[SI-LIST] Re: FPGA SI Issues in Space Applications

Sammit,

You've received great advices from the forum. Here are my suggestions to add 
to the others:

1. Ask Xilinx's applications group about radiation hardness info and 
suggestions. I have seen them on the company's web site. The company may 
have rad-hard FPGAs you can use. Those would have built-in radiation 
hardened flip flops and SRAM cells but they will be more expensive because 
of the increased die sizes.
2. Use a good logic design practice to reduce the impact of 
radiation-induced upset events: all state machines should have all illegal 
states lead to either known states or the reset state at the next cycle. The 
drawback is that it will increase the sizes and complexity of the state 
machines.

Khanh



----- Original Message ----- 
From: <HaroldLSJ@xxxxxxx>
To: <si-list@xxxxxxxxxxxxx>; <sammit.adhya@xxxxxxxxxxxx>
Sent: Wednesday, April 26, 2006 1:09 PM
Subject: [SI-LIST] Re: FPGA SI Issues in Space Applications


>
> Sammit,
>
> The following is unclassified.  Here is some of the radiation data I  have 
> on
> Xilinx SRAM FPGA devices.  Multiple XC4036XL-1HQ240C and 
> XC4036XLA-09HQ240C
> were configured in a 40 MHz FIFO that occupied about 90% of  the FPGA 
> CLBs.
> Both devices are 3.3V.  Irradiation was provided by a  high energy 
> Cobalt-60
> source.  The dose rate was determined using a Fricke  (ferrous sulfate)
> dosimeter and was corrected for silicon material absorbed  dose.  An 
> aluminum shield
> with an open beam aperture to the FPGA was  used to reduce low energy
> bremsstrahlung photons produced by electrons  scattering off the lead 
> shielding.  The
> dose rate was about 0.47 krad per  hour.  The power supply current for the
> XC4036XL devices began rising at  about 40 krad cumulative dose and the 
> current
> had doubled by 70 krad cumulative  dose.  The power supply current for the
> XC4036XLA devices began rising at  about 20 krad cumulative dose and the 
> current
> had doubled by 25 krad  cumulative dose and continued to rise to 6X
> pre-radiation levels.  The  increased current is due to leakage currents. 
> Annealing the
> device for  150+ hours at 50 °C will lower the leakage current by about 
> 1/3 for
> the  XC4036XL, but current will rise again on radiation exposure.  The 
> first
> errors were detected at about 57 krad cumulative dose for the XC4036XL and
> much  sooner for the XLA device.  The total number of errors per device
> approached about 2,000 for the XC4036XL.  There was no evidence of 
> increased signal
> skew or a change in rise time of the output signals.   Most all of the 
> errors
> were soft and could be cleared with an  active circuit reset but some 
> errors
> required power down and  reconfiguration of the XC4036XL.  However, the 
> XLA
> devices could not be  reliably reconfigured after a power down reset.  I 
> would
> recommend an  external watch-dog and reconfiguration circuit.
>
> My Regards,
>
> Harold L. Snyder, Jr.
> Scientist & Consultant
>
>
> Begin Included Message Dated 4/26/2006 1:25:31 PM Central Daylight Time,
> lfresearch@xxxxxxx writes:
> =======================================
> Just to  add to the mix..
>
> The philosophy of designing circuits to withstand  partical effects is a
> tricky subject to discuss openly, it may even have  restrictions.
>
> Needless to say, considder the effect on a semiconductor  when high
> energy particals arrive in the lattice.
>
> The art/science  is designing a circuit such that the effects first are
> not catostrophic:  second, that over time with irradiation does not
> change the circuit  characteristics.
>
> More than this.... you will need more specialised  help
>
> Chris Padilla (cpad) wrote on 4/26/2006, 12:59 PM:
>
>> You  are basically asking about immunity requirements for the chips.   To
>> put it simply, you need to protect the ICs by placing them in a  sealed
>> metal box.  Naturally, the devil is in the  details!!
>>
>> How do you plan to test this product to this  environment?  Back in my
>> days at NASA-Ames, we used to take  semi-conductor arrays to the
>> cyclotron located at the University of  California, Davis, and fire
>> particles at the arrays to simulate sun  bursts and cosmic waves and
