2020-12-27 22:59:15 +01:00
|
|
|
<!DOCTYPE html>
|
|
|
|
|
<html>
|
|
|
|
|
<head>
|
|
|
|
|
<title>XSCHEM TUTORIAL: Backannotation of ngspice simulation data</title>
|
|
|
|
|
<link rel="stylesheet" type="text/css" href="xschem_man.css" />
|
|
|
|
|
<style type="text/css">
|
|
|
|
|
/* Local styling goes here */
|
|
|
|
|
p{padding: 15px 30px 10px;}
|
|
|
|
|
</style>
|
|
|
|
|
|
|
|
|
|
</head>
|
|
|
|
|
<body>
|
|
|
|
|
|
|
|
|
|
<!-- start of slide -->
|
|
|
|
|
<div class="content">
|
|
|
|
|
<!-- navigation buttons -->
|
|
|
|
|
<a href="xschem_man.html" class="home">UP</a>
|
|
|
|
|
|
|
|
|
|
<!-- slide title -->
|
|
|
|
|
<h1> TUTORIAL: Backannotation of NGSPICE simulation operating<br>point data into an XSCHEM schematic</h1>
|
|
|
|
|
<p>
|
2020-12-28 02:52:44 +01:00
|
|
|
The objective of this tutorial is to show into the schematic the operating point data (voltages currents,
|
|
|
|
|
other electrical parameters) of a SPICE simulation done with the
|
|
|
|
|
<a href="https://sourceforge.net/projects/ngspice/">Ngspice</a> simulator.
|
|
|
|
|
This tutorial is based on the <kbd>cmos_example.sch</kbd> example schematic located in the <kbd>examples/</kbd>
|
|
|
|
|
directory. Start Xschem from a terminal since we need to give some commands in this tutorial.
|
2020-12-27 22:59:15 +01:00
|
|
|
</p>
|
2020-12-28 02:52:44 +01:00
|
|
|
<img style="box-shadow:none;" src="backannotation1.svg">
|
2020-12-27 22:59:15 +01:00
|
|
|
|
2020-12-28 02:52:44 +01:00
|
|
|
<h3> CONFIGURATION </H3>
|
|
|
|
|
<p>
|
|
|
|
|
Open your <kbd>xschemrc</kbd> file (usually <kbd>~/.xschem/xschemrc</kbd>), go to the end of the file,
|
|
|
|
|
Ensure the following tcl file is appended to the list of scripts loaded on startup by Xschem:
|
|
|
|
|
<pre class="code">
|
|
|
|
|
#### list of tcl files to preload.
|
|
|
|
|
lappend tcl_files ${XSCHEM_SHAREDIR}/ngspice_backannotate.tcl
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3> SETUP </H3>
|
|
|
|
|
<p>
|
|
|
|
|
Select the 'STIMULI' code block (click on it) and edit its attributes (press <kbd>q</kbd> or
|
|
|
|
|
<kbd>Shift-q</kbd>):
|
|
|
|
|
</p>
|
|
|
|
|
<pre class="code">
|
|
|
|
|
.temp 30
|
|
|
|
|
** models are generally not free: you must download
|
|
|
|
|
** SPICE models for active devices and put them into the below
|
|
|
|
|
** referenced file in netlist/simulation directory.
|
|
|
|
|
.include "models_cmos_example.txt"
|
|
|
|
|
.control
|
|
|
|
|
<span style="color: red;"> op </span>
|
|
|
|
|
<span style="color: red;"> save all </span>
|
|
|
|
|
<span style="color: red;"> write cmos_example.raw </span>
|
|
|
|
|
.endc
|
|
|
|
|
</pre>
|
|
|
|
|
<p>
|
|
|
|
|
The important parts are in red in above text. This ensures all variables are saved into the raw file.
|
|
|
|
|
These instructions are for an interactive ngspice run.<br>
|
|
|
|
|
When done open the <kbd>Simulation-> Configure simulators and tools</kbd> dialog box and ensure the
|
|
|
|
|
<kbd>Ngspice</kbd> simulator is selected (not Ngspice batch). Also ensure the spice netlist mode is
|
|
|
|
|
selected (<kbd>Options -> Spice netlist</kbd>).
