Camera module and hardware interface of Camera1 camera

One 、Camera Module introduction

The picture of the camera structure module is as follows ：
Camera The module is mainly composed of the following parts ：

（1） working principle
   Objects pass through the lens （lens） Aggregated light , adopt CMOS or CCD The integrated circuit , Convert optical signals into electrical signals , And then through the internal image processor （ISP） It is converted into a digital image signal and output to a digital signal processor （DSP） Processing , Convert to standard GRB、YUV Equal format image signal .
（2）CCM It contains four pieces
   The lens （lens）、 sensor （sensor）、 Soft plate （FPC）、 Image processing chip （DSP）.
   The components that determine the quality of a camera are ： The lens （lens）、 Image processing chip （DSP）、 sensor （sensor）.
The lens （lens）：
   Lens is the soul of camera , The lens （lens） It plays an important role in imaging effect , It uses the refraction principle of the lens , The scene light passes through the lens , Form a clear image on the focus plane , Through photosensitive materials CMOS or CCD The photoreceptor records the image of the scene .
sensor （sensor）：
   Sensor is CCM Core module , At present, there are two widely used ：
   One is CCD（ Charge coupling ） Components ;
   The other is CMOS（ Complementary metal oxide conductor ） device .
Image processing chip （DSP）：
  DSP yes CCM An important part of , Its function is to transmit the data obtained by the photosensitive chip to the central processing unit in time and quickly and refresh the photosensitive chip , therefore DSP The quality of the chip , Directly affect the quality of the picture （ Such as color saturation 、 Clarity, etc ）.
（3） Image processing format
①YUV：
  “Y” Indicates brightness （Luminance、Luma）,“U” Said the chromaticity （Chrominance）,“V” Indicates the concentration （Chroma）. In general sensor Support YUV422 Format is by Y-U-Y-V Sequential output .
②JPEG：
   As a storage format, it is very common , But as a sensor The output format of , Generally low resolution comes with JPEG engine, You can directly output compressed jpg Format data .
③RGB：
   Traditional red and blue format , Such as RGB565. Generally speaking, its color mixing method seems to have red 、 green 、 Three blue lights , When their light overlaps with each other , Mix colors , The brightness is equal to the sum of the two brightness , The brighter the mixture is , That's additive mixing .
④RAW：
   The image sensor converts the captured light source signal into the original data of the digital signal .RAW A file is a record of the original information of a digital camera sensor , At the same time, some original data generated by camera shooting are recorded （Metadata, Such as ISO Set up 、 shutter speed 、 Aperture value 、 White balance and so on ） The file of .RAW It's unprocessed 、 Also uncompressed format , You can put RAW Conceptualized as “ Raw image encoded data ” Also known as “ Digital film ”.

Different output formats , Contains data of different sizes ：
   First , If the amount of data is the smallest , Then nothing is better than RAW Format , however , The information in the data can only be extracted after a large amount of calculation at one time , If you want to use , commonly 5M The above senseor Just output RAW Data to ensure faster output speed , Hang one at the back end DSP To process the output data . The second is JPEG, The amount of data is also very small , But it also requires faster processing speed . and RGB and YUV One pixel is occupied 2B Size , however RGB But the data can be read out and directly displayed on the screen .
Why choose YUV Format ？
   The reason lies in YUV The output brightness signal has no loss , The human eye is not particularly sensitive to color shift signals ,RGB565 The output format is R5、G3、B5 Will lose a lot of original information , therefore YUV Image quality and stability are better than RGB565 Much better .
（4） Relationship between sensor size and image quality
   The influence of sensor size on image quality , It's the same as before , Is the difference between the correctness and integrity of the collected light data . With the same pixels ：
① The larger the sensor area , The larger the area of the photosensitive array , The greater the distance between adjacent photosensitive circuits , The smaller the electromagnetic interference generated when the power is on .
② The larger the sensor area , The larger the area of the photosensitive array , The larger the lens corresponding to a high single pixel , The more light it gathers , The higher the output level of the photodiode after receiving light . Assume that the noise level is constant , Then a larger useful output level , Higher signal-to-noise ratio , The higher the accuracy of the converted information processing .
③ Why when the light is very good , The difference between sensor sizes will be reduced ？ Because even if the sensor is small , But the light is strong enough , Each photodiode receives enough light , The greater the signal-to-noise ratio , The noise is reduced .
（4） Image resolution 、 The resolution of the （Resolution）

QSIF/QQVGA	160 x 120	19200
QCIF	176 x 144	25344
SIF/QVGA	320 x 240	76800
CIF	352 x 288	101376	10 Mega pixels
VGA	640 x 480	307200	30 Mega pixels （35 Ten thousand means 648 x 488）
SVGA	800 x 600	480000	50 Mega pixels
XGA	1024 x 768	786438	80 Mega pixels
SXGA	1280 x 1024	1320720	130 Mega pixels

Two 、Camera Hardware interface

1、camera The hardware interface of is shown in the figure below ：

It mainly consists of the following five parts , Working together ：
（1） Three way voltage AVDD/DVDD/IOVDD：
  AVDD Analog power , Mainly for sensitive areas and ADC Partial power supply , It should be clean ;
  DVDD Digital power supply , Mainly for ISP Part of the power supply ;
  IOVDD Numbers IO Power Supply , to I2C and DVP Partial power supply .
（2）PDN/RST：
  RST： be used for reset sensor;RESET Generally, it is low effective , When the pulse is low ,reset sensor, And in normal operation , Should be high .
   The reset sequence is usually : high –> low –> high , Add a certain delay according to hardware requirements ;
  PWN：PWN Generally highly effective , When the pulse is high , Enter power saving mode , It is low in normal operation . High voltage usually , Everything is right camera All operations are invalid , Including reset . So in RST Before , Be sure to will PWN The pin is set to the normal operating mode , Otherwise, reset is invalid .
（3）I2C Control interface SCL/SDA.
（4）MCLK The clock is used to divide the frequency to others clk Use .
（5）mipi Interface RCP/RCN、RDP/RDN.
2、camera The work sequence of ：
camera Power on sequence during operation , Follow exactly datasheet The above sequence and time interval ：
Again camera The same is true of the power down sequence ：