boylistad

1084 ⏐⏐⏐ DECIBELS, FILTERS, AND BODE PLOTS
dB
Let us now concentrate on the range from 10 kHz to 1 MHz where
most of the filtering action is taking place. That was the advantage of
choosing such a wide range of frequencies when the Simulation Settings
were set up. The data have been established for the broad range of
frequencies, and you can simply select a band of interest once the
region of most activity is defined. If the frequency range were too narrow
in the original simulation, another simulation would have to be
defined. Select Plot-Axis Settings-X Axis-User Defined-10kHz to
1MEGHz-OK to obtain the plot at the bottom of Fig. 23.97. A dB plot
of the results can also be displayed in the same figure by selecting Plot-
Add Plot to Window-Trace-Add Trace-DB(V(RL:1))-OK, resulting
in the plot at the top of the figure. Using our left-click cursor option and
the Cursor Trough key, we find that the minimum is at �83.48 dB at
a frequency of 200 kHz, which is an excellent characteristic for a bandstop
filter. Using the right-click cursor and setting it on 600 kHz, we
find that the drop is �30.11 �dB or essentially 0 dB, which is excellent
for the pass-band region.
FIG. 23.97
dB and magnitude plot for the voltage across R L of the network of Fig. 23.95.