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 Integrated
Circuit 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 4 2
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 resistors, capacitors, and
inductors 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 4 10
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 4 11
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 4 20
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 4 31
Temperature as a Variable
6.101 Spring 2020 Lecture 4 32
Including External Models
• PFET model
• Includes
parameters to
describe MOS
device physics
6.101 Spring 2020 Lecture 4 33
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 4 36
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 4 37
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 4 38
Questions??
6.101 Spring 2020 Lecture 4 39
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
F6 – Duplicate F6 – Duplicate .ENDS End of Subcircuit Definition
F7 – Move F7 – Move .FOUR Compute a Fourier Component
M odes
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
U – Mark Unncon. Pins Ctrl+W – Attribute Window ‘0’ – Clear .MEASURE Evaluate User-Defined Electrical Quantities
View
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 – Resistor R – Rectangle .OP Find the DC Operating Point
C – Capacitor C – Circle
Command Line Switches
.OPTIONS Set Simulator Options
Flag Short Description
L – Inductor L – Line .PARAM User-Defined Parameters
-ascii Use ASCII .raw files. (Degrades performance!)
D – Diode A – Arc .SAVE Limit the Quantity of Saved Data
G – GND -b Run in batch mode.
.SAVEBIAS Save Operating Point to Disk
S – Spice Directive -big or -max Start as a maximized window
.STEP Parameter Sweeps
Pl a ce
T – Text T – Text -encrypt Encrypt a model library
.SUBCKT Define a Subcircuit
F2 – Component -FastAccess Convert a binary .raw file to Fast Access Format
.TEMP Temperature Sweeps
F4 – Label Net -netlist Convert a schematic to a netlist
.TF Find the DC Small-Signal Transfer Function
Ctrl+E – Mirror Ctrl+E – Mirror -nowine Prevent use of WINE(Linux) workarounds
.TRAN Do a Nonlinear Transient Analysis
Ctrl+R – Rotate Ctrl+R – Rotate -PCBnetlist Convert a schematic to a PCB netlist
.WAVE Write Selected Nodes to a .WAV file
-registry Store user preferences in the registry
©2018 Analog Devices, 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 GROUND
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
