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Simulate
In the Cutestudio family of EDA tools there are the following products:
- Circuit drawing program
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Simulation program
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Graph viewing program
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Integrated Sumo program
The integrated program has the following benefits:
- Graphs and circuits can be viewed simultaneously
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While a SUMOS-FUSION simulation is in progress, most schematic operations can still be performed
We advise the use of a decent widescreen monitor for best results.
The integrated product has got a little menu akin to the controls on a video recorder that allow you to start, pause and stop simulations and to perform runtime power analysis and DC quiescent simulations.
The integrated tool-bar:
The tool-bar allows facilities that are only in the 32bit version, and some that are also embedded in other menus to be accessed directly:
| Button | Action
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| This causes a DC analysis (quiescent or bias point) to be performed on the current circuit.
The voltages only are shown wherever the BIAS_VALUE type markers are placed:
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| This starts a simulation run, specified by fields in the SIMULATION menu. Only one simulation can be run at a time. Drawing functions can be performed during internal simulations.
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| This pauses a simulation. Other jobs that may be perhaps jerky or slow because of the added work the PC is doing will also speed up. The simulation status is still regarded as running, so other simulations cannot be run while the current one is paused.
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| This stops a simulation prematurely. Normally simulations will run their course and stop automatically, or a maths error will cause the run to be abandoned.
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| This has two effects:
- If no graphs are present, it brings up any previous results and the graph-viewer menu appears.
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If there are graphs present, the graph-viewer menu appears.
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| This closes all graphs and closes the graph-viewer menu if present.
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| This is related to the power system, which is a feature of the top integrated versions, and described below.
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Integrating component power dissipation
When you design a circuit you need to know what power rating to specify for each component, or indeed any necessity to change that circuit (to something more efficient for example)
Starting the power analysis
The simulation menu contains this symbol on a button next to the TR button.
When this is selected and an internal TR or transient (time-domain) analysis run is done, for each dissipating component the SUMOS-FUSION simulator adds up the energy at each time-step during the run and at the end divides it by the total run-time to find the average power.
Looking at the power use of each component
After the simulation has finished, pressing the icon on the main toolbar again yields a list of component vs power. It is then quite straight-forward to determine the power-consumption/dissipation for each component, enabling the manufacture of circuits with enhanced reliability and heat characteristics.
Note: This method of power measurement is based on numerical integration, and is therefore subject to more error than a purely analytical method.
Simulating
The SUMO interactive simulator is tightly integrated with the SUMO graphical viewer, which allows you to view results as they are calculated.
To successfully simulate a circuit, you need:
- A circuit complete with stimulus and a PROBE or METER
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A simulator selected
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A simulation domain must be selected;- AC, DC or TR
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Traces for graphs must be specified
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Sweeper/Monte-Carlo setup if enabled
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Click-on SIMULATE
Entering schematics of circuits is covered in an earlier section.
Specifying input stimuli
An input waveform is a transient source that is used to study the effect of putting signals into the circuit that is to be analysed.
The sources that can do this are:
 Voltage sources, and  Current sources.
Their value during a DC domain quiescent analysis or sweep is zero. Their value during an AC analysis is as shown on the circuit, i.e. their primary value. Their value during TR or time-domain analysis is defined by selecting the required waveform shape and setting it's parameters. Firstly, open the PARAMS menu by selecting the component (draw it in if required), and then either double-click on the source you have just drawn, or click-on PARAMS in the menu on the left hand side of the screen.
Once inside the PARAMS menu, select the field called 'Source type' and either double-click on it or press SET . This causes the SOURCE menu to be opened.
This waveform is a simulation of the waveform using the current transient simulation parameters, and therefore is affected by them.
The SOURCE menu gives the choice of all available transient sources, together with a small graph showing their time-domain waveform.
To set a source type, click on the top left list in the menu. The selected source type will then be used for the source and it's name displayed in the PARAMS menu entry, e.g. SIN, EXP . etc.
To set a source parameter, click on the entry in the list and then on SET, or just double-click on the entry. All source parameters can be values or expressions.
Selecting Simulators
Simulator selection is only available from SUMO-EXPERT.
Click on the simulator name in the top menu-bar....
and select the simulator that you wish to use. To switch to the selected simulator click-on SWITCH-TO . This will now become current.
