ltspicesimulation
I am trying to inject noise into the Voltage Source as shown in this thread. The NOISE function looks like this: V=(white(2e6*time)/10). I am new to LTSpice. How to actually use the white function? Where do I go in the LTSpice tool to enter this function?
I can right click on the voltage source and I see this window. Where do I enter the white function?
Spice models generally do not include noise in transient simulations. The "noise" model in spice is used only in AC sweeps, where the noise power is calculated as a function of frequency. While resistor (Johnson–Nyquist) noise is in the model, semiconductor models often do not have accurate noise models. The spice diode model does include flicker noise, but not other noise sources.
For your purposes, AC analysis may be sufficient assuming that your diode has a proper model, since what you want is to see if the noise power density is flat. But, I doubt that the Zener model includes accurate noise parameters. The spice model of the diode mentioned in this question (EDZV24B) does not include any noise parameters (which are the AF, KF, and FFE parameters).
Another option (for transient simulations) is to include a voltage sources controlled by a random number. For a description of using this approach to noise modeling, this website from Giorgio Vazzana has good information. But, to follow this approach, you have to know how much noise to expect. Also, the transient simulation would not normally include noise added by the transistor.
An example noise voltage source (from the above mentioned website) is:
Vn 1 n1 dc 0V ac 1mV trrandom (1 5us 0s 125m 0m)
Just use the G circuit element (voltage controlled current source) with a lookup table (LUT) specification:
Note: the capacitor C1 is there only to avoid an error because the simulator doesn't like node C to be floating.
This is the relevant section of the online help (emphasis mine):
G. Voltage Dependent Current Source Symbol Names: G, G2
There are three types of voltage dependent current-source circuit elements.
Syntax: Gxxx n+ n- nc+ nc-
This circuit element asserts an output current between the nodes n+ and n- that depends on the input voltage between nodes nc+ and nc-. This is a linearly dependent source specified solely by a constant gain.
Syntax: Gxxx n+ n- nc+ nc- table=(, , ...)
Here a lookup table is used to specify the transfer function. The table is a list of pairs of numbers. The second value of the pair is the output current when the control voltage is equal to the first value of that pair. The output is linearly interpolated when the control voltage is between specified points. If the control voltage is beyond the range of the look-up table, the output current is extrapolated as a constant current of the last point of the look-up table.
Here are the results of the simulation:
As you can see you only need to specify two points in the LUT if you just want a VCCS with an hard limiting characteristics, i.e. linear inside a given voltage range and fixed saturated limit out of that range.
Best Answer
Use the behavioral voltage source and apply the white() function there. Hit F2, then look for "bv" as the item in the dialog box. Drop that puppy down on the schematic. Do NOT use the regular voltage source for this.