Impact of space ray-neutron on automotive electronic equipment

Imagine: If you drive on the highway at 75 miles per hour, drive a new car that was purchased in 2006, while enjoying Steve Miller's Greatest Hits. Suddenly, the engine management system or the stability control system failed.

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If this happens, you may not only encounter a serious or potentially fatal car accident, but the car factory may also be ruined, assuming that the situation is more than one.

Design engineering is now facing more and more challenges as cars move from purely mechanical equipment to modern, highly integrated, line-driving automotive electronics systems. They must continue to add complex electronic equipment to every subsequent model year, while still maintaining high standards of quality and reliability, and meeting stringent low cost and high volume production requirements.

Traditionally, these developers have used microcontrollers (MCUs), ASICs, and large harnesses to implement and control these systems and extend the performance of each generation. At present, these technologies have approached their limits and have raised concerns about reliability issues due to the exponential growth in complexity. To solve these problems, many design engineers are turning to FPGAs as a flexible and low-cost solution for next-generation automotive electronics design.

Space ray-induced failure

In order to ensure that the functions of various systems in modern cars are functioning properly, reliability data requirements must be placed on components. Although people master most of the principles of component reliability, in the process of selecting programmable logic devices such as FPGAs, some unique issues should be included in the factors that should be considered.

Specifically, technical decision makers anticipate sources of failure that will affect the programmable logic system. Although the concept of neutron bombardment from space (cosmic rays) sounds like an episode of Star Trek, the errors caused by neutrons are actually harmful to many types of electronic devices.

The neutron-induced firmware error has changed from a troublesome matter to a major problem. For example, if a neutron causes an SRAM (static-based) FPGA-based (SRAM FPGA) hive to be disturbed, it may result in loss of functionality. If this happens, it can cause the main system to malfunction. Looking ahead, this problem will be even more serious, as future deep sub-micron manufacturing processes will continue to present real challenges for design engineers of FPGA-based automotive electronic systems.

Single Event Interference (SEU) caused by neutrons within an integrated circuit may occur in various types of non-volatile memory cells. The above SRAM FPGA uses internal memory cells to maintain the configuration state or (personality) of the FPGA. These memory units face a more serious reliability threat. When the content is changed, it is called a "soft error" because it is a data error and the function is not affected. Although the device can be successfully rewritten with the correction data, EDAC (Error Detection and Correction) or TMR (Tunnel Reluctance) can be used for the SRAM data and registers, respectively. Soft errors can result in data loss or "unexpected system failure."

If the SRAM FPGA configuration memory unit is corrupted, it is called a "firmware error" because these errors are not easily detected or corrected and are not transient in nature. Once a firmware error occurs in the FPGA, the device must be reloaded with the initial configuration. In some cases, you must power cycle to clear the fault and then reconfigure it.

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In these configuration units, as long as there is a SEU caused by neutrons, the consequences are serious. If configured to be disturbed and change state, it can change the functionality of the entire device, causing significant data corruption or sending false signals to other circuits in the system. In extreme cases, if a firmware error has not been detected for a long time, it can become "hard errors" and cause damage to the device itself or to the system containing the device. A common example of this type of problem is that a steady fault caused by a neutron directs the signal to the wrong path, causing a short circuit.

For automotive electronic applications that use SRAM FPGAs to perform mission-critical tasks, neutron-induced errors have a major impact. The existing detection technology reads back the configuration of the FPGA at regular intervals, which is not helpful to prevent errors in the system.

In addition, the readback circuit capable of detecting a corrupted configuration is itself susceptible to SEU or damage. Furthermore, in examining the errors caused by anti-neutrons in automotive systems, with the widespread application of susceptible FPGA technology, it is required to add an innovative quality certification system to the AEC-Q100 standard to complement the JEDEC standard 89. insufficient. Current approaches to detecting and correcting FPGA firmware errors add additional complexity to the system design and increase board size and material cost, increasing the "cost" of errors caused by neutrons.

Firmware errors caused by neutrons can have a significant impact on the time-calculated failure (FIT) rate of the entire system. Because it is difficult to detect and is almost impossible to diagnose, soft and stable failures can cause maintenance and service problems, which can result in increased warranty costs. Among the three mainstream FPGA technologies—anti-fuse, flash, and SRAM—only anti-fuse and flash memory are protected from soft errors and firmware errors caused by neutron resistance.

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Example: Automotive System with SRAM FPGA

This example analyzes a system that is installed in the floor of a cab. The neutron ray density is calculated in Denver, and the elemental cobalt is placed at a height of 5,000 feet and measured using SpaceRad 4.5, a widely used radiation effect prediction software program. Based on published radiation data for 0.22um SRAM FPGAs, the predicted perturbation rate per 1 million gates per day is 1.05E-4.

If the vendor deploys 1 million SRAM FPGAs in the occupant sensor and airbag control module, multiply the disturbance rate of 1.054E-4 per 1 million gates per day by the disturbance rate of 4.38E-06 per system per day or 4375FIT. This means that if the same vendor uses a safety system based on 1 million SRAM FPGAs in 500,000 vehicles, multiplying the number of disturbances by 1.05E-4 by the number of vehicles/systems on the road, you get 52.5 for all vehicles per day. The total number of disturbances (assuming the vehicle is working at constant speed).

This is equivalent to a disturbance every 27.4 minutes. Even for medium vehicle usage for two hours a day, there are still two disturbances per day. Because these are stable faults, they will continue until the SRAM FPGA is reloaded (usually to power up or force configuration).

In current semiconductor technology, soft errors in devices have received a lot of attention. As device sizes continue to shrink, it is widely believed that these soft errors will be a major issue. These errors can often greatly reduce the availability of the system. In order to maintain the availability of the system at an acceptable level, there is a strong desire to avoid soft errors.

Future work to do

When choosing an FPGA, it is critical to evaluate the total cost of ownership of each programmable architecture and identify suppliers with inherently reliable core technology, not to use second-class quality designed for low-level applications. Commercial products.

For design engineers using SRAM FPGAs, it is necessary to implement circuits that detect and correct configuration errors, although this adds to system cost and complexity. In addition, radiation test data indicates that anti-fuse and flash-based FPGAs are less prone to configuration loss due to neutron-induced disturbances. This makes them especially suitable for applications with high reliability requirements.

Now imagine the slightly different location: You drive the new 2006 model on the highway at 75 miles per hour, listening to the beautiful Steve Miller's Greatest Hits. With confidence in the non-volatile flash-based FPGAs used in the engine management system, you can accelerate your rides, experience the joy of speed, and enjoy comfortable and trouble-free travel.

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