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Actel Reliability Critical Design Review Robert Abiad University of California - Berkeley. Actel Overview. Overview of Actel SX-S Field Programmable Gate Array 2012 flip-flops 4024 combinatorial modules 5V I/O supply 2.5V internal supply >200 MHz performance
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Actel Reliability • Critical Design Review • Robert Abiad • University of California - Berkeley
Actel Overview • Overview of Actel SX-S • Field Programmable Gate Array • 2012 flip-flops • 4024 combinatorial modules • 5V I/O supply • 2.5V internal supply • >200 MHz performance • Output 400-500 ps rise time for commercial part • Output 2 ns low-slew fall time for commercial part
Actel Difficulties • Metastability • Violation of flip-flop setup time resulting in undefined output Solution - Add another synchronizing flip-flop
Actel Difficulties • Glitch Sensitivity • Flip-flops respond to ns glitches Solution - Sample clock input where glitches will create failures
Actel Difficulties • Power On Reset • Can cause timing violations if removed asynchronously to flip-flop inputs. Solution - Assert asynchronously, but de-assert synchronously
Actel Difficulties • Clocks • Only HCLK is absolutely guaranteed • Use as main clock • CLKA/CLKB are susceptible to too much skew • Use with caution • QCLKA/B/C/D are guaranteed in their quadrants but not outside • Use with caution • Unused clocks must be grounded.
Actel Difficulties • Timing Analysis • Must be done • Easiest when design is synchronous • Less repeatable when the part is closer to full.
Actel Difficulties • Ground Bounce • The momentary difference between the ground inside an IC and on a PCB caused by the transition of I/Os on the IC to ground. • The result of inductance between the IC ground and the PCB. • Can cause receiving flip-flops to clock. • Can temporarily increase the array voltage on Actels and destroy antifuses. • Solutions • Separate simultaneously switching I/Os • Provide the shortest path to ground as possible for parts • Use low slew outputs on Actel pins • Install resistors in series with signals that may glitch
Actel Difficulties • Power Decoupling • Best to have a mix of decoupling capacitor sizes (100nF, 10nF, 1nF) • Use short, fat traces • Utilize interplane capacitor
Actel Difficulties • Signal Integrity • Fast signals on long traces ring - use termination • Signals that travel near each other talk • Separate sensitive signals • Route traces in opposite directions on adjacent layers • Slow signals down - low slew or series termination • Keep a reference plane adjacent to signal layers • Clock edges need to be just right • Slow edges cause multiple transitions • Fast edges create noise • Stubs increase noise - don’t use on sensitive signals