========ANALOG
ART===================
1) Productivity
Tools and Templates
In Electronics there always seems to be opportunity to spend time to
save time.
Some times it is far easier to just create yourself
a tool in order to save a lot of work.
A) RR Polish calculator
B) R_C_F calculator
C) R_C_L_F
calculator
D) Javascript Calculators
Getting
something to work often requires far more attention to detail
than the help files provide.
Working examples need to have all the required details in
place just to work.
The following "work in progress" organized working examples intended
for cut and paste use.
A) macspice/winspice Template web page
B) SIMetrix
Template web page
C)
javascript
Template web page
D) Perl
Template web page
E) Ccode
Template web page
F) Xcode
Template web page
G) Web Page
Template web page
H)
Icarus Verilog Template web page
I) LabView
Template web page
J) ICEDIT
Template web page
K) Quartz
Template web page
2) Free Spice
Several free or semi-free versions of spice are
available off the web.
SIMetrix is a cadence/pspice
like limited free version
for
windows.
Macspice is a spice-standard
free version
for
OS X which allows scripting.
Winspice is the spice-standard free
version
for windows which almost works
using the same code.
This simple little PLL transient simulation runs off the exact
same code.
3) Spice Models QA
The design engineer using a model is the really the one responsible for
the model being accurate.
Sometimes the TC of a diode needs to be sanity checked
in order to design a bandgap reference.
Matching a model to a curve tracer
is typically the first thing to do.
The extended bipolar dynamic range of
today's BiCMOS makes a Gummel Poon
Plot more critical.
4) Spice Scripting
Designing something like an Op Amp requires testing a circuit
over all the "corners".
Many permutations need to be tested because a
design will typically fail at a subtle "corner condition".
The permutations typically involves
3 temperatures, 2 supply voltages, multi-applications, and several
"process corners".
A scripting ability in Spice allow the changing of
its internal simulation conditions on the fly.
This enable a single
multi dimensional simulation to effectively test
everything.
The results can be stored in a text file which can
be further processing by a perl program.
Simulators such as Macspice/Winspice and cadence
(Ocean)
and SIMetrix(not_free) allows
scripting.
The scripting resource can be used to do
customized testing of things like THD,
capacitance, and F_tau.
5) BSIM4 simplified
The latest BSIM4 manual off the web
describes about 300 model parameters.
If one downloads the following 180nm to 22nm
BSIM files off the web.
That adds up
3300
BSIM model parameters which may or not may be critical .
It would be convenient if all the data could be
reorganized as a table.
Acrobat Pro allows the
conversion of a pdf file to the following
text file which has been slightly cleaned up.
A
simple perl program can dump all
the model files into
a single
text file.
Another perl program can use
the previous two text files to create a
table of all parameters versus process.
The
table can further be color coded
to view the trends.
6) PERL and text files
Production test data for an Analog IC is usually available as a text
file.
The previous BSIM4
simplified example shows how perl can read and reorder text
data
such as a data log.
This feature can also come in handy for the previous Spice Automatic Testing example.
The previous perl program that combines
directories into a single text file gets a lot of use.
Another handy program can reorganize
the data within a single text file.
7) The Most Beautiful
Equation in the World.
Euler identity
has been described by some as "the Most Beautiful Equation in the
World".
A FFT is really just mapping analog signal to Euler identity.
This can be better seen when the results of
a FFT is plotted in 3D.
A javascript calculator as been
developed which can also do the 3D plotting.
8) Transient Noise Simulations
Spice programs like SIMetrix
allow noise to be simulated in transient analysis
.
For spice programs like Macspice/Winspice, a RandomPWL javascript can created
the data.
SPICE can read the PWL file and simulate and plot both
transient and spectrum results.
Using a Noise Transient Analysis, it is possible
to see how two noise sources add together.
9) THD Simulation using Sprectrum Analysis
Simulating THD in
transient analysis shows the
actual distorted waveforms.
Selected elements of the spectrum output
can be mathematically processed to get THD .
The classical
distortion over
temperature of a differential input is a good place to start.
Adjustments of area ratios for distortion cancellation
for an alternative input can also be viewed.
The distortion profile of differential input stages all track
absolute temperature.
10) Extremely Easy Ways to Generate Spice
Waveforms
By making a voltage ramp that tracks time, waveforms can be generated
using equations.
