Using the Schematic Entry Tool to Create Circuits
The Elements Panel
The Work Area
Connecting Elements
Editing Elements
Converting to Netlist
Schematic Variants
Device Models
The schematic entry tool (SET) enables you to create circuits graphically,
instead of typing netlists. However, before the schematic circuit can be
simulated it has to be converted into a netlist, which is then fed to the
simulator tool. Since analysis tasks can not yet be specified in the SET
you have to manually add them to the netlist after the schematic has been
converted.
The Elements Panel
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The elements panel contains all circuit elements, which can be
copied to the work area. It also includes three control buttons
and a slider to adjust the transparency of the panel. Open the
elements panel by clicking on the Elements button in the toolbar
or by selecting Show Elements from the Window menu.
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Circuit elements
are organized in groups (e.g., transistors, diodes, power sources).
The elements you see in the panel are the current selected elements
from their groups. To see all elements of a group simply right-click
(or CTRL+click) on the visible element. A popup menu appears and you
can choose another element.
The slider at the bottom adjusts the panel's transparency. This could
be useful in situations where the panel is positioned in front of the
schematic due to limited desktop space.
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The Work Area
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The work area is where you create your circuit. To add elements to the
work area simply drag and drop it from the elements panel. To move
circuit elements within the work area either drag them with the
mouse or use the arrow keys for more precise positioning. When using
the arrow keys you can move faster by additionally pressing the Shift key
( ).
Unlike most schematic tools MI-SUGAR uses no grid. Instead, there are
placement guides to help you align the circuit elements. These guides
are vertical and horizontal green lines and appear whenever two
connection points align. When moving a selection of multiple elements
this feature works only for the one element which is under the mouse
pointer.
To select multiple elements either click on the desired
elements while pressing the Command key, ,
or draw a selection box around the elements by clicking on an empty
area and dragging from there.
The work area has a limited size. Border lines are drawn in orange.
You can navigate within in the work area by panning and zooming:
To pan the view click on an empty region of the work area, hold the mouse
button pressed for one second, then drag. You can also use the Option key,
, in combination with the arrow keys or drag with
the middle mouse button if you have a three-button mouse. Yet another way
is to click on one of the bars that appear when the mouse pointer comes close
to any of the four sides of the schematic view area in the window.
To zoom the view use the slider in the tool bar or the plus and minus
keys (+ , –). You can also use the scrollwheel of the mouse if you
have a mouse with scrollwheel. Note: A three-button mouse with scrollwheel
is highly recommended for MI-SUGAR.
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As a navigation help, clicking on the Home button in the toolbar
moves the view back to the lower left corner of the first quadrant of
the work area.
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Connecting Elements |
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Circuit elements have connection points which allow them
to be connected to other elements. A connection point is
highlighted in red when the mouse is on top of it. To connect
two elements click on the connection point of the first
element and drag the pointer to the connection point of the
other element. (If you wait longer than 1 second after clicking
on a connection point the mode automatically switches to
element dragging. Use this feature to drag very small elements,
like node elements, which are covered with connection points.)
After you start dragging, a connection line
will be drawn from the connection point to the mouse position as
long as you keep the mouse button pressed. The connection line
follows a three-point route. The originating connection point
and the mouse position are the first and the last points,
respectively. The middle point is chosen automatically so that
the connection line is split into a horizontal and vertical
component.
When the pointer is on top of an unconnected connection
point the connection line will turn red. Release the mouse button
to make the connection.
A connection point can only connect to one other connection point.
If the target point is already connected new connections will be
refused. Use node elements (in the elements panel) to connect multiple
points with each other.
To disconnect two elements drag the connecting line at one of
its two connection points and release over an empty region.
Tip: When you drop a node element on a connection line, the node
will be inserted at that point.
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Editing Elements
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The Info panel allows you to inspect schematic elements and
edit their properties. Open it by clicking on the Info
button in the toolbar or by selecting Show Info from the
Window menu.