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation2.png">
|
|
|
|
|
|
|
|
|
|
<h3> SIMULATION </H3>
|
|
|
|
|
<p>
|
|
|
|
|
If you now press the <kbd>Netlist</kbd> followed by the <kbd>Simulate</kbd> button simulation should complete
|
|
|
|
|
with no errors.
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation3.png">
|
|
|
|
|
<p>
|
|
|
|
|
You can close the simulator since we need only the <kbd>cmos_example.raw</kbd> file that is now saved
|
|
|
|
|
in the simulation directory (usually <kbd>~/.xschem/simulations/cmos_example.raw</kbd>).<br>
|
|
|
|
|
Now verify that xschem is able to read the raw file: issue this command in the xschem console:<br>
|
|
|
|
|
<kbd>ngspice::annotate</kbd>
|
|
|
|
|
</p>
|
|
|
|
|
<pre class="code">
|
|
|
|
|
xschem [~] ngspice::annotate
|
|
|
|
|
Raw file read ...
|
|
|
|
|
xschem [~]
|
|
|
|
|
</pre>
|
|
|
|
|
<p>
|
|
|
|
|
If there are no errors we are ready and set.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3> PUSH ANNOTATION METHOD </H3>
|
|
|
|
|
<p>
|
|
|
|
|
Start placing some probe elements into the schematic.
|
|
|
|
|
The first element is the <kbd>devices/spice_probe.sym</kbd> component. This must be attached to
|
|
|
|
|
some schematic wires to show the voltage value.
|
|
|
|
|
</p>
|
|
|
|
|
<img style="box-shadow:none;" src="backannotation4.svg">
|
|
|
|
|
<p>
|
|
|
|
|
Place some of these elements on various nets, issue the above mentioned <kbd>ngspice::annotate</kbd>
|
|
|
|
|
command and see the voltage values in the schematic.
|
|
|
|
|
</p>
|
|
|
|
|
<img style="box-shadow:none;" src="backannotation5.svg">
|
|
|
|
|
<p>
|
|
|
|
|
Another useful component is the <kbd>devices/ammeter.sym</kbd> one which allow to monitor branch currents.
|
|
|
|
|
Break some wires and insert this component as shown here:
|
|
|
|
|
</p>
|
|
|
|
|
<img style="box-shadow:none;" src="backannotation6.svg">
|
|
|
|
|
<p class="important">
|
|
|
|
|
IMPORTANT: When inserting current probes the circuit topology changes (new nodes are created) so you need to
|
|
|
|
|
re-create the netlist and re-run the simulation
|
|
|
|
|
</p><br>
|
|
|
|
|
<p>
|
|
|
|
|
Doing again the <kbd>ngspice::annotate</kbd> command after simulation will update the ammeters showing
|
|
|
|
|
the branch currents.
|
|
|
|
|
</p>
|
|
|
|
|
<img style="box-shadow:none;" src="backannotation7.svg">
|
|
|
|
|
<p>
|
|
|
|
|
These voltage and current values are inserted in the probe components as <b>attributes</b> and thus can be saved
|
|
|
|
|
to file. Remember that if you change the circuit the values shown in the probe elements are no longer valid,
|
|
|
|
|
you should update the values with a new simulation + annotate operation when done with the changes.<br><br>
|
|
|
|
|
What i have described so far is the simplest annotation procedure based on a <b>push</b> method: a tcl script
|
|
|
|
|
reads the simulation raw file and 'pushes' voltage and current values into the probe components as instance
|
|
|
|
|
attributes. If you do an edit attribute on one of these elements you see the attribute 'pushed' into it by the
|
|
|
|
|
annotate script. The advantage of this method is that values pushed into probes can be saved to file and are
|
|
|
|
|
thus persistent.
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation8.png">
|
|
|
|
|
|
|
|
|
|
<h3> PULL ANNOTATION METHOD </H3>
|
|
|
|
|
<p>
|
|
|
|
|
There is another annotation procedure that is based on a <b>pull</b> method: the probe objects have tcl commands
|
|
|
|
|
embedded that fetch simulation data from a table that has been read by the annotate script.
