IEEE Circuits and Systems Magazine - Q2 2021 - 65

and Schur elimination are the most time-consuming
parts. By profiling our algorithm on datasets [189],
Schur and Jacobian computations account for 29.8%
and 48.27% of total time. We implemented Schur elimination
and Jacobian updates on FGPA fabrics [156].
Compared with the CPU implementation, the FPGA
achieves 4× and 27× speedup for Schur and Jacobbian,
and saves 76% energy.
VIII. Application of FPGAs in Space Robotics
In the 1980s, field-programmable gate arrays (FPGA)
emerged as a result of increasing integration in electronics.
Before the use of FPGA, glue-logic designs
were based on individual boards with fixed components
interconnected via a shared standard bus,
which has various drawbacks, such as hindrance of
high volume data processing and higher susceptibility
to radiation-induced errors, in addition to inflexibility.
The utilization of FPGAs in space applications
began in 1992, for FPGAs offered unprecedented flexibility
and significantly reduced the design cycle and
development cost [190].
FPGAs can be categorized by the type of their programmable
interconnection switches: antifuse, SRAM,
and Flash. Each of the three technologies comes with
trade-offs. Antifuse FPGAs are non-volatile and have
minimal delay due to routing, resulting in a faster speed
and lower power consumption. The drawback is evident
as they have a relatively more complicated fabrication
process and are only one time programmable. SRAMbased
FPGAs are the most common type employed in
space missions. They are field reprogrammable and use
the standard fabrication process that foundries put in
significant effort in optimizing, resulting in a faster rate
of performance increase. However, based on SRAM,
these FPGAs are volatile and may not hold configuration
if a power glitch occurs. Also, they have more substantial
routing delay, require more power, and have a higher
susceptibility to bit errors. Flash-based FPGAs are nonvolatile
and reprogrammable, and also have low power
consumption and route delay. The major drawback is
that in-flight reconfiguration is not recommended for
flash-based FPGAs due to the potentially destructive results
if radiation effects occur during the reconfiguration
process [191]. Also, the stability of stored charge on
the floating gate is of concern: it is a function including
factors such as operating temperature, the electric fields
that might disturb the charge. As a result, flash-based
FPGAs are not as frequently used in space missions [192].
A. Radiation Tolerance for Space Computing
For electronics intended to operate in space, the harsh
space radiation present is an essential factor to conSECOND
QUARTER 2021
sider. Radiation has various effects on electronics, but
the commonly focused two are total ionizing dose effect
(TID) and single event effects (SEE). TID results from
the accumulation of ionizing radiation over time, which
causes permanent damage by creating electron-hole
pairs in the silicon dioxide layers of MOS devices.
The effect of TID is that electronics gradually degrade
in their performance parameters and eventually
fail to function. Electronics intended for application
in space are tested for the total amount of radiation,
measured in kRads, they can endure before failure.
Usually, electronics that can withstand 100 kRads are
sufficient for low earth orbit missions to use for several
years [191].
SEE occurs when high-energy particles from space
radiation strike electronics and leave behind an ionized
trail. The results are various types of SEEs [193], which
can be categorized as either soft errors, which usually
do not cause permanent damage, or hard errors, which
often cause permanent damage. Examples of soft error
include single event upset (SEU), and single event
transient (SET). In SEU, a radiation particle struck a
memory element, causing a bit flip. Noteworthy is that
as the cell density and clock rate of modern devices increases,
multiple cell upset (MCU), corruption of two
or more memory cells in a single particle strike, is increasingly
becoming a concern. A special type of SEU is
single event functional interrupt (SEFI), where the upset
leads to loss of normal function of the device by affecting
control registers or the clock. In SET, a radiation particle
passes through a sensitive node, which generates a
transient voltage pulse, causing wrong logic state at the
combinatorial logic output. Depending on whether the
impact occurs during an active clock edge or not, the
error may or may not propagate. Some examples of hard
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