Understanding Camera Module Interfaces: A Guide to Choosing the Right One

Supertek2022

Introduction

The progress in the fields of semiconductors, electronics, and camera modules has given birth to the field of embedded vision systems. Today, embedded vision systems are widely used in many sectors and applications including autonomous vehicles, security systems, industrial automation, medical imaging, and robotics. Camera modules capture and transmit visual information in an embedded vision system and therefore, are crucial for the overall performance of the system. In this article, we will explore different types of camera module interfaces for embedded vision applications including MIPI CSI-2, USB 2.0, USB 3.0, and GMSL. We will discuss the pros and cons of each of these interfaces and, will help you in selecting the right camera module for your embedded vision application.

MIPI CSI-2 interface

MIPI CSI-2 is an abbreviation for Mobile Industry Processor Interface Camera Serial Interface Type-2. MIPI CSI-2 is a high-speed serial interface designed for transmitting image and video data from mobile camera modules to embedded processors. MIPI CSI-2 is amongst the most widely used interfaces in mobile phones, tablets, and handheld embedded devices. MIPI CSI-2 supports the peak bandwidth of 6 Gbps with a realistic bandwidth of 5 Gbps. The maximum supported cable length is 30 cm.

History of MIPI CSI-2 Camera Interface

The history of MIPI CSI-2 interface can be traced back to the late 1990s and early 2000s, when the mobile industry was in its early stages of development. As mobile devices became more advanced, there was a growing need for efficient and reliable protocols for transmitting multimedia data between the camera and the host processor. MIPI Alliance, a group of leading mobile industry players, was established in 2003 to address these needs.

One of the key initiatives of the MIPI Alliance was the development of the MIPI Camera Serial Interface (CSI) specification. The first version, CSI-1, was released in 2005 and quickly became the standard for camera interfaces in mobile devices.

MIPI CSI-2 interface is the enhanced version of MIPI CSI-1 interface, which was introduced in 2010 to meet the increasing demand for high-definition multimedia and higher bandwidth in mobile devices. Since then, it has become the most widely adopted camera interface in the mobile industry and continues to evolve to meet the changing needs of the industry. Today, MIPI CSI-2 is used in a wide range of mobile devices, including smart-phones, tablets, laptops, and wearable devices.

Advantages and Disadvantages of MIPI CSI-2 Camera Interface

The key advantages and disadvantages of MIPI CSI-2 interface are listed as following:

Advantages:

High-Speed Data Transfer: MIPI CSI-2 supports high-speed data transfer (up to 1 Gbps per lane), making it suitable for high-resolution image and video capture.
Low Power Consumption: MIPI CSI-2 is designed for low power consumption, making it ideal for battery-powered embedded devices.
Scalability: MIPI CSI-2 supports multiple data lanes, making it easy to scale the data transfer rate as needed.
High Reliability: MIPI CSI-2 uses differential signaling scheme, which provides better noise immunity.

Disadvantages:

Limited Distance: The maximum supported distance is only a few meters which limit the capabilities of MIPI CSI-2 interface.
Cost: MIPI CSI-2 requires specialized components, which can add to the cost of the embedded system.

USB 2.0 & 3.0 interface

USB (Universal Serial Bus) is a widely used data transfer protocol in computing devices and embedded systems. In embedded vision systems, USB 2.0 and 3.0 protocols are commonly used for transferring image and video data from the camera sensor to the host processor. USB 2.0 interface supports a maximum data transfer rate of 480 Mbps while USB 3.0 interface supports a maximum data transfer rate of 5 Gbps.
USB 2.0 and 3.0 camera interfaces are widely used in embedded vision applications including surveillance systems, industrial inspection, and machine vision. USB camera interfaces are particularly suitable for low-cost and low-power applications. The plug-and-play capability is one of the biggest advantages of USB camera interface.

Advantages and Disadvantages of USB 2.0 & 3.0 Camera Interface

Advantages:

Compatibility: The main advantage of USB 2.0 & USB 3.0 camera modules is their widespread compatibility and ease-of-use.
Low Cost: USB 2.0 and 3.0 offer low-cost solution for the transmission of image/video data in embedded vision systems.
Built in Power Supply: USB 2.0 & 3.0 both provide power to the camera module, eliminating the need for an external power supply.

