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ƒ r
27.051 kHz. Clearly, therefore, the frequency at which the phase angle
is zero and the total impedance appears resistive is less than the frequency
at which the output voltage is a maximum.
Electronics Workbench
The results of Example 20.9 will now be confirmed using Electronics
Workbench. The network of Fig. 20.36 will appear as shown in Fig.
20.47 after all the elements have been placed as described in earlier
chapters. In particular, note that the frequency assigned to the 2-mA ac
current source is 100 kHz. Since we have some idea that the resonant
frequency is a few hundred kilohertz, it seemed appropriate that the
starting frequency for the plot begin at 100 kHz and extend to 1 MHz.
Also, be sure that the AC Magnitude is set to 2 mA in the Analysis
Setup within the AC Current dialog box.
FIG. 20.47
Using Electronics Workbench to confirm the results of Example 20.9.
For simulation, the sequence Simulate-Analyses-AC Analysis is
first selected to obtain the AC Analysis dialog box. The Start frequency
is set at 100 kHz, and the Stop frequency at 1 MHz; Sweep
type is Decade; Number of points per decade is 1000; and the Vertical
scale is Linear. Under Output variables, node number 1 is selected
as a Variable for analysis followed by Simulate to run the program.
The results are the magnitude and phase plots of Fig. 20.48. Starting
with the Voltage plot, the Show/Hide Grid key, Show/Hide Legend
key, and Show/Hide Cursors key are selected. You will immediately
note under the AC Analysis cursor box that the maximum value is
95.24 V and the minimum value is 6.94 V. By moving the cursor until
we reach 95.24 V (y1), the resonant frequency can be found. As shown
COMPUTER ANALYSIS ⏐⏐⏐ 927