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Using EDAC RAM for RadTolerant RTAX-S/SL and Axcelerator FPGAs

Posted: 06 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:RAM? FPGAs Axcelerator? RTAX-S/SL RadTolerant?

The newest Actel designed-for-space FPGA family, RTAX-S/SL, is a high-performance,

high-density, antifuse-based FPGA with embedded user static RAM (SRAM). Based on the new Actel AX architecture, the RTAX-S/SL family is the high-reliability version of its commercial counterpartthe Axcelerator FPGA family. RTAX-S/SL is single event upset (SEU)enhanced, specifically designed for space, and contains embedded triple modular redundancy (TMR) registers, transparent to the user, which provide protection against heavy ions. In space applications, storage elements like SRAMs are susceptible to the impact of heavy ions from cosmic galactic rays (CGRs). CGRs can collide with the silicon lattice of a RAM cell with sufficient photovoltaic energy to produce a change of state, thus invalidating the stored data and producing bit errors. These errors are called soft errors.

There are several ways to implement static RAM in space devices. One option is to do nothing to mitigate soft errors. This is acceptable if the quality of the data stored in the SRAM is insensitive to single-bit changes, such as an image comprising millions of pixels or a streaming video feed. However, it is not acceptable if data is sensitive to single-bit changes, such as communication packet headers. Another option is to implement a special hardened SRAM circuit. This consumes more chip real estate and may require custom or boutique processing, and therefore is an expensive proposition.

Actel has chosen to use a combination of the Axcelerator standard SRAM circuits and an error detection and correction (EDAC) IP core. The core is accessed via the Actel SmartGen Macro Builder software and implements a class of linear block codes called shortened Hamming. The SRAM/EDAC core combination greatly mitigates the effects of soft errors. Error rates are better than 10-10 errors/bit-day.

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