# Ltspice noise

## How do you simulate voltage noise with LTSpice?

Yes, you can inject noise using the arbitrary voltage (or current) source, then use things like the or function to create some noise.

Here is an example circuit (I separated the noise from the signal just to make things clearer - obviously you can combine them together in one function if you wish):

Simulation:

All the functions are detailed in the help under .

Noise simulation mode

Also, just in case you were not aware, SPICE has a noise simulation mode, to quote from the help files:

Basic example:

Simulation:

The above is rather boring as it only models the resistor noise (I stepped the resistor through various values to show how the Johnson noise increases with resistance). But it can be very useful with more complex circuits containing diodes/transistors/opamps/etc.

\\$\endgroup\\$Sours: https://electronics.stackexchange.com/questions/55233/how-do-you-simulate-voltage-noise-with-ltspice

## How do you simulate voltage noise with LTSpice?

Yes, you can inject noise using the arbitrary voltage (or current) source, then use things like the or function to create some noise.

Here is an example circuit (I separated the noise from the signal just to make things clearer - obviously you can combine them together in one function if you wish):

Simulation:

All the functions are detailed in the help under .

Noise simulation mode

Also, just in case you were not aware, SPICE has a noise simulation mode, to quote from the help files:

Basic example:

Simulation:

The above is rather boring as it only models the resistor noise (I stepped the resistor through various values to show how the Johnson noise increases with resistance). But it can be very useful with more complex circuits containing diodes/transistors/opamps/etc.

(Not enough rep. yet to create a comment on Oli's post, so this goes in a post of it own).

Oli's post above is very useful, but for the LTSpice beginner, it is perhaps worth explaining how to actually create of one of those "arbitrary behavioral voltage source" : I was naively expecting to be able to modify the value of a normal voltage source to enter the white(...) formula, but of course, it does not work.

Instead, you have to press the "component" button in the toolbar, and in the window that opens, pick a component of type "bv".

SPICE ( I can't tell you if LTSPice is a subset of normal SPICE or not) normally has the ability to model the noise that each device generates. I think your question is more about how to you measure how effective your filtering is and how much an external interfering signal may affect each node.

To do that what you need to do that is .AC analysis of the circuit.

To do a noise analysis you need to use both .ac and .noise. So noise analysis is a subset of ac analysis.

Sours: https://newbedev.com/how-do-you-simulate-voltage-noise-with-ltspice

## LTspice-Noise Analysis(.noise)

In this article, we will explain in detail the noise analysis(.nose) method in LTspice.

Noise analysis analyzes the noise frequency characteristics of electronic circuit.

For the types of analysis, please see the following article.

TOC

### Prepare a schematic

First, prepare a schematic for noise analysis with LTspice.

Perform noise analysis using the schematic in the following article. If you have not drawn a schematic with LTspice, we recommend that you draw a schematic before analysis.

### Signal source setting

1

We have already set the signal source in the article of “How to Draw a Schematic“.

Open the “Independent Voltage Source” screen by “right-clicking” the signal source V1 of the schematic with the mouse.

2

Select “none”.
(Noise analysis can be performed even if the signal source is SINE, but it is misleading, so we recommend changing it.)

3

Confirm that “SINE (0 2 500)” described near the signal source V1 has disappeared.

### Noise Analysis(.noise) Setting

1

Click “Simulate”-“Edit Simulation Cmd” in the menu bar to open the “Edit Simulation Command” screen.

2

Select “Noise” and enter Output: V (OUTPUT), Input: V1, Type of sweep: Decade, Number of points per decade: 100, Start Frequency: 1, Stop Frequency: 10k. You should now see “.noise V (OUTPUT) V1 dec 100 1 10k” at the bottom of the screen.

Now set V (OUTPUT) where the noise is to be checked, input signal as the signal source V1, every 10 times the frequency (Decade), at 100 points to analyze, and perform noise analysis from 1Hz to 10kHz.

In addition, LTspice can use auxiliary units as shown in the following table.

Of course, it does not matter if you enter “10000” instead of “10k” input in stop frequency without using auxiliary units.

Auxiliary unit of LTspice

3

As “.noise V(OUTPUT) V1 dec 100 1 10k” of dot command appear, place it at an appropriate position. In this article, it was placed near source V1.

Dot command can be created with Edit Text on the Schematic

Although the “.noise” of dot command was created from the screen of “Edit Simulation Command”, it can also be created by “Edit Text on the Schematic”.

Click “SPICE Directive” on the toolbar to display “Edit Text on the Schematic” screen.

Make sure that the “SPICE directive” is selected, enter the dot command syntax (“.noise V(OUTPUT) V1 dec 100 1 10k” in this case), and click OK to place the created dot command.

### Simulation

1

Click “Run” on the toolbar to run the simulation. The simulation time varies depending on the size of the circuit.

### Analysis result

In this article, we would like to easily check the analysis results with the LTspice voltage probe.

1

After simulation, when you move the cursor close to the schematic wiring, the cursor changes to “voltage probe”.

Click “OUTPUT” with the voltage probe.

2

The noise waveforms of OUTPUT appear on the graph pane.

3

You can see the frequency characteristics of the noise on the output of the op-amp.

Sours: https://spiceman.net/ltspice-noise-analysis/
LTspice tutorial - Ep6 Basics of FFT analysis and .four statment

## LTspice: Integrating Noise Over a Bandwidth

by Gabino Alonso

LTspice can perform .noise analysis of a circuit, where the noise voltage density (V/√Hz) for 1Hz bandwidth) can easily be plotted for the output noise, input noise or for any noisy component like a resistor, diode or transistor. However, you can also easily integrate noise over a selected bandwidth in a .noise analysis.

To use this feature, Ctrl-click the data trace label, V(noise), in the waveform viewer—the total RMS noise based on the bandwidth specified in the .noise directive is displayed.

If you prefer to calculate the total noise over a limited bandwidth rather than the bandwidth specified in the .noise directive you can modify the left (low) and right (high) frequency limits of the waveform viewer by clicking on the horizontal axis. Once you have your waveform displaying the bandwidth of interest, Ctrl-click the data trace label to display the total RMS noise based in the bandwidth of interest.

Alternately, you can add a .measure statement to your schematic that will calculate the total noise over a particular bandwidth, and view your results in the LTspice error log (Ctrl + L) after each simulation. (More information on using .measure statement can be found in LTspice Help (F1).

### Author

Gabino Alonso

Gabino Alonso is currently the director of strategic marketing for the Power by Linear™ Group. Prior to joining ADI, Gabino held various positions in marketing, engineering, operations, and education at Linear Technology, Texas Instruments, and California Polytechnic State University. He holds a Master of Science degree in electrical and computer engineering from University of California, Santa Barbara.

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Sours: https://www.analog.com/en/technical-articles/ltspice-integrating-noise-over-a-bandwidth.html

## Noise ltspice

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LTspice tutorial - Ep6 Basics of FFT analysis and .four statment

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