PSpice Noise Analysis

Discussion in 'CAD' started by Bob Penoyer, Nov 19, 2003.

1. Bob PenoyerGuest

I'm somewhat new to PSpice. One apparent feature is Noise Analysis.
When I invoke this function, a couple of new terms appear in the left
pane of the Add Traces window in Schematic. For my particular circuit,
these are NTOT(ONOISE), NTOT(R1), NTOT(R6), V(INOISE), and V(ONOISE).

I assume INOISE is input noise and ONOISE is output noise. They appear
to give a noise profile as a function of frequency but what, exactly,
are INOISE and ONOISE? Are they used separately? Should I use their
ratio?

A key question: Is there a direct way to make PSpice calculate the
total rms voltage or current noise referenced to the input?

2. Kevin AylwardGuest

No. They are the effective input/rthz and output noise/rthz, as you
guessed.
I don't remeber much about PSpice, now but I would guess that NTOT might
be total noise;-)

Now if you were using SuperSpice, http://www.anasoft.co.uk,which is much

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.

3. qrkGuest

INOISE = equivalent noise of total circuit, referenced to the input
ONOISE = equivalent noise of total circuit, referenced to the output
NTOT = total noise, used mostly for device noise. See PSpice help for
"Device noise variables" for more noise info.

In AC analysis, you set up the input source and output node as well as
enable the noise reporting.

The answer to your "key question" is yes. INOISE and ONOISE calculate
the total circuit noise.

Mark

4. Jim ThompsonGuest

Yes, Mark, we *do* know a lot about noise ;-)

...Jim Thompson

5. Bob PenoyerGuest

Two follow-up questions:

1. Do INOISE and ONOISE include the noise effects of components listed
as arguments of NTOT? That is, if there are resistors connected in an
op-amp circuit, for example, do INOISE and ONOISE include the combined
effects of the resistors and the op-amp?
2. Is there a way to convert the spectral profiles of INOISE and
ONOISE to the total noise, that is, integrate INOISE or ONOISE over
the swept frequency spectrum?