10 Gbps Communications for Automotive
The automotive industry is currently seeking technologies to enable 10 Gbps communications. This derives from the growing need for data interchange between sensors and electronic control units in the car. Infotainment, ADAS and growing levels of autonomy are the key trends that explain the exponential growth of data rates: 100 Mbps to 1 Gbps and to 10 Gbps. Some OEMs are even talking about 25 and 50 Gbps for the upcoming years.
Shortcomings of 10GBASE-SR
Ideally, an existing standard would work for automotive applications. However, 10GBASE-SR has not been designed to meet stringent automotive requirements. It was originally created to meet the demands of data centers where temperature, operating life, price, reliability and mechanical robustness are very controlled and modest.
Automotive Requirement: Temperature
Most automotive use cases require AEC-Q100 grade-2 qualification. This means that ambient operating temperatures range from -40 °C to 105 °C. 10GBASE-SR does not establish any temperature range. Consequently, available commercial products do not meet automotive temperature requirements.
If 10GBASE-SR is used in an automotive environment in the high temperature range, there will be a negative impact on the maximum power that the light source (Vertical-Cavity Surface-Emitting Laser, VCSEL) can inject into the fiber. In other words, the light source will reduce its output light power at high temperatures. This translates to shorter link lengths and/or a smaller number of in-line connectors allowed.
Automotive Requirement: Reliability
Automotive applications require over 15 years of operation with close to 0 ppm failures. The current density is the main parameter affecting the VCSEL. The higher the current density, the lower the operating life of the device. Accordingly, the VCSEL’s current density needs to be reduced to meet automotive requirements in terms of reliability and lifetime. Effects include a negative impact on the maximum power that the VCSEL can inject into the fiber. Shorter links and/or a smaller number of in-liners are the consequences. In addition, transmission bandwidth is reduced, resulting in slower transmission speeds. Furthermore, relative intensity noise will increase, with the effect of lower signal-to-noise ratio and a link budget reduction.