Biomedical Engineering Reference
In-Depth Information
constraints on droplet manipulations introduced by the mapping of pins to
electrodes. Different mappings for a pin-constrained chip lead to different
untestable functional units, and thereby different levels of chip testability.
For example, the untestable functional unit shown in Figure 5.2 can be made
testable by connecting electrode E4 to a different control pin (e.g., Pin 15).
Therefore, we can conclude that the key to increasing functional testability
is to generate a test-friendly pin assignment that results in a small number of
untestable functional units. To do this, test procedures must be considered
early during chip design.
5.2 Testability-Aware Pin-Constrained Chip Design
In this section, we present a DFT solution to the functional testability prob-
lem described in Section 5.1.
5.2.1 Design Method
The key idea is to incorporate fluidic operations required by the functional
test into the fluidic manipulation steps for the bioassay. Since these test-aware
fluidic manipulation steps are provided as input to a pin-assignment design
method, the resulting test-aware pin-constrained chip design guarantees a
test-friendly pin assignment that supports all the fluidic operations required
for the functional test, thereby ensuring full testability.
The pin assignment in the proposed test-aware design method is based
on the broadcast-addressing pin-constrained chip design technique pre-
sented in Chapter 3, Section 3.3. In this design method, fluidic manipulation
steps in a target bioassay, represented by the droplet schedule and droplet-
routing steps, are stored in the electronic controller in the form of electrode-
activation sequences. Each bit of the sequence represents the status of an
electrode at a specific time step. The status can be either “1” (activate), “0”
(deactivate), or “X” (don't-care), which can be mapped to either “1” or “0.” For
each electrode on the chip, its activation sequence can be represented using
the preceding three values. Each sequence can contain several don't-care
terms, which can be replaced by “1” or “0.” By careful replacement of these
don't-care terms, multiple activation sequences can be made identical.
Therefore, the corresponding electrodes can be connected to a single control
pin. The broadcast-addressing method achieves a significant reduction in the
number of control pins, and the resulting pin assignment ensures the correct
execution of all fluidic operations in the bioassay.
We first consider the functional test procedure as a separate bioassay. The
fluidic operations required by the test procedure are derived from the sched-
uling and routing steps related to the test droplets. Next, we merge these
