Simulating the Translated Netlist

Once your netlist is successfully translated into Advanced Design System, you can simulate your new circuit in ADS. This chapter discusses some of the details involved in circuit simulation and provides references to other sources. The example used in this chapter refers to the Transmission-Line Inverter design created in Including Models and Subcircuits.

Example SPICE Design

The following two example SPICE files make up a simple transmission line inverter. The first SPICE netlist (tline.sp) is a subcircuit.

*TRANSMISSION-LINE SUBCIRCUIT .SUBCKT TLINE 1 3 T1 1 2 3 4 Z0=50 TD=1.5NS T2 2 0 4 0 Z0=100 TD=1NS .ENDS TLINE .END

The next SPICE netlist (inverter.sp) includes additional components that complete the transmission line inverter design.

*TRANSMISSION-LINE INVERTER V1 1 0 PULSE 0 1 0 0.1NS 0.1NS 20NS 40NS R1 1 2 50 R2 4 0 50

The resultant file from the import process is called tline_inv.dsn . See Importing a Netlist File for more information.

Note Although tline_inv.dsn is a design translated from SPICE netlists, the simulation steps and concepts described in this chapter are directly applicable to Spectre imported designs.

Setting Up and Performing a Simulation

Setting up and performing a simulation in Advanced Design System requires several steps:

1. Opening the Schematic
2. Adding Simulation Components
3. Running the Simulation
4. Displaying the Results

Opening the Schematic

To open an existing schematic design:

1. Choose File > Open Design in the ADS Schematic window. The Open Design dialog box is displayed. You can use this dialog box to select the design you wish to simulate.
2. Choose the appropriate project from the Project drop-down list in the Open Design dialog box.
3. Click the appropriate design from the Designs list in the Open Design dialog box. (For this example the tline_inv.dsn file created in the Netlist Translator for SPICE manual will be used.)
4. Click OK to include the schematic in the ADS Schematic window.
   For more information on opening designs, refer to, "Opening an Existing Design" in the Schematic Capture and Layout manual.

Adding Simulation Components

After translating your netlist into Advanced Design System, you may need to add stimulus or simulation control components to your design. In the schematic window containing the design you want to simulate, select the appropriate simulation control elements from the component palette.
To add a simulation component to the tline_inv.dsn example:

1. Select the Simulation - Transient from the component palette. An instance of the TRANSIENT component is attached to your cursor (see The ADS Simulation-Transient Component).
2. Using your mouse, locate the component to an appropriate area on the schematic and click to place the component.
3. Click and edit the values of the StopTime and MaxTimeStep Tran parameters. For this example as follows:
   • StopTime=40 nsec
   • MaxTimeStep=.10 nsec

The ADS Simulation-Transient Component

For more information on using the Transient/Convolution Simulation component, refer to "Transient and Convolution Simulation".

Running the Simulation

Once you have added all of the necessary simulation components to your design, execute the simulation.
To run the simulation, choose Simulate > Simulate from the menu selection or click the Simulate button in the toolbar.

Simulation/Synthesis Message Window

The Simulation/Synthesis Message window appears whenever a simulator is launched and displays messages about the status of the current process, as well as warning messages. The window contains two information panels:

• Simulation/Synthesis Messages
• Status/Summary

Simulation/Synthesis Messages

The Simulation/Synthesis Messages portion of the window displays detailed messages about problems encountered during a simulation or synthesis, and where possible, what you can do to solve the problem.

Hint Watch for a message that prompts you to click to view the source of the problem. Clicking this message highlights the component(s) (in the Schematic window) causing the problem.

Status/Summary

The Status/Summary portion of the window displays a Simulation finished message, statistics such as how long the simulation or synthesis took, and the system resources used.

Viewing Simulation Status and Error Messages

When the simulation/synthesis is finished, you can save the displayed information to file or you can send it directly to the printer.

To save the currently displayed information to file with a default filename:

Choose File > Save and click OK. The default filename consists of the simulation process number (from the title bar of the window), with a prefix of the string sessloghpeesofsim and a file extension of .txt. The file is saved to the current project directory.

To save the currently displayed information to a file with a different filename:

Choose File > Save As. Supply a filename and click OK. The file is saved to the current project directory.

Note If you have changed projects during the current session, the file may be written to the initial project opened in this session.

To send the information directly to the printer:

1. If needed, choose File > Print Setup to establish the desired setup and click OK.
2. Choose File > Print. The displayed information is sent to the printer. For details on print setup, refer to "Printing and Plotting" in the "Schematic Capture and Layout".

