Introduction to LTspice

Acknowledgment: LTspice material based in part by Devon Rosner (6.101 TA 2014), Engineer, Linear Technology

6.101 Spring 2020 Lecture 4 SPICE

• Simulation Program with Emphasis • Developed in 1973 by Laurence Nagel at UC Berkeley’s Electronics Research Laboratory • Dependent on user defined device models

6.101 Spring 2020 Lecture 42 Netlists

Components

Commands

6.101 Spring 2020 Lecture 4 3 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

You do this Ltspice makes this

6.101 Spring 2020 Lecture 4 4 Getting Started

THAT’S IT!

These buttons are where you will live

6.101 Spring 2020 Lecture 4 5 Component to Menu Item Matchup

6.101 Spring 2020 Lecture 4 6 Net Labels

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.

6.101 Spring 2020 Lecture 4 7 Adding Other Components

Devices besides basic , , and are found from this button

6.101 Spring 2020 Lecture 4 8 Op-Amps

There are no “ideal” op-amps in reality. BUT, there are in LTspice.

PAY CLOSE ATTENTION TO THE TEXT

You must literally include .lib opamp.sub in your netlist or schematic as a SPICE directive.

6.101 Spring 2020 Lecture 4 9 Op-Amps Though listed as “ideal” there are still 2 parameters you can tweak.

Open Loop Gain: As this number approaches infinity, the Op Amp becomes more “ideal”. Look at some Op Amp data sheets to see some real open loop gains.

Gain Bandwidth: As this number approaches infinity, the Op Amp becomes more “ideal”. To check if this is high enough, multiply your desired Closed Loop Gain by your highest desired output frequency. 6.101 Spring 2020 Lecture 410 Op-Amps

To more accurately model a real Op Amp not available in LTspice, UniversalOpamp2 has many tweakable parameters.

Open loop gain, gain bandwidth, slew rate, current limit, rail-rail voltage, input voltage offset, phase margin, Rin, etc.

6.101 Spring 2020 Lecture 411 Editing Components

Just right click the component

6.101 Spring 2020 Lecture 4 12 Editing Components

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

6.101 Spring 2020 Lecture 4 13 Editing Components

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

6.101 Spring 2020 Lecture 4 14 Selecting Device Model

There are no “ideal” BJT’s, MOSFET’s, etc. You can select a model (provided by LTspice), download models, or create your own.

6.101 Spring 2020 Lecture 4 15 Simulation: Transient

Transient simulation gives Voltage and/or Current vs.time.

These are transient parameters for a voltage source

6.101 Spring 2020 Lecture 4 16 Simulation: Transient

This is all you really need

6.101 Spring 2020 Lecture 4 17 Random Tangent: Parameters

You MUST define all of your parameters. This is a The “list” command allows you to choose parameter multiple values (simulation simulates each value separately). 6.101 Spring 2020 Lecture 4 18 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?

6.101 Spring 2020 Lecture 4 19 Here’s Where You Write the Solution

6.101 Spring 2020 Lecture 420 Here’s Where You Write the Solution

i2

i1 vo vx

i3

A DOUBLE POLE!!

6.101 Spring 2020 Lecture 4 21 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

6.101 Spring 2020 Lecture 4 22 Transient Simulation

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

**This is the current probe

6.101 Spring 2020 Lecture 4 23 Transient Simulation

1 kHz 10 kHz 100 kHz 1 MHz

6.101 Spring 2020 Lecture 4 24 AC Simulation AC simulation gives Voltage and/or Current vs.frequency. This is the AC parameter. Just set the amplitude to 1

6.101 Spring 2020 Lecture 4 25 AC Simulation

6.101 Spring 2020 Lecture 4 26 Extra Fun: Math in LTspice

Remember:

6.101 Spring 2020 Lecture 4 27 Transient Simulation

It’s the same as before!

6.101 Spring 2020 Lecture 4 28 Even More Fun

*Note: You can try out some math functions in the simulator window, too! (ex: V(Vo)/V(Vi)). 6.101 Spring 2020 Lecture 4 29 AC Simulation

6.101 Spring 2020 Lecture 4 30 Temperature as a Variable

• PTAT current source

6.101 Spring 2020 Lecture 431 Temperature as a Variable

6.101 Spring 2020 Lecture 432 Including External Models

• PFET model • Includes parameters to describe MOS device physics

6.101 Spring 2020 Lecture 433 Making Things Pretty

6.101 Spring 2020 Lecture 4 34 Making Things Pretty

6.101 Spring 2020 Lecture 4 35 Making Things Pretty

Bob Reay of Linear Technology has provided a nifty tool on his website to give LTspice circuits an even better makeover: http://reaylabs.com/tools/SchematicViewer/SchematicViewer.html

Before:

6.101 Spring 2020 Lecture 436 Making Things Pretty

Bob Reay of Linear Technology has provided a nifty tool on his website to give LTspice circuits an even better makeover: http://reaylabs.com/tools/SchematicViewer/SchematicViewer.html

After:

6.101 Spring 2020 Lecture 437 LTspice Secrets

Many aspects and functions of LTspice are not documented. You can learn lots of interesting undocumented capabilities of LTspice from: http://ltwiki.org/?title=Undocumented_LTspice

Of particular interest should be B-sources. These allow you to make devices such as non-linear resistors whose value is determined from a function of voltage, current, if statements, constants, etc. Though you cannot build these, they may be useful to model a part not available in LTspice, or to model a special function in your circuit you have not designed yet.

