Biomedical Engineering Reference
In-Depth Information
t 0
t 0
Reduced
frequency
Mismatch
Mix
Mix
t 1
t 2
Inc.
Inc.
t 3
t 3
Derived schedule
Actual timing diagram
Figure 7.2
An example of a scheduling error ( Inc. refers to incubation operation).
operation frequency, that is, the frequency of the control signals for the syn-
thesized design, exceeds the transportation speed limit of the chip. In this
case, the target-synthesized bioassay must be executed at a lower frequency.
The reduction in clock frequency leads to performance degradation for some
fluidic modules. For example, the operation time for a 2 × 3 mixer increases
from 3 s to 10 s when the operation frequency is reduced from 10 Hz to 3 Hz
(the mixing time of 3 s for 10 Hz frequency is taken from Palik et al. [49]). Some
other modules, however, are insensitive to a change in operation frequency.
An optical detector has the same detection time at all clock frequencies, and
a thermal incubator requires a fixed incubation time. These differences in
the performance degradation for different types of modules can invalidate
the scheduling results derived from the synthesis procedure. The result-
ing timing mismatch in bioassay execution is referred to as scheduling error .
Figure 7.2 shows an example of scheduling error for an assay that involves
a mixing step followed by an incubation operation. In the schedule derived
from the synthesis flow, incubation starts at time t 1 . However, when the oper-
ation frequency is reduced, mixing finishes at a later time t 2 , which leads to
a timing mismatch between the mixer and the incubator.
A scheduling error can be catastrophic for a bioassay that is mapped to
a microfluidic array. For example, for on-chip dilution, a splitting opera-
tion is scheduled right after a mixing operation. A scheduling error may
cause a splitting of a droplet that is not fully mixed, which can lead to two
droplets with different sample concentrations. The solution to this incorrect
scheduling problem requires complete resynthesis, which is inefficient and
undesirable for the end user. Therefore, research is needed to avoid it in the
synthesis procedure.
Electrode charging is also a common problem in the execution of a synthe-
sized bioassay. In a synthesis result, an electrode can be activated for an arbi-
trarily long period of time. However, in real chips, long activation duration for
an electrode may lead to charge accumulation on the electrode, and thereby
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