Introduction to LTspice

6.101 Spring 2014 Lecture 4

SPICE

• Simulation Program with Integrated Circuit Emphasis

• Developed in 1973 by Laurence Nagel at UC Berkeley’s Electronics Research Laboratory

• Dependent on user defined device models

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Netlists

6.101 Spring 2014 Lecture 4

Components

Commands

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LTspice

• Developed in 1998 by Mike Engelhardt at Linear Technology Corporation

• GUI, simulator, and schematic -> netlist for SPICE • FREE and comes with tons of models

6.101 Spring 2014 Lecture 4

You do this Ltspice makes this

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Getting Started

6.101 Spring 2014 Lecture 4

THAT’S IT!

These buttons are where you will live

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Component to Menu Item Matchup

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Net Labels

6.101 Spring 2014 Lecture 4

By labeling nets you can avoid a giant mess of wires. Always use these for at least your power supplies. When you start making large circuits, your power supplies will provide energy all over your schematic.

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Adding Other Components

6.101 Spring 2014 Lecture 4

Devices besides basic resistors, capacitors, and inductors are found from this button

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Op-Amps

6.101 Spring 2014 Lecture 4

There are no “ideal” op-amps in LTspice. BUT, you can select from any of Linear Tech’s… which (in some cases) are close.

(LT1022 is my “go-to”)

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Editing Components

6.101 Spring 2014 Lecture 4

Just right click the component

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Editing Components

6.101 Spring 2014 Lecture 4

This is the basic voltage source menu. Use this for DC sources such as power supplies or bias voltages.

But what about this?

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Editing Components

6.101 Spring 2014 Lecture 4

Voltage sources can produce many test signals. PWL can be used to construct any signal.

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Selecting Device Model

6.101 Spring 2014 Lecture 4

There are no “ideal” BJT’s, MOSFET’s, Diode’s, etc. You must select a model (provided by LTspice).

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Simulation: Transient Transient simulation gives Voltage and/or Current

vs.time.

6.101 Spring 2014 Lecture 4

These are transient parameters for a voltage source

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Simulation: Transient

6.101 Spring 2014 Lecture 4

This is all you really need

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Random Tangent: Parameters

6.101 Spring 2014 Lecture 4

This is a parameter

You MUST define all of your parameters. The “list” command allows you to choose multiple values (simulation simulates each value separately).

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What Should My Circuit Do?

• The very first step to any simulation is to know how your circuit should behave. Simulation is a verification tool NOT A CIRCUIT SOLVER.

• So how should this circuit behave?

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Here’s Where You Write the Solution

6.101 Spring 2014 Lecture 4

vx vo

i1

i2

i3

A DOUBLE POLE!!

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Expected Behavior

• Double pole is at:

• We expect frequencies up to this point to be large, but frequencies above to quickly drop off due to the -40 dB/decade characteristic of the double pole

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Transient Simulation

6.101 Spring 2014 Lecture 4

Hover over the desired voltage node to be probed and click when you see this symbol

**This is the current probe

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Transient Simulation

6.101 Spring 2014 Lecture 4

1 kHz

10 kHz

100 kHz

1 MHz

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AC Simulation

6.101 Spring 2014 Lecture 4

This is the AC parameter. Just set the amplitude to 1

AC simulation gives Voltage and/or Current vs.frequency.

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AC Simulation

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Extra Fun: Math in LTspice

6.101 Spring 2014 Lecture 4

Remember:

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Transient Simulation

6.101 Spring 2014 Lecture 4

It’s the same as before!

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Even More Fun

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AC Simulation

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Making Things Pretty

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Making Things Pretty

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Questions??

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