DC Simulation Parameters
ADS provides access to DC simulation parameters enabling you to define aspects of the simulation listed in the following table:
| Tab Name | Description | For details, see... |
|---|---|---|
| Sweep | Defining sweep characteristics. | Setting Up a Sweep |
| Parameters | Provides options to set the following:
|
Defining Simulation Parameters |
| Output | Selectively save simulation data to a dataset. | For details, see Selectively Saving and Controlling Simulation Data. |
| Display | Control the visibility of simulation parameters on the schematic. | For details, see Displaying Simulation Parameters on the Schematic. |
| Additional parameters that you may find useful. | Additional Parameters |
Setting Up a Sweep
Setting up the sweep portion of the simulation consists of three basic parts:
- Identifying the parameter you want to sweep.
- Selecting the sweep type and setting the associated characteristics.
- Optionally, specifying a sweep plan.
To shorten simulation time in any parameter sweep, select a start point where convergence is easy, and vary the parameter gradually. When selecting a start point, if you find that convergence is easier at one end of a sweep and harder at the other, use the easy end as the start of the sweep. Varying the parameter gradually yields better estimates for the next simulation, and achieves convergence more rapidly than if the parameter is changed abruptly. However, too small a step can lead to a prohibitively large number of sweep points, so be careful. For additional information about parameter sweep techniques, see About Preparing Sweeps.
The following table describes the parameter details. Names listed in the Parameter Name column are used in netlists and on schematics.
| Setup Dialog Name | Parameter Name | Description | ||
|---|---|---|---|---|
| Parameter to sweep | SweepVar | The name of any defined parameter to be swept. | ||
| Parameter sweep - The sweep type and parameters. Disable Use sweep plan to set these parameters. | ||||
| Sweep Type | ||||
| Single point | Pt | Enables simulation at a specific value for the parameter. Specify the desired value in the Parameter field. | ||
| Linear | Enables sweeping a range of values based on a linear increment. Click Start/Stop to set start and stop values for the sweep, or Center/Span to set the center value and a span of the sweep. | |||
| Log | Enables sweeping a range of values based on a logarithmic increment. Click Start/Stop to set start and stop values for the sweep, or Center/Span to set the center value and the span of the sweep. | |||
| Start/Stop Start, Stop, Step-size, Pts/decade, Num. of pts. |
Start Stop Step Dec Lin |
Select the Start/Stop option to sweep based on start, stop, step-size and number of points. Step-size is Pts./decade for a Log sweep. - Start-the start point of a sweep - Stop-the stop point of a sweep - Step-size-the increments at which the sweep is conducted - Pts./decade-number of points per decade - Num. of pts.-the number of points over which sweep is conducted |
||
| Center/Span Center, Span, Step-size, Pts./decade, Num. of pts. |
Center Span Step Dec Lin |
Select the Center/Span option to sweep based on center and span, points per decade and number of points. Pts./decade is Step-size for a Linear sweep. - Center-the center point of a sweep - Span-the span of a sweep - Step-size-the increments at which the sweep is conducted - Pts./decade-number of points per decade - Num. of pts.-the number of points over which sweep is conducted |
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| Note: Changes to any of the Start, Stop, etc. fields causes the remaining fields to be recalculated automatically. | ||||
| Use sweep plan | SweepPlan | Enables use of an existing sweep plan component (SweepPlan). Select this option and enter the name of the plan or select it from the drop-down list. | ||
About Preparing Sweeps
In ADS, the DC simulation setup dialog enables you to sweep a parameter. You can sweep a parameter using the internal sweep or use the ParamSweep component for an external sweep. The internal parameter sweep is recommended over an external parameter sweep when only one parameter is swept. To improve the convergence process during such an internally swept DC bias simulation, the simulator uses the results from the previous sweep point as an initial guess for the next sweep point and employs a sophisticated arc-length algorithm. In many cases, this makes for a faster and more robust simulation than one done with an external ParamSweep component. The latter simulation simply repeats the DC simulation at each sweep point, with no arc-length continuation. When multiple parameters are swept, the internal parameter sweep can be employed for one parameter and an external parameter sweep must be used for the remainder of the parameters.
The results of the swept DC bias simulation are saved in a binary form in a temporary file. This file is used to post-process selected measurements. Because this file contains all of the results, new measurements can be specified and displayed without the need for a subsequent simulation.
Defining Simulation Parameters
Defining the simulation parameters consists of three basic parts:
- Specifying the desired level of detail in the simulation status summary.
- Specifying the amount of device operating-point information to save in ADS.
- Optionally, choosing to save all solutions to the dataset.
Note
Advanced simulation parameters are accessible with this group. However, as a result of the improvements made to the DC simulation algorithm, it is extremely unlikely that the default values need to be modified. You are strongly encouraged to leave the advanced parameters set to their default values. If you encounter a circuit for which a DC analysis does not converge using the default values, or you find it necessary to change the value of any of these parameters, please contact Agilent EEsof Technical Support. See Defining Advanced Simulation Parameters for details about these parameters.
