Black Box Electronics
An Introduction to Applied Electronics for Physicists
5. Pushing the Limits With Spice
University of Toronto
Quantum Optics Group
Alan Stummer, Research Lab Technologist
June, 2005
Spice Programs
• 5 Spice*:
Free for non-commercial use with basic version, simple to
use, effective, easy to add new models. www.5spice.com
• Linear Technology – LTSpice et al:
Free, heavy bias
towards Linear Tech’s products, hard to add new models. www.linear.com
• National Semiconductor – WebBench:
Free, online
only, exclusively National’s components. Limited circuits.
www.national.com
• Kemet:
Free, exclusively Kemet’s capacitors in frequency domain only
but very simple and useful. www.kemet.com
• PSpice:
Top price, most features, slightly bloated, need both models
and symbols.
* 5 Spice is used in this talk.
2
Common Simulations
• DC Bias:
Steady state V and I at t=-0. All capacitors ignored,
all inductors shorted. No graphs, tabular results only.
• DC:
Same as “DC Bias” except one or more DC sources may be
swept through a voltage range.
• AC:
Frequency domain. Sweep one or more AC sources
through a frequency range.
• Transient:
Time domain. Between fixed times. Can also
sweep components’ parameter(s).
• Monte Carlo:
Time or frequency domain with random
selection of any or all component parameters within their specified
tolerances. Not available on 5 Spice.
3
Spice Sequence
1.
2.
3.
4.
5.
Draw schematic.
Select type of simulation.
Run simulation.
Adjust component values.
Repeat with other types of simulation.
4
Adding Components
Move the
mouse over
the icon to
select
supplies,
click on
fixed DC.
5
Add DC Supply
Wires
Passives
Actives
Opamps etc.
Supplies
Test Points
Text, nets
Logic
Drag and drop
a Constant
Voltage (AKA
DC) symbol.
Double click to
give name and
set voltage.
6
Connect Supply
Add ground and
supply net,
rename net.
Right click,
move label field
to more esthetic
location.
7
Add Photodiode Model
Add Current
Source and
capacitance
to simulate a
photodiode.
8
Add Generic Opamp
From here…
…add opamp
subcircuit
symbol. Mirror
and rotate for
standard
orientation.
9
Select LM324
Double click
symbol. Set
“ref des”,
select LM324
model.
This is the
model file.
10
Connect Opamp
Add supply
and ground.
Connect to
PD. Add RC
feedback.
11
Add Test Point
Monitor this
node, call it
“Monitor”.
12
DC Bias “Sanity” Check
Select Analysis
Dialog (F8), select
DC Bias analysis.
Run analysis.
Read tabular
results or with
mouse over
node.
13
Define Photodiode
Double click
Ipd symbol.
Add the DC
Analysis
parameters.
14
Select DC Analysis
Select New
Analysis, add
DC Analysis,
can rename
it. Enable Ipd
source.
15
Select DC Analysis
On Graph tab,
select the
Monitor test point
and use left axis.
Defaults to
autoscaling. Hit
Enter or Ok and
then Run (F9).
16
Run DC Analysis
Run the DC
analysis.
Move the
cursor to
read XY
values.
OOPS!
Discontinuity
at low
power, poor
saturation.
17
Try Another Opamp – AD8605
Double click
and try
another
opamp, the
AD8605.
18
DC Analysis With AD8605
Note good
linearity at low
levels and
great output
saturation.
Keep the
AD8605
opamp.
19
Add Second Stage
Copy first stage,
paste as second,
change ref des
on all parts.
Rescale Ipd.
Second stage
voltage gain is
+101. Add
realistic load.
20
View DC Analysis
Note slight tilt in
second stage at
low power and
output saturation
with the added
1KΩ load.
This circuit is
acceptable for
DC performance!
21
Prepare Transient Analysis
Double click Ipd.
Select Transient
analysis,
Piecewise
waveform, define
the waveform.
Note double
10Sec as 10- and
10+.
22
Transient Analysis
Select Transient
analysis.
Enable the Ipd
source, set start
and finish times
plus optional
step interval
time, enable the
Helpers, setup
the Graph.
23
Run Transient Analysis
Works, but is
very very slow,
takes 10
seconds to be
stable.
Note manual
scaling of both
Y-axis.
24
Adjust Circuit Timing
Change caps to
100 times
smaller, adjust
Ipd timing to 100
times faster. Do
same to Analysis
Dialog, now 0 to
200mS.
25
Final Transient Analysis
Reasonable
timing,
reasonable gain.
This circuit has
been adequately
simulated.
26
High Speed Crash
Like before,
component
values changed
for 100 times
faster again.
Note step of 1st
stage at start, but
hidden (damped)
by 2nd stage.
Too fast!
27
Extending the Model
Add a voltage
source to
simulate a
range of Vio
(input offset
voltage). This
one is swept
±0.5mV in
25uV steps.
28
Extended Model Results
Note how 2nd
stage output
crosses Y-axis
below zero, and
how Spice
already added
some Vio. May
want to add an
offset to always
force above
zero or can just
ignore.
29
Trouble in Paradise
No convergence!
Spice is at fault,
not the circuit.
Try opening the
Analysis Dialog
(F8) and change
setup until it
works. Try the
Project Dialog
Wizard. Try
minor changes to
component
values. Good
luck!
30
Ω The End Ω
Thanks for coming!
And thanks for the loan of the laptop, Paul!
31