|
|
|
|
|
</p>
|
2020-12-27 22:59:15 +01:00
|
|
|
|
2020-12-28 02:52:44 +01:00
|
|
|
<p>
|
|
|
|
|
To ensure all currents are saved modify the <kbd>STIMULI</kbd> attributes as follows:
|
|
|
|
|
</p>
|
|
|
|
|
<pre class="code">
|
|
|
|
|
.temp 30
|
|
|
|
|
** models are generally not free: you must download
|
|
|
|
|
** SPICE models for active devices and put them into the below
|
|
|
|
|
** referenced file in netlist/simulation directory.
|
|
|
|
|
.include "models_cmos_example.txt"
|
|
|
|
|
.option savecurrents
|
|
|
|
|
.save all
|
|
|
|
|
.control
|
|
|
|
|
op
|
|
|
|
|
write cmos_example.raw
|
|
|
|
|
.endc
|
|
|
|
|
</pre>
|
|
|
|
|
<p>
|
|
|
|
|
Remove all previous probe elements and place some <kbd>devices/ngspice_probe.sym</kbd> components
|
|
|
|
|
and some <kbd>devices/ngspice_get_value.sym</kbd> components.
|
|
|
|
|
the ngspice_probe.sym is a simple voltage viewer and must be attached to a net. The ngspice_get_value.sym
|
|
|
|
|
displays a generic variable stored in the raw file. This symbol is usually placed next to the referenced
|
|
|
|
|
component, but does not need to be attached to any specific point or wire.
|
|
|
|
|
Edit its attributes and set its <kbd>node</kbd> attribute to an existing saved variable in the raw file.
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation9.png">
|
|
|
|
|
<p>
|
|
|
|
|
Run again the simulation and the <kbd>ngspice::annotate</kbd> command and values will be updated.
|
|
|
|
|
</p>
|
2020-12-28 03:39:31 +01:00
|
|
|
<img style="box-shadow:none;" src="backannotation10.svg">
|
2020-12-28 02:52:44 +01:00
|
|
|
<p>
|
|
|
|
|
You can add additional variables in the raw file , for example modifying the .save instruction:<br>
|
|
|
|
|
<kbd>.save all @m4[gm] @m5[gm] @m1[gm]</kbd>
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation11.png">
|
|
|
|
|
<p>
|
|
|
|
|
Data annotated into the schematic using these components allows more simulation parameters to be viewed into
|
|
|
|
|
the schematic, not being restricted to currents and voltages. Since these components get data using a pull method
|
|
|
|
|
data is not persistent and not saved to file. After reloading the file just do a <kbd>ngspice::annotate</kbd>
|
|
|
|
|
to view data again.
|
|
|
|
|
</p>
|
2020-12-27 22:59:15 +01:00
|
|
|
|
2020-12-28 02:52:44 +01:00
|
|
|
<p>
|
|
|
|
|
There is one last probe component, the <kbd>devices/ngspice_get_expr.sym</kbd>. This is the most complex one, and
|
|
|
|
|
thus also the most flexible. It allows to insert a generic tcl expression using spice simulated data to report
|
|
|
|
|
more complex data. In the example below this component is used to display the electrical power of transistor m3,
|
|
|
|
|
calculated as <kbd>V(GN) * Id(m3)</kbd>.
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation12.png">
|
|
|
|
|
<p>
|
|
|
|
|
The example shown uses this component to display a (meaningless, but shows the usage) gm ratio of 2 transistors:
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation13.png">
|
|
|
|
|
<p>
|
|
|
|
|
The syntax is a bit clompex, considering the verbosity of TCL and the strange ngspice naming syntax, however
|
|
|
|
|
once a working one is created changing the expression is easy.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p class="important">
|
|
|
|
|
To avoid the need of typing commands in the xschem console a launcher component <kbd>devices/launcher.sym</kbd>
|
|
|
|
|
can be placed with the tcl command for doing the annotation. Just do a <kbd>Ctrl-Click</kbd> on it to trigger
|
|
|
|
|
the annotation.
|
|
|
|
|
</p>
|
|
|
|
|
<img src="backannotation14.png">
|
|
|
|
|
<br>
|
|
|
|
|
<br>
|
|
|
|
|
<br>
|
|
|
|
|
<br>
|
2020-12-27 22:59:15 +01:00
|
|
|
|
|
|
|
|
<!-- end of slide -->
|
|
|
|
|
<div class="filler"></div>
|
|
|
|
|
</div>
|
|
|
|
|
<!-- frame footer -->
|
|
|
|
|
<iframe seamless src="xschem_footer.html" class="footer_iframe" >
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
|
|
|
|
|
