Classification and Basic Knowledge of USB Camera Interface

1. Introduction to the working principle of USB camera
The working principle of USB cameras is based on optical imaging and sensor technology, and the overall process is to convert optical images into digital image signals that can be processed by computers. Light enters the camera through the lens, which focuses the light of the scene onto the image sensor to form an optical image. The optical image is projected onto the surface of an image sensor, which generally includes two types: CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor). When light shines on the sensor pixels, it is converted into an electrical signal based on the photoelectric effect, and then the image processor converts the electrical signal into a digital signal.
2. Detailed conversion process
Photoelectric Conversion
An image sensor is a semiconductor chip with hundreds of thousands to millions of photodiodes on its surface. When these photodiodes are exposed to light, they generate charges, thereby converting light signals into analog electrical signals. For example, in CMOS sensors, it converts light signals into electrical signals on a pixel by pixel basis, and CMOS sensors are more energy-efficient and suitable for low-power applications.
analog-to-digital conversion
Analog to digital conversion (A/D) is the process of converting an analog signal into a digital signal, dividing the analog signal into discrete parts, and then representing these parts with numbers. After analog-to-digital conversion, the analog signal generated by the charge becomes a digital image signal.
3. Signal processing process
DSP chip processing
The digital signal processing chip (DSP) is a key component in cameras, which receives digital image signals from image sensors and optimizes them through a series of complex mathematical algorithms. Its structural framework typically includes components such as an image signal processor (ISP), a JPEG image decoder (JPEG encoder), and a USB device controller. DSP can adjust the brightness, contrast, color saturation, and sharpness of images to improve their quality. The main DSP manufacturers in the market include SONIX and VIMICRO.
4. Computer reception and display
Finally, the computer receives these processed digital image signals through a USB interface and displays them on the screen, allowing users to view and use them. The Universal Video Class (UVC) specification is a set of standards defined by the USB Implementers Forum (USB-IF). It provides a standard interface for data transmission between USB cameras and computers, allowing USB cameras to be recognized and used by the operating system without the need to install specific drivers, greatly simplifying the device setup and installation process.

USB camera interface classification

Common types include USB2.0 Type-A,USB 3.0 Type-A, USB Type-B,USB Mini-B,USB Micro-B,USB 3.0 Micro-B,USB Type-C
The interface used by USB cameras is mainly the physical connector defined by the USB standard. With the development of USB standards, physical interfaces are also evolving:
1. USB Type-A (Standard-A): The most common rectangular interface used to connect the host end of a computer (HUB, docking station, ports on the computer). Excellent downward compatibility.USB 3.0 Type-A (usually blue tongue) is compatible with USB 2.0/1.1 Type-A devices and ports (but with reduced speed). USB 2.0 Type-A (usually black or white tongue) is compatible with USB 1.1. The vast majority of traditional USB cameras use this interface to connect to a computer. One end of the cable is Type-A (plugged into a computer), and the other end is usually Micro-B or Mini-B (plugged into a camera). Nowadays, more and more cables are Type-C (plugged into a camera). There are positive and negative directions, but if inserted in the opposite direction, it won't fit in.
2. USB Type-B (Standard-B): Square interface, larger in size than Type-A. Mainly used to connect larger devices such as printers and scanners. Very rarely used for modern consumer grade USB cameras. It may appear on some very old or special industrial camera equipment. There are positive and negative directions.

3. USB Mini-B: A much smaller ladder interface than Type-B.
It used to be a common interface for digital cameras, portable hard drives, some old-fashioned mobile phones, and old USB cameras (popular around 2005-2015).
It has been replaced by Micro-B and Type-C and has basically disappeared on new devices. There are positive and negative directions.
4. USB Micro-B: A very flat trapezoidal interface, which is currently the most common USB interface on mobile devices besides Type-C. Widely used in old Android phones, power banks, some external hard drives, and a large number of USB 2.0 cameras.
USB 3.0 Micro-B: An additional protrusion has been added next to the standard Micro-B interface to provide the extra pins required for USB 3.0. Some newer USB 3.0 cameras may use this interface. It is still the standard interface for many USB 2.0 cameras, but is rapidly being replaced by Type-C. There are positive and negative directions, but the Micro-B plug design makes it easier to plug in than the Mini-B (with a more pronounced trapezoid).

5. USB Type-C: Compact, oval, symmetrical design.
Forward and backward insertion: There is no directionality, it can be inserted any way.
Multifunctionality: Not only used for USB data transfer, but also supports power supply (PD), DisplayPort video output, Thunderbolt 3/4 (authentication required), etc.
High bandwidth: Native support for USB 3.2 Gen 1/2 (5Gbps/10Gbps) and above speeds (USB4).
Future mainstream: It is the unified interface direction for almost all new devices (phones, laptops, tablets, peripherals) currently and in the future.
Usage: More and more high-end USB cameras (especially 4K cameras with USB 3.0/3.1/3.2 specifications) are adopting the Type-C interface (camera end).
Many new laptops only have Type-C ports and require the camera to be connected through Type-C or an adapter to be used. For users who need to purchase a new camera, especially those who require high-speed transmission (high resolution/high frame rate) or connect to a new computer, the Type-C interface (camera end) is strongly recommended.

Common Problem:
1. How to choose the appropriate interface?
Users should evaluate which interface best meets their personal needs, as each interface in the market has its own advantages and must be selected based on specific applications. For example, for high-definition or high frame rate cameras, upgrading to a USB 3.0 interface can be considered to achieve higher transmission rates and better user experience; For general usage scenarios, the USB 2.0 interface may be sufficient to meet the requirements.
2. Interface stability and reliability
When selecting a USB camera, in addition to considering the interface type, the stability and reliability of the interface itself are also important influencing factors. Users should pay attention to the connection method and cable quality of the camera to ensure stable signal transmission and good image quality. In addition, the distance between the camera and the computer also needs to be considered. If the distance is too far, signal transmission may encounter problems. In this case, wired extension cables or wireless signal expansion devices can be considered to solve the distance problem.
3. Do you need adapters and adapter cables?
In some cases, users may need to use special adapters and adapter cables to connect USB cameras. For example, Apple computers do not have a USB-A interface, and users can use a USB-C adapter to connect the camera to the computer; If the camera needs to be installed at a higher position but the USB cable length is not enough, a USB extension cable or USB signal extender can be used. When selecting adapters and adapter cables, it is important to ensure that they are compatible with the USB interface type of the camera and have reliable signal transmission and stable power supply.