Problem 13.8 - Bode Plot for an Underdamped Second-Order RLC Circuit
*
* An underdamped circuit has complex poles in the s-plane. The s-plane
* magnitude of the poles is the length of a line from the origin to
* the pole and is always the undamped natural frequency. This means
* that no matter what the damping ratio of an underdamped circuit may
* be, the straight line (approximate) Bode plot always has the same
* shape. You must know something about the damping ratio or Q of the
* circuit to be able to properly interpret the approximate Bode plot.
*
* For this circuit, calculate resistance values to produce damping
* ratios of .1, .3, .5, and .707. Use the .STEP command in the LIST
* mode and an .AC sweep to obtain PROBE graphs of the output voltage
* magnitude and phase as a function of frequency for each value of
* resistance. Show all four graphs on one page.
*
* Follow the instructions in the problem statement to construct the
* approximate Bode plot. Observe the shape of the actual curves and
* relate them to the curves of Figure 13.42a in the textbook. Also
* relate the shape of the angle curves versus damping ratio to Figure
* 13.42b in the textbook.
*
.OPT NOPAGE NOBIAS
V1 1 0 AC 100
R1 1 2 RVAR 1
L1 2 3 25.33M
C1 3 0 10N
.MODEL RVAR RES(R=318.3)
.AC DEC 40 100 1E6
.STEP RES RVAR(R) LIST ???? ???? ???? ???? ; Enter the calculated
; values of resistance
; for damping ratios of .1, .3, .5, and .707.
.PROBE V(3)
.END