>> such.=20
>>
>> You can also take  such products to any EMC lab and have them do radiated
>> immunity  tests.  Basically they just bombard your product with RF energy
>>  and see how it performs.
>>
>> Chris Padilla
>> SI  Engineer
>> Cisco Systems
>> San Jose, CA
>>
>>  -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx  [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Sammit  Adhya
>> Sent: Wednesday, April 26, 2006 10:42 AM
>> To:  si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: FPGA SI Issues in Space  Applications
>>
>> Our area of research is unique in the sense that  we're using SRAM based
>> FPGAs from Xilinx. The idea is that with  scrubbing and triple modular
>> redundancy, that should provide immunity  for SEUs and latchup's. That
>> has already been done, so we're working  on basically the ability to
>> dynamically move around different  reconfigurable modules in the case of
>> failures. In theory, until you  have hit the device with the maximum
>> ionizing dose, the devices should  not fail.
>>
>> I guess I just don't have a good understanding of  how SI issues affect
>> signals within the FPGA and what are the common  practices used to
>> prevent these issues when writing HDL. The harsh  space environment I
>> would think adds to this issues and I haven't seen  much on trying to
>> inherently protect the hardware.  Thanks!
>>
>> Sincerely,
>> Sammit Adhya
>>
>> On  4/26/06, Tom Biggs <tbiggs@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> >  Assuming you are talking about satellites and not launchers, one 
>> > issue
>>
>> > to consider is that long term radiation affects  transister=20
>> > characteristics. So you can't trust specs such as  Vil, Vih, Vol,
>> Voh,=20
>> > rise times, propogation  delays.
>> >
>> > So how do you design? You understand what  the affects are, and you=20
>> > adjust the numbers for the worst case  over the lifetime of the=20
>> > satellite. Lots of extra margin in  the design is highly recommended.
>> >
>> > I'm glad to see  that you've addressed the SEU issue. A flip-flop
>> that=20
>> >  decides to change state randomly is difficult to design around. It
>>  is=20
>> > even harder when the flip-flop is controlling the  configuration of the
>>
>> > FPGA. How are you dealing with  radiation induced latch-up?
>> >
>> > Using non-radiation  hardened electronics in space is tricky.
>> > There was once a  Japanese satellite that used seven 
>> > microprocessors.=20
>> > The  processors were not radiation hardened, but they didn't worry=20
>> >  because of all of the redundancy. If one or two get a radiation 
>> > hit,=20
>> > the others take over and reset the crashed cpus. Then  along came a=20
>> > strong solar flare and knocked out all seven at  once. End of
>> satellite.
>> >
>> >     -tom
>> >
>> > -----Original Message-----
>> > From:  si-list-bounce@xxxxxxxxxxxxx=20
>> >  [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> > On Behalf Of Sammit  Adhya
>> > Sent: Tuesday, April 25, 2006 11:21 PM
>> > To:  si-list@xxxxxxxxxxxxx
>> > Subject: [SI-LIST] FPGA SI Issues in Space  Applications
>> >
>> >
>> > Hello All,
>>  >
>> > This is my first time posting to the list so hopefully the  question=20
>> > isn't too generic. I'm currently working on a  research project to
>> use=20
>> > FPGAs as flight computers in  space at the University of Colorado. I=20
>> > was wondering if people  had any general advice for designing
>> circuits=20
>> > in space  with it comes to signal integrity and high radiation
>>  environments.
>> >
>> > Things like single event upsets have  already been addressed, but I was
>>
>> > looking for some  insight issues beyond SEUs, SETs and SEEs. Any=20
>> > specific ways  of routing circuits or designing them to inherently=20
>> > protect  them the harsh space environment? Thanks!
>> >
>> > --
>>  > Sincerely,
>> > Sammit Adhya
>> >  ------------------------------------------------------------------
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>
> -- 
> Cheers,
> Derek  Walton
> L F Research
> Poplar Grove, IL 61065,  USA
>
>
>
> =======================================
> End Included Message.
>
>
>
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