Caution
In ADS, simulator parameters saved in ADS design files in previous releases are supported in later releases. The advanced simulation parameters saved prior to and opened in ADS 2005A are recognized and populated in the simulation setup dialog box. However, due to the improvement in robustness and speed of the default DC simulation algorithm the user-defined values are disabled, and factory-defined default values are used. Changing these default values is not recommended. However, if you find it necessary to restore the original user-defined values, you must manually enable Advanced Settings to restore them.
The following table describes the parameter details. Names listed in the Parameter Name column are used in netlists and on schematics.
| Setup Dialog Name | Parameter Name | Description | ||
|---|---|---|---|---|
| Levels - Enables you to set the level of detail in the simulation status report. | ||||
| Status level | StatusLevel | Prints simulation information in the Status/Summary part of the Message Window.
- 0 reports little or no information, depending on the simulation engine. - 1 and 2 yield more detail. - Use 3 and 4 sparingly since they increase process size and simulation times considerably. The type of information printed may include the sum of the current errors at each circuit node, whether convergence is achieved, resource usage, and where the dataset is saved. The amount and type of information depends on the status level value and the type of simulation. |
||
| Device operating point level | DevOpPtLevel | Options to save device operating-point information for most active devices and some linear devices in the circuit to the dataset. If this simulation performs more than one DC analysis (from multiple DC controllers), the device operating point data for all DC analyses will be saved, not just the last one. Default setting is None. | ||
| None | None (0) | No information is saved. | ||
| Brief | Brief (2) | Saves device currents, power, and some linearized device parameters. | ||
| Detailed | Detailed (4) | Saves the DC operating point values which include the device's currents, power, voltages, and linearized device parameters. | ||
| Output solutions | ||||
| Output solutions at all steps | OutputAllSolns | Instructs the simulator to save all solutions in the dataset. When the simulator is required to use points between steps in order to converge, the resulting information is stored and can subsequently be used for more detailed analysis. | ||
| Advanced | Click Advanced on the Parameters tab, and enable Advanced Settings to set these parameters. For parameter descriptions, see the following section, Defining Advanced Simulation Parameters. | |||
Defining Advanced Simulation Parameters
The stand-alone DC simulator's sole role is to do a DC analysis. All other simulators such as AC, S-parameter, transient, harmonic balance, and circuit envelope do an initial DC analysis as their first step. The advanced simulation parameters are used for controlling a stand-alone DC simulation. For information about setting DC convergence parameters for these analyses, see Setting Convergence Options.
The robustness and speed of the default DC analysis algorithm was significantly improved in ADS 2005A. All DC analyses with factory-default settings are expected to converge to the correct solution with near-optimal speed. This means that it is extremely unlikely that any of the following advanced simulation parameters must be altered:
| ConvMode | ArcMaxStep |
| MaxDeltaV | ArcLevelMaxStep |
| MaxIters | ArcMinValue |
| MaxStepRatio | ArcMaxValue |
| MaxShrinkage | LimitingMode |
The following table describes the parameter details. Names listed in the Parameter Name column are used in netlists and on schematics.
| Setup Dialog Name | Parameter Name | Description | ||
|---|---|---|---|---|
| Advanced Settings | Click Advanced Settings to set these parameters. | |||
| Max. Delta V | MaxDeltaV | Maximum change in node voltage per iteration. If no value is specified, the default value is four times the thermal voltage, or approximately 0.1 V. | ||
| Max. Iterations | MaxIters | Maximum number of iterations to be performed. The simulation will iterate until it converges, an error occurs, or this limit is reached. | ||
| Mode | ConvMode | Offers a choice between different convergence algorithms. Note that the convergence algorithm selected here applies to this DC simulation only. You can choose from these same convergence algorithms using the simulator options to apply them to all analyses performed for this design. | ||
| Auto sequence | 0 | Default convergence mode. Cycles through various algorithms and parameter values and has been optimized for both robustness and speed. Should converge for all circuits, and is therefore strongly recommended over all other convergence modes. | ||
| Newton-Raphson | 3 | Iterative process that terminates when the sum of the currents into each node equals zero at each node, and the node voltages converge. Used by other convergence modes. | ||
| Forward source-level sweep | 4 | Sets all DC sources to zero and then gradually sweeps them to their full values. The source steps are determined via homotopy/continuation methods. | ||
| Rshunt sweep | 5 | Inserts a small resistor from each node to ground and then sweeps this value to infinity. | ||
| Reverse source-level sweep | 6 | Rarely used, but available for those few cases where it is necessary. Similar to Forward source-level sweep, except in the reverse direction. Use Reverse source-level sweep when Forward source-level sweep returns an "out of bounds" error. This error indicates that there is a negative resistance in the circuit when all the DC sources are zero. This is a rare situation but can occur with ideal models of oscillators, such as those described by the van der Pol equation. | ||
