LTSPICE signal+noise simulation

Hi Er7,

I can generate a time-varying noise like transient waveform. But, for some reason LTspice random or White generator returns the exact same number for a given integer (which is odd). That means multiple runs of the circuit give exactly the same time domain signature.

Hope this works for you.

Read up on "arbitrary behavioral voltage" within the LTspice help.

I pulled the generator "bv" under the Component menu and edited its voltage statement.

V=0.111*(rand(1e8*time)-0.5)

The -0.5 is to center the waveform because rand creates a number between 0, and 1.

The 1e8 is to make sure for most time domain runs, you get a number above 1 that has a varying integer as rand only looks at the integer portion of the argument.

The 0.111 multiplier is to get you close to the 80mVpp you had requested based on trial and error.

Here is the LTspice file for your reference:

1727.White noise LTspice 5_22_19.zip

Regards,

Hooman

Hello,

I would use the factor 80m to get 80mVpp.

V=80m*(rand(1e8*time)-0.5)

I also would specify a maximum time step equal or less to 1/1e8.

.tran 0 10m 0 0.25e-8

If the noise is for audio, it's not necessary to use the factor 1e8. A factor of 1e6 in the noise-formula maybe sufficient.

Vpp/Vrms of this noise-source is about 4.
One will get a factor >6 by adding the noise voltage of 3 of these noise sources.
V=rand(1e8*time) has a first notch in the FFT at 1e8Hz.

Best regards,
Helmut

4118.White noise LTspice 3.zip