Analysis of the development of mobile phone camera sensors

I remember that when the mobile phone just had a camera, I was excited about the editor, because at that time, I never thought about the ability of the mobile phone to take pictures. Until now, the pixels of the mobile phone camera are getting higher and higher, and the picture quality is getting better. It's getting better and better, some even add optical image stabilization and optical zoom like SLR cameras, so what is the structure of that small camera?

We all know that the most important part of whether a mobile phone or a camera determines its imaging quality belongs to the photosensitive element. There are two main types of photosensitive element, one is a CCD sensor and the other is a CMOS sensor.

Among them, the CCD imaging quality is good, but the manufacturing process is complicated, the number of manufacturers that can be produced is relatively small, the price is relatively high (the rare thing is expensive), and the power consumption is also very high, so it is not suitable for mobile devices use.

The power consumption of CMOS sensors is low, but the image quality is not as good as CCD. However, with the improvement of technology, the image quality of COMS has gradually caught up with CCD. In addition, at the same resolution, CMOS is cheaper than CCD, so at present Mobile phone cameras on the market all use CMOS sensors.

CMOS sensors are usually divided into: back-illuminated CMOS sensors and stacked CMOS sensors.

The so-called back-illuminated CMOS sensor is actually opposite to the traditional front-illuminated CMOS sensor. Simply put, the photodiode and the wiring layer are reversed (as shown above), so that the light first enters the photodiode, thereby increasing the amount of light and significantly improving the shooting effect under low light conditions. Like the iPhone4 / 4S, Xiaomi 2S, Meizu MX2, and Sony LT26i that we are all familiar with, these sensors are equipped.

The stacked CMOS sensor is a derivative of the back-illuminated CMOS sensor. It is currently the most widely used and the most advanced of mobile phone cameras, and belongs to Sony's exclusive technology.

The stacked CMOS sensor uses a chip with a signal processing circuit to replace the support substrate of the original back-illuminated CMOS image sensor. The pixel portion of the back-illuminated CMOS element is formed on the chip (above: â‘  + â‘¡ = â‘¢). The process of forming a large number of pixels on a smaller chip size. Since the pixel portion and the circuit portion are independent, the pixel portion can be optimized for high image quality, and the circuit portion can be optimized for high performance.

Finally, the editor wants to say that the photosensitive element is only an indispensable part of the composition of the mobile phone camera, but it is not a decisive factor for the imaging quality of a mobile phone. This also includes the optimization of hardware by the manufacturer through software to make it Feel the best effect (this involves the feelings of different people, it depends on the manufacturer's positioning of the product), which is also one of the most decisive factors for the difference in the quality of mobile phone camera quality among various manufacturers.

Here are some common questions about mobile phone cameras.

Why is the camera lens round? The light sensor inside is obviously square.

This is because the circle can reach the largest imaging area; on the other hand, it has many optical advantages, such as the side of the circle can reduce the reflection of light; moreover, the round lens is more convenient to grind, The assembly can be done more accurately, and it is easy to make various fine adjustments.

The most important thing is also in the mechanical structure: including fine adjustment of focus and zoom, it is most convenient to use the spiral propulsion, and the rotation of the round lens will not cause the loss of imaging (if it is a rectangular lens, then turn 90 °, 3 * 2 rectangular photos are cut into 2 * 2 squares) to facilitate the setting of various adjustment mechanisms.

Medium and large format lenses need to be matched with different sizes of film / photosensitive elements. Maximizing as much as possible is naturally the most material-saving method (shaped lenses, such as spectacle lenses, are actually cut from round lenses. For lenses Generally speaking, cropping is not helpful for imaging, but instead of changing the film, the imaging range may not be enough, which is typically not easy.)

What is the principle of the application of the finger placed in front of the mobile phone camera and the flash to detect the heart rate?

Highlight the light (LED flash next to the camera, or other bright enough light source) to illuminate the capillaries under the fingertips. When the heart presses fresh blood into the capillaries, the brightness (red depth) will change slightly. The camera monitors this regularly changing interval to calculate the heartbeat.

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