Some examples are Triangle waves, Square waves, and Ramp
waveforms .
This can be extended to making PWM waves that can also be made to be in sync .
Equations for Amplitude
Modulation and Phase modulation also work.
But this makes it real easy to Sweep
Parameters of the Input Signal over time.
11) Play with Transmission Line Reflections
The EDN
trade
magazine has written some good articles about Time-domain reflectometry.
Modeling transmission lines as LC subcircuits
may give some vision as
to what is happening .
The various impedance mismatches
can be all simulated.
The results are all the same but all
internal node voltages and currents are visible.
The cable speed appears to simply
track the time constants of resonance elements.
Identifying and tweeking out cable discontinuities
can also be played with.
12) Watch Noise Cancelation Work Inside an
Op Amp.
In negative feedback, an amplifier will try to cancel out all internal
noise sources.
A Noise Transient Analysis applied to an
Amplifier
can show everything working .
Modeling an accurate Audio frequency Noise waveform
can be very useful .
Transistor
subcircuits can then be modeled to have their noise properly
track bias current.
Observing how current noise can be modeled
as input noise voltage is a good sanity check.
Noise
operating in an Operational Transconductance Amplifier
can also be observed.
13) Simulate a Pinch Resistor.
A subcircuit can be made to follow the equations of a pinch resistor.
14) The Balanced Low Voltage BandGap.
Need an accurate low voltage bandgap that works down to 900mV over temperature?
The age old design technique of balancing out errors
still works .
But balancing is only as good as it is possible
to know all the errors.
15) State Variable Filters Map Equations
to Circuit Components.
Relating the equations to the simple term of Q is a good
starting point.
The Q terms in the equation maps
to feedback in State Variable Filters.
The frequency terms map independently to the
integrator terms.
The equation works on
resistor ratios and not absolute values.
Operational
Transconductance Amplifier can replace the integrators
This allows voltage to
control the frequency of a State Variable
Filter.
It also allows complete IC integration of
analog audio frequency filters.
The mapping comes in handy making Butterworth and Bessel filters
16) FFT Your Company's Stock Using Spice
It is always nice to add REAL
Input Signal to a Spice Simulation.
It only requires a spreadsheet
and a text editor to input any data.
Software is being written to convert computers into oscilloscopes.
The line-in port can be used to digitize Audio frequency waveforms.
And USB hardware is being developed
to digitize higher frequencies.
17) Make Some Pretty Waveforms.
Generating Lissajous waveforms involves
using the X/Y features of spice.
Another X/Y oscilliscope
application is for BH curves.
18) Measure Stray Capacitance Within Spice.
The scripting features in Spice can be used to measure and print out capacitance.
This feature extends to measuring all
the strays capacitances within a MOS
device.
The feature further extends into making
a CV plot of gate capacitance.
19) Investigate f_tau Parameters using
Spice scripting.
Page 72 of the
Gummel-Poon Toolkit describes
the f-tau situation.
Observes the effects of changing TF or CJE or IKF or ITF or VTF or XTF.
20) Voltage Controlled Filters
State Variable
filters can vary their frequency if made using gm_C stages.
The Low Phase distortion of a Bessel filter will hold over all
VCF frequencies.
The flat pass band response for a Butterworth will hold as well.
The Phase distortion of a Butterworth
does change with VCF frequency.
21) Group Delay on Phase Distortion.
The
Bessel filter shows why good
group delay means low phase distortion.
The
Butterworth filter shows the
source of phase distortion.
22) New Thermal Concerns.
Silicon Oxide has
one tenth the thermal conductivity of silicon.
Oxide Isolation thermally isolates transistors.
This simulation investigates real lab measured thermal
self heating.
23) Simple Logic Functions in Spice.
Sometimes simple
logic
functions can be defined with a single spice line.
A folded ADC method can be used to do an ADC function.
Easy ways if decoder or flipflop functions are needed.
24) Interesting Effects of Distortion in
Filters
Distortion with feedback allows filter operation under multiple states
Chaos type plots can show these
effects in active filters.
Distortion also
can generate a
"hang on" and "snap back" effect
25) Translating Between FM and PM
Frequency
Modulation in Spice is really Phase Modulation
And Phase Modulation is really
Double Frequency
Modulation.
Don Sauer... DSauerSanJose@Aol.com