For more information on performing a simulation, refer to "Simulation Basics" in Using Circuit Simulators.

Displaying the Results

After your simulation is complete, ADS automatically opens a Data Display window so that you can view your simulation results. You can also open a Data Display window to see the results of a simulation analysis by choosing Window > New Data Display from the Main or Schematic window. After a Data Display window is open, you can select an independent swept variable, select dependent measurements, scale the data, and add captions to your graph. Then you can print or plot the graph.

To view the results of the simulation in a plotted Data Display:

1. Choose the Rectangular Plot icon to drag and drop the plot frame in the Data Display window.
   The Plot Traces & Attributes dialog box appears.
   
2. Select the dataset to display from the Datasets and Equations drop-down list ( tline_inv for this example).
3. To define the traces for display on your plot, individually double-click the data ( netin , netout and vsource for this example) to add each item to the Traces field. Alternatively, you can select each item and then click the Add button.
4. Click OK in the Plot Traces & Attributes dialog box. The graph is displayed in the Data Display window. Choose View > View All in the Data Display window to enlarge the plot to fit the display window.

Transmission-Line Inverter Simulation Results

The preceeding illustration displays the simulation results for the Transmission-Line Inverter ( tline_inv ).

Analyzing and Comparing the Results

It is important to understand the results of your simulation to ensure that what you are looking at is not a result of your netlist translation, but rather the results of your circuit design. You can analyze your data by using the various tools available in the ADS Data Display, including a variety of plots, formats, markers and equations. For more information on working with data displays, refer to Data Display Basics.

After you understand your results, you can compare your ADS simulation results to your original HSpice simulation results. Ideally, you would like to compare your Spectre simulation data against your ADS simulation data using the same data file format; however, this is not always possible. There are two suggested methods that can be used to compare your simulation results:

1. Visually compare your ADS Data Display output to the visual display output you have available in your simulator tool. If you have the ability to output your data to an MDIF , Citifile or Touchstone file format, you can use the Data File Tool to convert your data to an ADS Dataset and view it in the ADS Data Display.
2. If your Spectre simulation results are in ASCII text format, you can convert your ADS dataset to MDIF , Citifile or Touchstone file format (ASCII text) and compare the data.
   For more information on the different file formats, refer to Converting to an ADS Dataset.

Note Remember that Spectre and HSpice simulators use different simulator technology from the ADS simulator; therefore, there may be incompatibilities between your file and the resultant ADS file that the translator was unable to accommodate. Refer to Troubleshooting for more information.

Converting to an ADS Dataset

Ideally, you would like to compare your simulation data against your ADS simulation data in the same data display format. One method of viewing your simulation data in an ADS Data Display is to convert your HSpice simulation data into a common file format that ADS has the ability to read. Once your data is in an accessible format, you can convert it to an ADS Dataset using the following table.

Data File Tool Supported File Types

File Type	File Extension	Description
ICCAP	.ds	Device under test (DUT), model (MDL), and setup (SET) files from the Agilent IC-CAP program. These files can contain Measured, Simulated, and/or Transformed data.
Touchstone File	.s*p	Touchstone data files are analog/RF circuit component data files that contain small-signal G-, H-, S-, Y-, or Z-network parameters described by frequency-dependent linear network parameters for 1-, 2-, 3-, or 4-port components. The 2-port component files can also contain frequency-dependent noise parameters. For more detailed information on the Touchstone file format, refer to the ADS Circuit Simulation manual.
Citifile	.citi	The Common Instrumentation Transfer and Interchange file __ (CITIfile) format is a standardized data format that is used for exchanging data between different computers and instruments. For more detailed information on the CITIfile format, refer to the ADS Circuit Simulation manual.
MDIF	.p2d, .s2d, .t2d	Measurement Data Interchange Format (MDIF) files are component data files for the .p2d, .s2d, and .t2d files.

For more information on the file formats listed above, refer to "Working with Data Files".

To use the Data File Tool to create an ADS dataset:

1. From the ADS Schematic window, choose Tools > Data File Tool. The dftool/mainWindow dialog box appears.
   
2. In the Data File Tool dialog box, click Read data file into dataset.
3. Under File format to read , click the appropriate file format (i.e. Touchstone , MDIF, Citifile, or ICCAP ).
4. Under Input file name , click Browse to navigate file paths and select your Spectre simulation result file.
5. In the Dataset Name field, enter the name of the HSpice dataset.
6. When all of the above settings are entered, click the Read File button.

For more information on reading files using the Data File Tool, refer to Reading and Writing Data Files.