means that it can sense more object details, so the image is clearer. The higher the pixels, the clearer the imaging effect. The product of the camera resolution is the pixel value, for example: 1280×960=1228800

2. Target surface size

? The size of the photosensitive part of the image sensor, generally expressed in inches. Like a TV, this data usually refers to the diagonal length of the image sensor, such as 1/3 inch. The larger the target surface, the better the light transmission, and the smaller the target surface, the easier it is to obtain. Greater depth of field.

3. Sensitivity

? It is to sense the intensity of incident light through CCD or CMOS and related electronic circuits. The higher the sensitivity, the stronger the sensitivity of the photosensitive surface to light, and the higher the shutter speed. This is especially important when shooting sports vehicles and monitoring at night.

4. Electronic shutter

? It is a term proposed in comparison with the mechanical shutter function of the camera. It controls the photosensitivity time of the image sensor. Since the photosensitivity value of the image sensor is the accumulation of signal charges, the longer the photosensitivity, the longer the signal charge accumulation time, and the greater the amplitude of the output signal current. The faster the electronic shutter, the lower the sensitivity, which is suitable for shooting under strong light.

5. Frame rate

? It refers to the number of pictures recorded or played per unit time. Continuously playing a series of pictures will produce an animation effect. According to the human visual system, when the playback speed of the pictures is greater than 15 frames/second (i.e. 15 frames), the human eye will basically not be able to see the jump of the pictures; when it reaches 24 frames /s——When between 30 frames/s (that is, 24 frames to 30 frames), the flicker phenomenon is basically undetectable.

? Frames per second (fps) or frame rate represents the number of times a graphics sensor can update per second while processing a field. A high frame rate results in a smoother, more realistic visual experience.

6. Signal-to-noise ratio

? It is the ratio of signal voltage to noise voltage. The unit of signal-to-noise ratio is expressed in dB. Generally, the signal-to-noise ratio value given by the camera is the value when the AGC (automatic gain control) is turned off, because when the AGC is turned on, the small signal will be improved, causing the noise level to increase accordingly.

? The typical value of the signal-to-noise ratio is 45-55dB. If it is 50dB, the image has a small amount of noise, but the image quality is good; if it is 60dB, the image quality is excellent and there is no noise. The signal-to-noise ratio The larger the ratio, the better the noise control. This parameter is related to the number of noise points in the image. The higher the signal-to-noise ratio, the cleaner the picture feels, and the less point-like noise in the night vision picture.

? Digital signal processor DSP (DIGITAL SIGNAL PROCESSING) function: mainly through a series of complex mathematical algorithm operations, optimize the digital image signal parameters, and transmit the processed signal through USB and other interfaces Passed to PC and other devices

Glossary: ??

ISP is the abbreviation of Image Signal Processor, which is also an image signal processor.

DSP is the abbreviation of Digital Signal Processor, which is also a digital signal processor.

Function explanation:

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, bad pixel removal, Auto Black Level, Auto White Level and other functions.

DSP has more functions. It can do photography and echo (JPEG codec), video recording and playback (Video codec), H.264 codec, and many others. In terms of processing, in short, it is processing digital signals.

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