User Guide

Noise analysis
247
Figure 63 shows Probe traces for Q1’s constituent noise
sources as well as total nose for the circuit after
simulating. Notice that the trace for RMSSUM (at the top
of the plot), which is a macro for the trace expression
SQRT(NTOT(Q1) + NTOT(Q2) + NTOT(Q3) + ... ),
exactly matches the total output noise, V(ONOISE),
calculated by PSpice.
Figure 62 Device and total noise traces for EXAMPLE.DSN.
Frequency is swept from 100 kHz to 10 GHz by decades,
with 10 points per decade. The V1 independent voltage
source is the only input to an amplifier, so it is the only AC
stimulus to this circuit. Magnitude equals 1 V and relative
phase is left at zero degrees (the default). All other voltage
sources have zero AC value.
To
f
in
d
out more a
b
out PSpice macros,
refer to PSpice A/D online Help.
Note T
h
e source, V1, is a VSIN source t
h
at
is normally used for setting up sine wave
signals for a transient analysis. It also has
an AC property so that you can use it for an
AC analysis.
To find out more about VSIN and other
source symbols that you can use for AC
analysis, see Using time-based
stimulus parts with AC and DC
properties on page 3-77.
Pspug.book Page 247 Wednesday, November 11, 1998 1:14 PM