Let's use LTspice - Create original waveforms with "behavioral voltage source"!

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Previous articleLet 's use LTspice-Frequency analysis using "FFT"! So, I explained FFT analysis using Behavioral Voltage Sources (BV) and "a circuit (adder) that combines three types of voltage sources" as the theme. This time, I will introduce how to use the Behavior Voltage Source (BV).

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What can a behavioral voltage source do?

By using a behavioral voltage source, it is possible to incorporate functions and arithmetic operators that can be used in Excel and scientific calculators into the signal source. It can also be combined with multiple voltage and current sources to model adders and complex signals.

For available functions and arithmetic operators, please refer to "B. Arbitrary behavioral voltage or current sources." from LTspice [Help Topics].

Instructions for use

We will explain how to use the behavioral power supply by taking "a signal that combines a pulse waveform and a sine wave" as an example.

First select "bv" in the "Select Component Symbole" dialog Box.

Article header library 129181 pic01 1 — Figure 1: Select "bv" in the parts dialog Box

Next, type the expression directly where "V=F(...)" is written.
Move the cursor to the component (B1) and right-click, or right-click on the character "V=F(...)" to open the editor, so use functions and operators at "Value" Write an expression.

Article header library 129181 pic02 1 — Figure 2: Enter an arbitrary expression in the "Value" field of the behavioral voltage source

This time, write "V = 0.5*SIN( 2*pi*1k*time) + V(IN)".

This formula is "a waveform obtained by adding a sine wave with a frequency of 1 kHz and an amplitude of 0.5 Vp-p and a PUSLE waveform created by an independent voltage source with the '+' operator", and the result is as shown in Fig. 3. increase.

Article header library 129181 pic03 1 — Figure 3: Behavioral voltage source realizes composite waveform of pulse and sine waves

In this way, behavioral voltage sources can create arbitrary signals because they can use functions and operators.
In addition, if you set "V = 5" in the formula, a voltage of DC 5V will be output in the same way as an independent voltage source.

Article header library 129181 pic04 1 — Figure 4: DC voltage source at "V=5"

Let's make a white noise signal!

A behavioral voltage source can use a variety of functions. Here we use the white(x) function to generate a pseudo-noise signal
is generated.

On the explanation page of the Help menu, the explanation of the white(x) function is as follows.
"Random number between -.5 and .5smoothly transitions between values even more smoothly than random()."

Interpreted, "A random number is obtained between 0.5V and -0.5V (that is, the amplitude is 1Vp-p), and it is a function that generates random numbers more smoothly than the rand() function."

As soon as possible, I'll check it out in a simulation.

Note that x in white(x) is written as "2*pi()*f*time". f is the generated frequency of the signal. Here, we set f=100kHz. The schematic and simulation waveforms are shown in Figure 5.

Article header library 129181 pic05 1 — Figure 5: white(x) function

A possible application is to generate a pseudo noise signal using the white function and perform transient analysis (time axis analysis) to verify the filter circuit.

LTspice demo file verified this time

SimulationFile__1.zip

The two simulation files that were performed this time are stored. Please try!

At the end

This time, I introduced how to create an original waveform using a behavioral voltage source!

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