Pin-Constrained Chip Design - Digital Microfluidic Biochips - page 43

3
Pin-Constra ined Chip Design
In this chapter, we present three design automation techniques for pin-
constrained biochips. In contrast to the direct-addressing scheme that has
mostly been studied thus far in the literature [14-18,51-53], we assign a small
number of independent control pins to a large number of electrodes in the
biochip, thereby reducing design complexity and product cost.
3.1 Droplet-Trace-Based Array-Partitioning Method
We first present an array-partitioning-based pin-constrained design method
[57]. The design procedure relies on a droplet-trace-based array-partitioning
scheme and an efficient pin-assignment technique, referred to as the
“Connect-5 algorithm.” The proposed method is evaluated using a set of
multiplexed bioassays.
3.1.1 impact of Droplet interference and electrode-Addressing Problem
In this subsection, we formulate the pin-constraint problem for a two-
dimensional (2-D) electrode array. The goal is to use a limited number of
independent control pins to control the electrodes of a digital microfluidic
array. However, the sharing of control pins leads to the problem of droplet
interference, which is defined as the inadvertent activation of multiple elec-
trodes on which droplets are incident at any time instant. Droplet interfer-
ence results in unintentional droplet operations caused by the simultaneous
activation or deactivation of electrodes that are controlled by the same pin.
3.1.1.1 Impact of Droplet Interference
A pin-constrained layout may result in unintentional droplet movement
when multiple droplets are present in the array. Figure 3.1 shows a 4 × 4 array
in which the 16 electrodes are controlled by only 9 input pins. The pin num-
bers are indicated in the figure. Droplet interference occurs if we attempt to
move droplet D i while keeping droplet D j at its current location. Suppose D i
is at coordinate location (0,0), and D j is at coordinate location (3,2). To move
D i to (1,0), we need to activate electrode (1,0) and deactivate (0,0). This implies
43