Verilog-AMS Tutorials using SMASH from CMOSedu.com (Return)  

 

Tutorial 1 - Creation and setup of a basic circuit file.

 

1.     Create a folder named “Tutorials” on the desktop.

2.    Next, "Create A New Circuit" using the menu items FileàNew Circuit...  

3.    A window will open. Select Circuit File (.cir) from the drop down menu as seen below.  Name the project "Basic_Sim1" and then select the Tutorials folder created in Step 1 for the location of the circuit file.

http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_1.PNG

4.    The next window to open will be the circuit file.  This file will contain the main headers of all the component files you use as well as the top level of the circuit you build.  This file will also have the spice commands of the simulations you perform.  To get started lets add some basic header files.

5.    To add your library (aka header) files go to menu items SetupàLibrary Paths...

6.    Click the Add... button and add the Verilog-AMS (.vams) files you wish to use, and then click Ok.  (For this demo I save several component files in the folder so adding them to project would be easy)

 http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_2.PNG

7.    If you are successful you will see .LIB followed by the name of the files you added. The next step is to build a circuit.  You can accomplish this in two ways.  You can create a spice netlist in the current file and use the .LIB as references or you can create a separate file and “build” the circuit there.  For this tutorial we will do option 2 since it is the option you will use the majority of the time

8.    Select FILEàNEW to open a blank document.  From here you will build a circuit based on the library of components you added. 

9.    First you must include two more .vams files.  Type: `include “disciplines.vams” and `include “constants.vams”  These two include files various constants used when writing Verilog-AMS such as PI and electric charge.

10. Next you need to create a “module.”  This module is essentially a block where you will build your circuit.  Just as you would in a GUI based simulator you must define the parameters of your block.  First name your module in the following syntax:  module {module_name}; An example would be module basic_sim1_top;

11.  After you named your module you need to define the nodes of the system.  The next line you text should be: electrical {input/output parameter}; an example would be: electrical vin, vss; where vin and vss are nodes of the module.  (NOTE: typing electrical is crucial since it allows the nodes to behave with electrical characteristics.  If you neglect typing electrical then the nodes will create errors and not behave properly during simulation.)

12. Next we should define our ground (if one exists.)  In this tutorial I will treate vss as ground so I must also type: ground vss;  this makes ground the reference points for all electrical simulations later on.  This is almost always required since there is some ground within any circuitry.

 http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_3.PNG

13. Now we should define our components.  The syntax for define a component is: )  {Verilog_source_name}#(parameters)  component_name( passed nodes).  For example, in this tutorial I wish to define my voltage source I would type: VDC #(1) VIN(vin, vss);  If I were to check my “Vsource.vams” file I would see the names of various sources.

 http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_4.PNG

Based on the Vsource code I see that the VDC source has two parameters (p,n) so to use this component I must pass two parameters when I call it (vin, vss).  There is also a single parameter (dc = 2.0).  Therefore I need to pass a single value to represent the dc source value (#(1) means I pass 1 to the dc parameter).  If I neglected to pass a parameter then the default value would be used (2.0). Notice that the name VDC is used in the Vsource code and in our top module are the same. 

http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_DC.PNG

14. I now wish to create a resistor so I will do the same steps I performed to create a voltage source:  res1 #(1k) R1(vin, vss);  

http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_Res.PNG

You may notice that both components share the same nodes.  This means they are electrically connected together.  In this case my source is in series with my resistor.

15. Once you are finished adding all of your components, you need to “close” the module by typing: endmodule.  

16. Once completed now you need to save your module.  Select FILEàSAVE AS  and save the file as a .va file (verilog-A)

17. Now lets go back to our circuit file.  From here we can now add our module file to the circuit files so we can perform simulations.  Just like before we add module file the same way we added the .LIB files

 http://cmosedu.com/cmos1/verilog_ams/smash_tutorials/tutorial1/Tutorial1_op.PNG

18. Once you have added the module go to SETUPàTOP LEVEL INSTANCES.  A new window will open.  Scroll down until you find the name you’re your module (not the name of the file but the name you placed after the word “module”.)   NOTE: sometimes the module name is not present.  This means you need to reload your circuit file.  Save the circuit file, close the circuit file, open the circuit file again, and a dialog box should open prompting you to select the top level instance.  (if will be under the work expansion)

19. Your circuit is now complete.  To verify its operation you can run an .op (ANALSYSàOPERATING POINTàRUN) to check if the current and voltage levels match as expected. In the case of this tutorial we would expect that a 1V source in series with a 1k resistor would generate 1mA of current and 1mW of power.

 
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