MIPI Camera vs USB Camera
Over the past few years, embedded vision has evolved from a buzzword to a widely adopted technology used across industrial, medical, retail, entertainment, and farming sectors. With each phase of its evolution, embedded vision has ensured a significant growth in the number of camera interfaces available to choose from. However, despite the technological advancements, MIPI and USB interfaces have remained the two most popular types for a majority of embedded vision applications.
MIPI Interface
MIPI (Mobile Industry Processor Interface) is an open standard and a specification initiated by the MIPI Alliance for mobile application processors. MIPI camera modules are commonly found in mobile phones and tablets, and support high-definition resolutions of more than 5 million pixels. MIPI is divided into MIPI DSI and MIPI CSI, which correspond to video display and video input standards, respectively. At present, MIPI camera modules are widely used in other embedded products, such as smartphones, driving recorders, law enforcement cameras, high-definition micro cameras, and network surveillance cameras.
MIPI Display Serial Interface (MIPI DSI ® ) defines a high-speed serial interface between a host processor and a display module. The interface enables manufacturers to integrate displays for high performance, low power consumption, and low electromagnetic interference (EMI), while reducing pin count and maintaining compatibility between different suppliers. Designers can use MIPI DSI to provide brilliant color rendering for the most demanding image and video scenarios and support the transmission of stereoscopic content.
MIPI is the most commonly used interface in today’s market for point-to-point image and video transmission between cameras and host devices. It can be attributed to MIPI’s ease of use and its ability to support a broad range of high-performance applications. It also comes equipped with powerful features such as 1080p, 4K, 8K and beyond video and high-resolution imaging.
MIPI interface is an ideal choice for applications like head-mounted virtual reality devices, smart traffic applications, gesture recognition systems, drones, facial recognition, security, surveillance systems, etc.
MIPI CSI-2 Interface
The MIPI CSI-2 (MIPI Camera Serial Interface 2nd Generation) standard is a high-performance, cost-effective, and simple-to-use interface. MIPI CSI-2 offers a maximum bandwidth of 10 Gb/s with four image data lanes – each lane capable of transferring data up to 2.5 Gb/s. MIPI CSI-2 is faster than USB 3.0 and has a reliable protocol to handle video from 1080p to 8K and beyond. In addition, owing to its low overhead, MIPI CSI-2 has a higher net image bandwidth.
The MIPI CSI-2 interface uses fewer resources from the CPU – thanks to its multi-core processors. It is the default camera interface for Raspberry Pi and Jetson Nano. The Raspberry Pi camera module V1 and V2 are also based on it.
Limitations of MIPI CSI-2 Interface
Even though it is a powerful and popular interface, MIPI CSI does come with a few limitations. For instance, MIPI cameras rely on extra drivers to work. It means that there is limited support for different image sensors unless embedded system manufacturers really push for it!
Advantages Of MIPI:
The MIPI interface has fewer signal lines than the DVP interface. Because it is a low-voltage differential signal, the interference generated is small, and the anti-interference ability is also strong. 800W and above all use MIPI interface. The smartphone camera interface uses MIPI.
How it works?
Typically, the ultra-compact board in a vision system supports MIPI CSI-2 and works with a high range of intelligent sensor solutions. Moreover, it is compatible with many different CPU boards.
MIPI CSI-2 supports the MIPI D-PHY physical layer to communicate to the application processor or System on a Chip (SoC). It can be implemented on either of the two physical layers: MIPI C-PHY℠ v2.0 or MIPI D-PHY℠ v2.5. Therefore, its performance is lane-scalable.
In a MIPI camera, the camera sensor captures and transmits an image to the CSI-2 host. When the image is transmitted, it is placed in the memory as individual frames. Each frame is transmitted through virtual channels. Each channel is then split into lines – transmitted one at a time. Hence, it permits complete image transmission from the same image sensor – but with multiple pixel streams.
MIPI CSI-2 uses packets for communication that include data format and error correction code (ECC) functionality. A single packet travels through the D-PHY layer and then splits into the number of required data lanes. D-PHY operates in high-speed mode and transmits the packet to the receiver through the channel.
Then, the CSI-2 receiver is provided with D-PHY physical layer to extract and decode the packet. The process is repeated frame by frame from the CSI-2 device to the host through an efficient and low-cost implementation.
USB Interface
The USB interface tends to serve as the junction between two systems – the camera and the PC. Since it is well-known for its plug-and-play capabilities, choosing the USB interface implies that you can say goodbye to expensive, drawn-out development times and costs for your embedded vision interface. USB 2.0, the older version, has significant technical limitations. As the technology begins to dwindle, a number of its components become incompatible. USB 3.0 and the USB 3.1 Gen 1 interfaces were launched to overcome the limitations of the USB 2.0 Interface.
The USB 3.0 (and USB 3.1 Gen 1) interface combines the positive features of different interfaces. These include plug-and-play compatibility and low CPU load. The vision industrial standard of USB 3.0 also increases its reliability for high-resolution and high-speed cameras.
It requires minimal additional hardware and supports low bandwidth – up to 40 megabytes per second. It has a maximum bandwidth of 480 megabytes per second. This is 10 times faster than USB 2.0 and 4 times faster than GigE! Its plug-and-play capabilities ensure that embedded vision devices can be swapped out with ease – making it easy to replace a damaged camera.
Limitations of USB 3.0 Interface
The biggest disadvantage of the USB 3.0 interface is that you cannot run high-resolution sensors at high speed. Another downfall is that you can only use a cable up to a distance of 5 meters from the host processor. While longer cables are available, they are all fitted with “boosters”. How well these cables work together with industrial cameras has to be checked for every individual case.
Post time: Mar-22-2023
