Biomedical Engineering Reference
In-Depth Information
3
6
1
24
8
4
7
Pin numbers for
the electrodes
are shown inside
the squares
11
6
12
7
3
15 18 26 14
7
25 12 13 14 8 4
16
9
7
4 18
17
13
20
9
7 26 11 13 27 24 23 21 22 19
9
5
4
23
16
2
11
10
1
3
7
2
12
High voltage
12
E
4
E
4
13
14
12
13
14
12
Low voltage
E
1
E
2
E
3
E
1
E
2
E
3
Figure 5.2
An example of an untestable functional unit on a pin-constrained chip for a multiplexed assay.
large number of qualified regions for a target application, which in turn con-
tributes to increased flexibility for design and fault tolerance. A functional
unit is considered to be testable if the test-related droplets can be manipu-
lated to carry out the target fluidic operations on it. These fluidic operations
in the functional mode are always possible on a direct-addressable chip.
However, for a pin-constrained chip, due to constraints introduced by the
sharing of input control pins by electrodes, carrying out these functional-test
operations on some functional units can result in the problem of electrode
interference described in Section 3.1.
Figure 5.2 shows a pin-constrained chip design for a representative protein-
dilution assay. The functional test procedure requires a splitting operation to be
executed on the highlighted functional unit. To do this, we first activate Pin 13 to
hold a test droplet at E
2
. Next, we deactivate Pin 13, and activate Pin 12 and Pin 14
to split the test droplet into two small droplets seated on E
1
and E
3
. However, E
4
is also charged by activating Pin 12. As a result, the split droplet that is supposed
to be seated on E
3
will be moved unintentionally to the boundary of E
4
and E
3
.
Due to the preceding electrode interference problem, the functional test
cannot be applied to all the functional units in a pin-constrained chip
design. Therefore, functional testability for a pin-constrained chip is usually
less than 100%. Note that the reduction in testability is due to the conflicts
between the fluidic operation steps required by the functional test and the