6.101 Spring 2020 Lecture 438 Questions??

6.101 Spring 2020 Lecture 439 LTspice HotKeys Simulator Directives – Dot Commands Command Short Description Schematic Symbol Waveform Netlist .AC Perform a Small Signal AC Analysis ESC – Exit Mode ESC – Exit Mode .BACKANNO Annotate Subcircuit Pin Names on Port Currents F3 – Draw Wire .DC Perform a DC Source Sweep Analysis F5 – Delete F5 – Delete F5 – Delete .END End of Netlist s

e F6 – Duplicate F6 – Duplicate

d .ENDS End of Subcircuit Definition o F7 – Move F7 – Move .FOUR Compute a Fourier Component M F8 – Drag F8 – Drag .FUNC User Defined Functions F9 – Undo F9 – Undo F9 – Undo F9 – Undo .FERRET Download a File Given the URL Shift+F9 – Redo Shift+F9 – Redo Shift+F9 – Redo Shift+F9 – Redo .GLOBAL Declare Global Nodes Ctrl+Z – Zoom Area Ctrl+Z – Zoom Area Ctrl+Z – Zoom Area .IC Set Initial Conditions Ctrl+B – Zoom Back Ctrl+B – Zoom Back Ctrl+B – Zoom Back .INCLUDE Include another File Space – Zoom Fit Ctrl+E – Zoom Extents .LIB Include a Library Ctrl+G – Toggle Grid Ctrl+G – Toggle Grid Ctrl+G – Goto Line # .LOADBIAS Load a Previously Solved DC Solution

iew U – Mark Unncon. Pins Ctrl+W – Attribute Window ‘0’ – Clear .MEASURE Evaluate User-Defined Electrical Quantities V A – Mark Text Anchors Ctrl+A – Attribute Editor Ctrl+A – Add Trace .MODEL Define a SPICE Model Atl+Click – Power Ctrl+Y – Vertical Autorange Ctrl+R – Run Simulation .NET Compute Network Parameters in a .AC Analysis Ctrl+Click – Attr. Edit Ctrl+Click - Average .NODESET Supply Hints for Initial DC Solution Ctrl+H – Halt Simulation Ctrl+H – Halt Simulation Ctrl+H – Halt Simulation .NOISE Perform a Noise Analysis R – R – Rectangle Command Line Switches .OP Find the DC Operating Point C – C – Circle .OPTIONS Set Simulator Options Flag Short Description L – L – Line .PARAM User-Defined Parameters - Use ASCII .raw files. (Degrades performance!) D – A – Arc .SAVE Limit the Quantity of Saved Data -b Run in batch mode. e G – GND .SAVEBIAS Save Operating Point to Disk S – Spice Directive -big or -max Start as a maximized window

lac .STEP Parameter Sweeps

P -encrypt Encrypt a model library T – Text T – Text .SUBCKT Define a Subcircuit -FastAccess Convert a binary .raw file to Fast Access Format F2 – Component .TEMP Temperature Sweeps -netlist Convert a schematic to a netlist F4 – Label Net .TF Find the DC Small-Signal Transfer Function -nowine Prevent use of () workarounds Ctrl+E – Mirror Ctrl+E – Mirror .TRAN Do a Nonlinear Transient Analysis -PCBnetlist Convert a schematic to a PCB netlist Ctrl+R – Rotate Ctrl+R – Rotate .WAVE Write Selected Nodes to a .WAV file -registry Store user preferences in the registry ©2018 , Inc. All rights reserved. Trademarks and -Run Start simulating the schematic on open Suffix Suffix Constants registered trademarks are the property of their respective owners. Ahead of What’s Possible is a trademark of Analog Devices. -SOI Allow MOSFET’s to have up to 7 nodes in subcircuit f 1e-15 E 2.7182818284590452354 LTspice-6/18(E) -uninstall Executes one step of the uninstallation process T 1e12 p 1e-12 Pi 3.14159265358979323846 analog.com -wine Force use of WINE(Linux) workarounds G 1e9 n 1e-9 K 1.3806503e-23 Meg 1e6 u 1e-6 Q 1.602176462e-19 LTspice K 1e3 M 1e-3 TRUE 1 Mil 25.4e-6 FALSE 0 LTSPICE SHORTCUTS ON A MAC 11/5/2013 REV 3 a DRAW CIRCLE b BUS TERMINATION g l DRAW LINE s ADD SPICE DIRECTIVE (right click for HELP ME EDIT) t ADD TEXT COMMENT w DRAW BOX z H HIDE LTSPICE z L SPICE LOG z N NEW SCHEMATIC z O OPEN z Q QUIT LTSPICE z S SAVE z Z UNDO ⇧z Z REDO z M MINIMIZE ⌥z M MINIMIZE ALL z W CLOSE ⌥z W CLOSE ALL z P PRINT ⇧z P page seupt

F2 COMPONENT F3 WIRE F4 NET NAME F5 DELETE F6 DUPLICATE F7 MOVE (CNTRL-R to rotate, CNTRL-E to mirror) F8 DRAG (CNTRL-R to rotate, CNTRL-E to mirror) F9 UNDO ⇧F9 REDO

SPACE BAR ZOOM TO FIT 2 FINGER PINCH ZOOM IN 2 FINGER SPREAD ZOOM OUT

Here are the modifier key symbols you may see in OS X menus: z COMMAND ⌥ ALT OR OPTION ⇧ SHIFT