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924 ⏐⏐⏐ RESONANCE
FIG. 20.43
Resonance curve for the current of the circuit of Fig. 20.42.
icon, and with a right click of the mouse move the right cursor as close
to 7.07 mA as possible (0.707 of the peak value to define the bandwidth)
to obtain A1 with a frequency of 3.02 kHz at a level of 7.01 mA—
the best we can do with the 10,000 data points per decade. Now do a
left click, and place the left cursor as close to the same level as possible.
The result is 2.8 kHz at a level of 7.07 mA for A2. The cursors
were set in the order above to obtain a positive answer for the difference
of the two as appearing in the third line of the Probe Cursor box. The
resulting 214.22 Hz is an excellent match with the calculated value of
212 Hz.
Parallel Resonance Let us now investigate the parallel resonant circuit
of Fig. 20.33 and compare the results with the longhand solution.
The network appears in Fig. 20.44 using ISRC as the ac source voltage.
Under the Property Editor heading, the following values were set:
DC � 0A,AC � 2 mA, and TRAN � 0. Under Display, Do Not
Display was selected for both DC and TRAN since they do not play a
part in our analysis. In the Simulation Settings dialog box, AC Sweep/
Noise was selected, and the Start Frequency was selected as 10 kHz
since we know that it will resonate near 30 kHz. The End Frequency
was chosen as 100 kHz for a first run to see the results. The Points/
Decade was set at 10,000 to ensure a good number of data points for
the peaking region. After simulation, Trace-Add Trace-V(C:1)-OK
resulted in the plot of Fig. 20.45 with a resonant frequency near 30 kHz.
The selected range appears to be a good one, but the initial plot needed
more grid lines on the x-axis, so Plot-Axis Settings-X-Grid-unenable
Automatic-Spacing-Log-0.1-OK was used to obtain a grid line at 10-kHz
intervals. Next the Toggle cursor pad was selected and a left-click
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