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

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Design Analog Devices

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!

The behavioral voltage source can use various functions. Here we use the white(x) function to generate a pseudo-noise signal
Let's try generating it.

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

In other words, it is a function that generates random values between 0.5V and -0.5V (i.e., the amplitude is 1Vp-p), and generates random values more smoothly than the rand() function.

Let's check it out with a simulation right away.

Note that the x in while(x) is written as "2*pi()*f*time". f is the signal generation frequency. Here, f=100kHz. The circuit diagram and simulation waveform are shown in Figure 5.

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

One possible application is to use the white function to generate pseudo-noise signals and perform transient analysis (time axis analysis) to verify filter circuits.

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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