LTspice Lesson 4e: Generate Waveforms used in Electric Circuits: EXPonential

LTspice provide a built in exponential waveform generator. This can be very helpful to generate arbitrary exponential pulses to simulate special systems such as surge protector or ESD modeling. In this lesson, we will understand all the parameters that are involved to setup such a waveform. There are some undocumented commands that can useful when a burst of signal need to be created.

Screen Shot 2019-12-10 at 5.38.20 PM.png

Equations to generate the exponential are given below, note variables are matched to above dialog box:

For t < Rise Delay:

Vinital+(Vpulse-Vinital)*(1-exp(-(time_Rise_Delay)/Rise_Tau))

For t < Fall Delay:

Vinital+(Vpulse-Vinital)*(1-exp(-(time*Rise_Delay)/Rise_Tau))-(Vpulse-Vinital)*(1-exp(-(time-Fall_Delay)/Fall_Tau))

An illustrated version is shown in following plot corrospoding : 
EXP(Vinital Vpulse Rise_Delay Rise_Tau Fall_Delay Fall_Tau) => EXP(0 1 1ms 1ms 10ms 2ms):Screen Shot 2019-12-16 at 10.26.33 AM.png

A hidden or undocumented feature of this command is to have multiple pulses in a burst fashion as it can help simulate the burst of exponential pulses in a specified period of time.

EXP(Vinital Vpulse Rise_Delay Rise_Tau Fall_Delay Fall_Tau Tpulse Npulse Tburst)

This is illustrated below:

EXP(0 1 1ms 1ms 10ms 2ms 30ms 5 200ms)

Screen Shot 2019-12-16 at 10.44.30 AM.png

In conclusion, the goal of this post is to show how to exponential can be created using the LTspice source EXP command. With some undocumented features, exponential bursts of different period and cycles can be created. This could be useful to model surges and ESD events.

 

 

 

 

 

About ExploreSilicon

My name is Kashif. I live in the heart of silicon valley and have been living here for a very long time. My passion is engineering, technology and traveling. My email is kashifjavaid@hotmail.com. Please feel free to contact if you have any suggestion or comments on any of my posts.
This entry was posted in LTspice for EE students. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s