User Guide

Plotting hysteresis curves
267
The QSTD model is defined as:
.MODEL QSTD NPN( is=1e-16 bf=50 br=0.1 rb=50 rc=10
tf=.12ns tr=5ns
+ cje=.4pF pe=.8 me=.4 cjc=.5pF pc=.8 mc=.333 ccs=1pF
va=50)
Instead of using the DC sweep to look at the hysteresis,
use the transient analysis, (Print Step = .01ms and Final
Time = 2ms) sweeping VIN from -1.8 volts to -1.0 volts
and back down to -1.8 volts, very slowly. This has two
advantages:
• it avoids convergence problems
• it covers both the upward and downward transitions
in one analysis
After the simulation, in the Probe window in PSpice , the
X axis variable is initially set to be Time. By selecting
X Axis Settings from the Plot menu and clicking on the
Axis Variable button, you can set the X axis variable to be
V(1). Then use Add on the Trace menu to display V(7),
and change the X axis to a user defined data range from
-1.8V to -1.0V (Axis Settings on the Plot menu). This plots
the output of the Schmitt trigger against its input, which is
the desired outcome. The result looks similar to Figure 67.
Figure 66 Netlist for Schmitt trigger circuit.
*
C
ap
t
ure
N
e
tli
s
t
R_RIN 1 2 50
R_RC1 0 3 50
R_R1 3 5 185
R_R2 5 8 760
R_RC2 0 6 100
R_RE 4 8 260
R_RTH2 7 0 85
C_CLOAD 0 7 5PF
V_VEE 8 0 dc -5
V_VIN 1 0
+PWL 0 -8 1MS -1.0V 2MS -1.8V
R_RTH1 8 7 125
Q_Q1 3 2 4 QSTD
Q_Q2 6 5 4 QSTD
Q_Q3 0 6 7 QSTD
Q_Q4 0 6 7 QSTD
Pspug.book Page 267 Wednesday, November 11, 1998 1:14 PM