All elements have a fixed type name and an editable label
and can be annotated with a comment. The info panel shows
these properties at the top, next to the buttons, which let
you rotate and flip elements and set the relative position
of their labels.
The area below these common fields depends on the type of the
inspected element. For subcircuits the namespace, the revision
and the pin-to-node assignment matrix are shown. For ordinary
circuit elements a table with editable device parameters
is shown. A resistor, for example, has the single parameter
resistance while more complex devices, like diodes and
transistors, have more parameters. Parameters can be edited by
double-clicking on its value field and typing a new value.
Values for the model parameter are selected from a list
(see Device Models).
Tip: To create an exact copy of an element press the Option
key ( ) and drag it with the mouse. Use this
feature to quickly generate a bunch of elements with the same
orientation, the same label, the same label position and the same
parameters. To copy
elements from one window to another use C
for copying the selected elements and V for
pasting. Note that the elements will be pasted to the same positions
they were copied from and that connection lines are not copied.
For elements with a single parameter the value can be viewed
directly in the schematic by pressing the space bar. Pressing the
space bar again hides the values.
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Converting to Netlist (Capturing)
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Clicking on the Capture button in the toolbar will convert the
schematic into a netlist, which replaces the previous content of the
netlist editor. The conversion process assigns node numbers to all
connection points of each circuit element. The same number is assigned
to all electrically equivalent points. Zero is assigned to all points
connected to ground, and -1 is assigned to unconnected points.
Control commands (.op, .ac, .tran, .dc, etc.) of an existing netlist will
be lumped together and placed right after the title line of the new netlist.
This allows you to quickly repeat an analysis task after making modifications
in the schematic.
After capturing the schematic you can view the assigned node numbers
directly on the schematic. Press the space bar to make the node
numbers visible. Press the space bar again to hide the node numbers.
Note: For now, the produced netlist is compatible with SPICE only.
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Schematic Variants
For each circuit you can have up to four schematics. Only
one of them can be active at a time. Although these four
schematics can be totally independent of each other the idea
behind having more than one schematic is to manage a set of
similar schematics. That's why they are referred to as
variants. Variants are especially useful when you have
one main schematic of a circuit and want to experiment with
modified versions, which require only minimal changes to the
netlist after capturing.
The four dots in the tool bar of the circuit window represent
the available schematic variants. The current active variant
is indicated with a red dot. The keys 1, 2, 3 and 4 are used
to switch from one variant to another. By pressing
1, 2,
3 or 4 you
replace a variant with a copy of the current variant.
Device Models
Device models are used to describe the electrical behavior of
circuit elements. Some models are more accurate than others or
more suitable for a specific analysis task.
SPICE lets you specify the device model of a circuit element
and its parameter values in the netlist. But you don't need to
because MI-SUGAR supports device model assignment in the schematic:
Elements with selectable models have the Model parameter
and it can be set in the info panel by selecting a model from the
popup list.
You can manage your personal model repository in the Device
Models window. To open the device models window select
Show Device Models in the Window main menu.
You will see a list of device model names on the left side and
the parameter values of the selected model on the right.
The content on the right is freely editable and will be inserted
into the netlist during schematic capture. This means that you
can use comment lines if you want to. Please note that the
keyword .model, the name of the model and the opening
and closing parantheses must not be included in the parameter list
and each new line must start with a plus (+) symbol.
To create new device models make copies of one or more existing
models by selecting their names in the list and clicking on the
Copy toolbar item. Double-click on each copied item to
change its name. To delete device models: Select their names from
the list and click on the delete button in the toolbar.
For each category of devices a default device model is included.
These default models can not be deleted or renamed.
Selected device models can be exported to a file by clicking on
Export, and then choosing/setting a target file name.
Other users can import those exported device models by clicking
on Import and selecting the previously created device models
file. The device model collection used by MI-SUGAR is stored
in the file Device Models in the folder Application Support
(in the folder Library in your home directory). It is
read from during startup and saved to when quitting.
When a schematic has elements that use non-default
device models the device models are included in the
saved file and will be added automatically to other
user's device model libraries when they open the file.
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