Information about each simulator is stored in its .SIM file. The selected simulator must be installed properly before use. For example, if using a simulator whose name is 'SPICE', and lives in the directory 'C:\SPICE', then the PATH may need to be extended, i.e.:
PATH = C:\DOS;C:\WINDOWS;C:\SUMO;C:\SPICE
and is to be found in the C:\AUTOEXEC.BAT file on PCs. If the simulator is not correctly installed the message: 'Bad Command or Filename' will appear when SUMO tries to run it.
Details on editing SIM files is detailed later.
Simulation domains
There are three basic simulation domains :
Frequency response sweeps
AC looks at the frequency response of a circuit, and is often referred to as small signal AC. This is because there is an initial DC bias or quiescent simulation done first, automatically, to establish gains etc. to compute working models for the AC domain. Thus the AC simulation is not a true simulation of the devices, but of their behaviour based upon the quiescent state. Before running an AC simulation involving non-linear devices, make sure that the critical DC conditions are satisfied first. To do this, it is suggested running a very short DC sweep or transient simulation
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Time domain analysis
TR, transient or time domain simulations simulate the behaviour of a circuit in real time using lots of small time-slices. Exact values are possible from AC simulation, but TR simulation involves a trade off between complexity, error and speed, and various simulators will behave differently. If specifying a source such as VAC or IAC from the Parts-Bin, the source type selected from the parameters menu will be used, and the displayed value on the circuit is merely the AC domain value, which is ignored during TR simulation. When altering the waveform shapes, the waveform shown is based on a simulation of that source, and is affected by the TR simulation parameters.
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Sweeping a DC source
The DC domain is quiescent conditions analysis. A voltage or current source is swept through a set of values. For each step the quiescent conditions are computed and the PROBE s and METER s are output as results, so characterisation curves can be created.
Note:
If you have the Monte-Carlo /Sweeper option then sweep is used in a different context. For each pass of the Monte-Carlo run or the sweep, a complete simulation is done using whatever domain or combination of domains is selected.
Controlling the simulation
The SIMULATION menu (click on SIMULATE in the top level menu or press ALT-S) enables you to specify and start the simulation and it's results.
Select the domain(s) that you wish to use by clicking on AC and TR etc. All simulations represent a sweep of values, from a start value to a stop value. The step value can either be a step increment as in the case of the time domain, or the number of steps per decade, as in an AC logarithmic simulation. It is usually best to specify the number of output points required rather than the step.
To set any field, click on it, enter the required value, and then press OK .
Select a logarithmic or linear AC scale by clicking on the box next to AC . For DC sweeps, the source to sweep can be selected by clicking on the box next to DC .
Pressing SIMULATE causes the circuit to be saved, netlisted, and then calls the simulator. On exit, control is returned to the schematic editor. Pressing NETLIST only saves and creates a netlist file to use later. To view results that were just produced, without re-simulation, (e.g. perhaps after editing some trace expressions ) press VIEW .
When using the SUMO interactive simulator, auto-scaling of graphs is done in order to fit the axis values to fit the data properly. Auto-scaling can be minimised by switching RANGING off in the OPTIONS menu. Once a simulation is running, you cannot exit the application, even if paused, it must be stopped using STOP .
Simulator variables
The green components are PROBE s or METER s. Click on the green components in the Parts-Bin, and look at their names at the bottom. A PROBE is for measuring voltage at a point, a METER is for current, sensing the current flowing through as it is used to replace wire elements. If you have adjusted the colour palette in the SETUP program, or are running a monochrome display device, this is what they look like:
PROBE 
METER 
PROBEs and METERs are used by SUMO to get the target simulator to output results. A PROBE or a METER, combined with a type, forms a simulator variable . SUMO takes care of the combinations, the required variables can then simply be picked out from the supplied list of all possibilities.
Variable types (for PROBE and METER)
| Voltage | Type | Function | Scope | Current | Type | Function | Scope
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| VM | Voltage Magnitude | AC, TR, DC | | IM | Current Magnitude | AC, TR, DC
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| VP | Voltage Phase | AC | | IP | Current Phase | AC
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| VR | Voltage Real | AC | | IR | Current Real | AC
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| VI | Voltage Imaginary | AC | | II | Current Imaginary | AC
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| VDB | Voltage decibels | AC | | IDB | Current decibels | AC
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| VGD | Voltage Group Delay | AC | | IGD | Current Group Delay | AC
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For a probe called VP1, the variable of type 'voltage magnitude' is referred to as VMVP1. Thus SUMO will instruct the simulator to output this variable, if the voltage magnitude of VP1 is required. Within the AC domain simulation type, variable VP1 can produce six separate variables, because it can be of six different types.
