Information Technology Reference
In-Depth Information
Fig
ure 4.13
Dynamic behavior of the RS latch. The top two curves are the reset and
set inputs, respectively. The bottom two curves are the complementary outputs. The
initial behavior shows the system settling into a steady state.
but then
B
rises back up to the appropriate high level. Therefore, as expected,
both long and short pulses effectively set and reset the latch.
Connections: Analysis of a Ring Oscillator
A ring oscillator is another useful test circuit, especially because the correct
behavior of the circuit is highly sensitive to the device physics of its components.
The oscillator consists of three inverters connected in a series loop without any
external drive (Figure 4.14). The simulation results in Figure 4.15 depict the
expected oscillation in signal concentrations, as well as a phase shift between the
values (values shown are protein concentrations, not mRNA). Note, however,
that oscillation occurs close to the low end of the signal values. This results
from the skewed transfer curve that describes the steady-state characteristics of
the inverters. Basically, for each inverter in the circuit, a low level of the input
[
A
]
[
B
]
Figure 4.14
Dynamic behavior of
a ring oscillator. The three curves
are the outputs of the three inverters.
Note the 120
◦
phase shift between
successive stages.
[
C
]
time (x100 sec)
