Hardware Reference
In-Depth Information
Fig. 2.7
Pseudocode for determining the recovery operation for
opt
i
!
[
i Do
1
;o
2
;:::o
k
P
r
W
O
{
opt
i
,
opt
j
j
opt
j
2
pred
.
opt
i
/,
8
j }
For any operation
opt
i
, its set of error-recovery operations
R
i
can be derived by
the procedure presented in Fig.
2.7
. According to the above discussion, for any
operation
opt
i
we can derive the set of recovery operations
R
i
.
Based on the relationship between operations in the initial sequencing graph, we
can further add edges between operations in the set
R
i
, and thus derive the error-
recovery graph G
Re
i
for
opt
i
. If an error occurs in
opt
i
, we will re-execute operations
in G
Re
i
for error-recovery.
It is important to note that some electrodes on the biochip are intentionally
left unused and reserved for storage of backup droplets. An example is shown in
Fig.
2.6
b; all electrodes on the boundary of the chip are allocated and reserved as
storage cells. Thus backup droplets can be easily transported on the biochip.
2.3.2
Reliability Consideration in Error-Recovery
When an error is detected during the execution of a bioassay, it is inefficient to
ensure reliable operations by simply re-executing the operation for which an error
occurred. This is because the errors that occur during the execution of a bioassay
usually are caused by defects involving electrodes; thus, multiple errors may occur
in the same region of the biochip at different times. Two examples are discussed
below to illustrate the errors caused by the charge-trapping phenomenon and DNA
fouling.
When the electrodes of a digital microfluidic biochip are actuated excessively,
physically-trapped charge and residual charge may lead to reliability problems [
7
,
8
].
Charge trapping is a phenomenon in which charge is trapped and concentrated in
the dielectric insulator of the biochip. The trapped charge can lead to a reduction
in the electrowetting force and malfunctions in the execution of the bioassay.
An example is shown in Fig.
2.8
a.
