User Guide

Noise analysis
245
Analyzing Noise in the Probe window
You can use these output variable formats to view traces
for device noise contributions and total input or output
noise at every frequency in the analysis.
To view this... Use this output variable... Which is represented by this equation*...
* To find out more about the equations that describe noise behavior, refer to the appropriate device type in the
Analog
Devices
chapter in the
OrCAD PSpice Reference Manual
.
F
licker noise for a device NFID(
device_name
)
NFIB(
device_name
)
noise
∝
Shot noise for a device NSID(
device_name
)
NSIB(
device_name
)
NSIC(
device_name
)
For diodes and BJTs:
noise ∝
For GaAsFETs, JFETs, and
MOSFETs:
noise ∝
Thermal noise for the RB, RC, RD,
RE, RG, or RS constituent of a
device, respectively
NRB(
device_name
)
NRC(
device_name
)
NRD(
device_name
)
NRE(
device_name
)
NRG(
device_name
)
NRS(
device_name
)
noise
∝
Total noise for a device NTOT(
device_name
) Sum of all contributors in
device_name
Total output noise for the circuit NTOT(ONOISE)
RMS-summed output noise for the
circuit
V(ONOISE) RMS sum of all contributors
Equivalent input noise for the
circuit
V(INOISE)
For a
b
rea
k
d
own o
f
noise output varia
bl
es
by supported device type, see Table 6
on page 13-358
.
k
f
I
a
f
f
b
-----
⋅
2 qI
4kT
Id
Vd
-------
2
3
---
⋅⋅
4kT
R
----------
NTOT device
()
device
∑
NTOT ONOISE
()()
VONOISE()
gain
---------------------------------
Pspug.book Page 245 Wednesday, November 11, 1998 1:14 PM