By Onn Haran

In order for a Vehicle-to-Vehicle Communication (V2X) sensor to detect a car behind the corner, it should work reliably. One of the unique requirements of the Automotive market is the high operating temperature. While a typical consumer product is graded for 70ᵒ ambient temperature operation, the lowest Automotive-grade (AEC-Q100 grade 3) should operate at 85ᵒ. The requirement is raised to 105ᵒ (AEC-Q100 grade 2) when the electronic unit is placed above the roof, at the antenna, or below it, at the headliner.

Vehicles should operate on the hottest summer days with minimal wind flow and no shade. A dark color roof can reach very high temperatures when the vehicle is parked in the sun, or slowly progressing in a traffic jam. A chip not designed to work at high temperatures will suffer reliability degradation, shortening its lifetime. For this reason, all carmakers take temperature requirements very seriously.

A V2X subsystem includes multiple building blocks: radio, modem, security signing (HSM) and verification, and a high-capacity CPU for processing. All these blocks should operate at high temperatures. When a system is composed of multiple chips, the chip with the lowest operating temperatures sets the V2X limit of operation. 

Multiple methods can be considered in order to increase a system’s operating temperature:

• Thermal efficient package: One possible solution is embedding a metal slug in the package, at the expense of a cost increase.
• Larger packaging: Increasing package size cannot realistically be considered due to the size constraints, particularly in the case of TCU or antenna installation. Larger packaging also increases the cost.
• Thermal management: A heat sink improves thermal dissipation while complicating the mechanical design and increasing cost. When a heat sink isn’t enough, a fan is required. The cost impact is significantly higher and a single point of failure is introduced. This point of failure is troubling considering the contribution of V2X to vehicle safety, which will increase in the upcoming years.
• Low-duty cycle operation: Wireless standards commonly reduce the operation cycle by limiting the communication to specific slots. For example, cellular communication applies Discontinuous Reception (DRX) turning off the receiver for a couple of seconds while communication is idle. This isn’t applicable to V2X. A safety-critical message can arrive at any given moment, and the receiver should be ready with minimal latency. In addition, in C-V2X, the channel should be constantly scanned to determine the transmitter resource allocation.
• Specifically designed for high-temperature: This involves a silicon process with high junction temperature and applying low-power design techniques. The chip should be simulated and tested at high temperature and voltage corners.

The first three methods (thermal efficient package, enlarged packaging and thermal management) incur a cost penalty. The fourth method (low-duty cycle operation) is not applicable. That leaves the fifth method (high-temperature thermal design) as the only robust and cost-efficient solution. Tier1s do not need to increase the design cost, risk, and complexity by adding thermal management.

A chip designed as a consumer cellular modem and used for V2X without being specifically designed for high-temperature operation will be at a high risk of failing temperature requirements in a real operating environment.

Autotalks chipsets are rigorously designed for high operating temperatures. They can be used in an antenna or headliner without any thermal management. The high-integration level assures that all building blocks, radio, modem, security and processing can sustain a sunny day in the desert in a black car.