| Hybrid solver | 7 | Combination of various algorithms. Starts with Forward source-level sweep with the source steps determined via heuristics. If this fails, Forward source-level sweep with the source steps determined via homotopy/ continuation methods is attempted. If this fails, Reverse source-level sweep with the source steps determined via homotopy/continuation methods is attempted. If this fails, Rshunt sweep is attempted. If this fails, Gmin relaxation, where a 1 Mohm resistor is inserted from each node to ground and then swept to infinity, is attempted. | ||
| Pseudo transient | 8 | Variant of the source stepping algorithm. Performs a transient simulation on a pseudo circuit derived from the original circuit. The transition from the zero solution to the final solution is of no interest in this analysis, so the truncation error is ignored and the timestep is taken as large as possible. After this pseudo transient analysis, a Newton-Raphson analysis is performed with the pseudo transient solution as the initial guess. If this fails, a Newton-Raphson analysis with Gmins of 1e-12 Siemens inserted from each node to ground is attempted. If this succeeds, the Gmins are removed and a Newton-Raphson analysis with the Gmin solution as the initial guess is attempted. | ||
| Arc Max Step | ArcMaxStep | Limits the maximum size of the arc-length step during arc-length continuation. During arc-length continuation, the arc-length is increased in steps. The step size is calculated automatically for each problem. However, if ArcMaxStep is specified and is nonzero, it will define an upper limit for the size of the arc-length step. The default is 0, meaning there is no upper limit for the arc-length step. | ||
| Arc Level Max Step | ArcLevelMaxStep | Limits the maximum arc-length step size for source-level continuation. The default is 0 which means there is no limit for the arc-length step. | ||
| Arc Min Value | ArcMinValue | Set relative to ArcMaxValue. ArcMinValue determines the lower limit that is allowed for the continuation parameter p during the simulation. During arc-length continuation, p can trace a complicated manifold and its value can vary non-monotonically. ArcMinValue specifies a lower bound for p such that if during the arc-length continuation p becomes smaller than ArcMinValue, the simulation is considered to have failed to converge. The default is pmin - delta, where delta is pmax - pmin, where pmin is the lower end of the parameter sweep and pmax is the upper end of the parameter sweep. | ||
| Arc Max Value | ArcMaxValue | Set relative to ArcMinValue. ArcMaxValue determines the upper limit that is allowed for the continuation parameter p during the simulation. During arc-length continuation, p can trace a complicated manifold and its value can vary non-monotonically. ArcMaxValue specifies an upper bound for p such that if during the arc-length continuation p becomes greater than ArcMaxValue, the simulation is considered to have failed to converge. The default is pmax + delta, where delta is pmax - pmin, where pmin is the lower end of the parameter sweep and pmax is the upper end of the parameter sweep. | ||
| Max Step Ratio | MaxStepRatio | Controls the maximum number of continuation steps. The default is 100. | ||
| Max Shrinkage | MaxShrinkage | Controls the minimum size of the arc-length step. The default is 1e-5. | ||
| Limiting Mode | LimitingMode | Sets the type of limiting done on the changes of nodes at each iteration. | ||
| Global Element Compression | 0 | Limits the changes at the nonlinear nodes with a log function at each iteration when the changes exceed the internally determined value. | ||
| Global Device-based Limiting | 1 | Performs limiting on the changes at each iteration for the nonlinear components. | ||
| Dynamic Element Compression | 2 | Limits the changes at the nonlinear nodes with a log function at each iteration when the changes exceed the internally determined value. | ||
| Dynamic Vector Compression | 3 | Limits the changes of all nodes with a log function at each iteration when the changes exceed the internally determined value. | ||
| Global Vector Compression | 4 | Limits the changes of all nodes with a log function at each iteration when the changes exceed the internally determined value. | ||
| Global Vector Scaling | 5 | Scales the changes of the node at each iteration with internally determined scale factor. | ||
| No Limiting | 6 | No limiting will be done on the changes of all the nodes at each iteration. | ||
Additional Parameters
The following table includes additional parameters that you may find useful.
| Setup Dialog Name | Parameter Name | Description | |
|---|---|---|---|
| Optimization | |||
| Compute Sensitivities Using Finite Difference | UseFiniteDiff | Perform sensitivity analysis optimization using the Finite Difference approximation method. This requires N+1 circuit simulations, where N is the number of optimization variables. To set this parameter in ADS, select the parameter name on the Display tab, then enter the value directly on the schematic. Allowed values: yes and no. | |
| Other | Use Other to enable access to hidden parameters, and assign values to them. The format isOther=HiddenParameter1=value1 HiddenParameter2=value2...Hidden parameters typically are used when troubleshooting convergence problems. To set this parameter in ADS, select the parameter name on the Display tab, then enter the value directly on the schematic. |
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| Restart | Restart |
Use Restart to control how an External DC Sweep picks an initial guess. Allowed values are 1 or 0. Restart=1 (the default value) instructs the External DC Sweep to treat each sweep point as an independent DC simulation. Restart=0 instructs the External DC Sweep to use the solution at each point as an initial guess for the next point. To perform an External DC Sweep, use a Parameter Sweep component. Restart has no effect on internal DC sweep (which is set from the Sweep tab of the DC simulation controller). Internal DC sweep is an arc-length continuation and by definition always uses the solution at the current point as an initial guess for the next simulation point. | |
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