Disadvantages:

Limited Length: The USB 2.0 and 3.0 camera interfaces support a maximum cable length of 5m which restricts their capabilities.
Absence of dedicated video streaming: USB 2.0 & 3.0 interfaces do not provide a dedicated video stream, meaning that image data may be delayed or lost during transmission.

GMSL Interface

Gigabit Multimedia Serial Link or GMSL is a high-speed serial link protocol for the transmission of image/video data in embedded vision systems. GMSL provides a fast and reliable connection between the camera sensor and the host processor. GMSL uses differential pair for data transmission which increases noise immunity and data integrity. GMSL uses a unique encoding scheme which reduces the EMI (electromagnetic interference) and allows for longer cable lengths and higher data rates as compared to the traditional serial link camera interfaces.

GMSL finds its applications in a variety of embedded vision systems such as ADAS (advanced driver assistance system), autonomous vehicles, and quality control systems. GMSL is particularly suited for applications requiring high bandwidth, high reliability, and long transmission distances.

Advantages and Disadvantages of GMSL Camera Interface

Advantages:

Long Distance Communication: One of the key advantages of GMSL is its ability to support high data rates over long distances, typically up to 15 meters.
Higher Reliability and Data Integrity: It also provides a robust and reliable connection, as well as low latency and jitter, making it well-suited for applications that require real-time image and video data transmission.
Scaling: GMSL supports multiple data lanes, allowing for easy scaling of the data transfer rate as needed.

Disadvantages:

Higher Cost: One of the main disadvantages of GMSL is that it can be more expensive compared to other camera module interfaces, such as USB.
Complexity: The GMSL protocol requires specialized hardware and software, making it less accessible for novice users.

How to choose the right interface for an embedded vision system?

The selection for right camera module interface for an embedded vision application depends on a number of factors which are listed as following:

Data Transfer Rate: This is one of the most important considerations while selecting an embedded camera interface. MIPI CSI-2 offers the highest data transfer rate of 6 Gbps, USB 3.0 supports up to 5 Gbps, and USB 2.0 supports up to 480 Mbps. GMSL can support data rates up to 12 Gbps with multiple data lanes.
Cable Length: The maximum cable length supported by the interface is another important consideration. MIPI CSI-2 supports a maximum cable length of 30 cm, while GMSL supports cable lengths up to 15 meters. The cable length of USB 2.0 and USB 3.0 is determined by the maximum transfer speed and the quality of the cable. The maximum cable length for USB 2.0 is 5 meters, while for USB 3.0, it is 3 meters, due to the higher speed of USB 3.0. Longer cables can negatively affect the speed and quality of data transfer for both USB 2.0 and USB 3.0. It’s worth noting that the actual usable cable length may be shorter in practice, depending on the cable quality and environment.)
EMI (Electromagnetic Interference): GMSL uses a unique encoding scheme that reduces EMI, making it suitable for applications that require longer cable lengths. MIPI CSI-2, USB 2.0, and USB 3.0 are also capable of reducing EMI, but to a lesser extent.
Power Requirements: Power consumption is one of the most crucial requirements for handheld and mobile embedded devices. Consider the power requirements of your camera module and choose an interface that can provide the required power. GMSL and MIPI CSI-2 support high-resolution cameras that require a lot of power and allow for customization of power to meet specific camera requirements. The choice of interface and power requirements will ultimately depend on the needs of the camera and the device it will be connected to.)
Cost: Cost is perhaps the most important consideration for the selection of hardware and camera interface for an embedded vision application. USB 2.0 and USB 3.0 are often the most cost-effective options, but the cost of the interface will depend on the specific components used.

Conclusion

In this article we have explored different types of camera module interfaces for embedded vision applications, including MIPI CSI-2, USB 2.0, USB 3.0, and GMSL. The pros and cons of each interface were discussed to help the readers in selecting the right camera module interface for their embedded vision application. MIPI CSI-2 is a high-speed serial interface for transmitting image and video data, but with limited distance. USB 2.0 & 3.0 offer wider compatibility and low-cost, but have limited length and absence of dedicated video streaming. GMSL offers high-speed and high-bandwidth serial interface, but with limited compatibility and higher cost. Therefore, the selection of the right camera module interface is a trade-off between multiple factors including cost, performance, support, bandwidth, and transmission distance.