The graphical output does not display variables, but traces . A trace is an expression, that can contain one or more variables.......
Defining Traces
SUMO can create any output of your choice, working from the standard variables detailed in the last section. Assuming that you are in the SIMULATION menu, (entered by pressing SIMULATE on the top menu-bar or typing ALT-S)
Press AC-TRACES , DC-TRACES or TR-TRACES to open the relevant domain's TRACES menu.
Default traces..
There are two fast methods of producing simulation output :
- Do not bother entering this menu. This will cause the default traces for all PROBEs and METERs (unless disabled in the OPTIONS menu) to be created.
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Enter this menu and press DEFAULTS . This deletes all traces (in this domain) and creates a new default set. Then return to the SIMULATION menu.
Default traces are applied as follows:
| Domain | AC | DC | TR
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| | decibels, Phase | Magnitude | Magnitude
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To disable the auto-defaults system, go into the OPTIONS menu (from the FILE menu - AFT-F) and de-select DEFAULT-TRACES .
It may be instructive to create a set of defaults, and then click-on EDIT to see how they are specified.
Editing Traces
A trace is the line that appears on the output graph. A trace uses simulator variables to define it. A trace requires:
- A name
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A type (a pre-defined or a new user-defined type)
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An expression
To add a trace, press ADD. You will then be able to specify the name, type and expression of the trace. The types are the same as for the variables. An expression supports many operators and special functions, and may use any legal variable . All valid variables for the current circuit are listed.
To insert a variable into the expression, press INS.
To use a variable as the sole trace expression, click-on USE.
When done, press OK.
Recognised trace types
| Voltage | Type | Function | Scope | Current | Type | Function | Scope
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| VM | Voltage Magnitude | AC, TR, DC | | IM | Current Magnitude | AC, TR, DC
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| VP | Voltage Phase | AC | | IP | Current Phase | AC
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| VR | Voltage Real | AC | | IR | Current Real | AC
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| VI | Voltage Imaginary | AC | | II | Current Imaginary | AC
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| VDB | Voltage decibels | AC | | IDB | Current decibels | AC
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| VGD | Voltage Group Delay | AC | | IGD | Current Group Delay | AC
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The trace type affects the graphing legends and groupings.
If the type is not a recognised type (e.g. gain, ohms (Ω)) SUMO will create a new legend and display the trace in the same graph as other traces of the same type.
Trace Expressions
The expression itself can contain any variables as long as they are in the list. INS inserts the variable name into the expression. Operators and functions that are supported in the expression are the same as those permitted in the VALUE menu. See an earlier section of the manual for details.
- Example: Gain
Name: Voltage or current Gain
Type: dBR
Expr: "20 * LOG10 (VMP2 / VMP1)"
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Example: Return loss
Name: Rloss
Type: ohms
Expr:
The regular form of calculating return loss (The amount of power which is reflected back to the source from an incorrectly terminated line) is given by the following equation
RL = return loss = 10·log(|(Zin - Zload) / (Zin + Zload)|
so for a 50Ω load the equation to use is:
RL = return loss = 10·log(|(Zin - 50) / (Zin + 50)|)
where Zin = Vin/Iin
So if suitable PROBEs and METERs are found for Vin and Iin respectively, the following can be used in the TRACE menu:
10*LOG10(ABS((VMVIN/IMIIN-50) /(VMVIN/IMIIN+50)))
Tweaking SUMOS-FUSION ......
Clicking-on OPTIONS in the SIMULATION menu opens the simulator options menu. This menu allows you to set global switches and variables for the current simulator. All simulators have a variety of options to control accuracy and other aspects.
The options set are only for the current circuit, and do not apply generally. You have to set options as required for each circuit, otherwise the simulators built in default values will be used.
Each simulator has a separate options section within the circuit, so setting an option for the current simulator will not affect options of the same name if you switch to another simulator, even though the circuit is the same.
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