As we have mentioned, MODUA is basically a nodal circuit simulator. It also serves as the graphic display tool for the IE3D simulation result. It accepts circuit elements as black boxes, which are called modules.
Figure 2.4 The MODUA window.
There are 10 module types in MODUA: geometry file, parameter file, resistor, capacitor, inductor, mutual inductor, port, connection, short circuit and open circuit. The 10 module types are sub-divided into two groups: independent modules and dependent modules. Geometry files, parameter files, resistor, capacitor and inductor are independent modules. They can be defined anywhere at any time. Port, mutual inductor, connection, short circuit and open circuit are dependent modules. At the time the dependent modules are defined, they must be connected to the terminals of the independent modules. When an independent module is deleted, the dependent modules connected to this independent module will also be deleted.
In some sense, MODUA is a circuit simulator similar to the old Touchstone simulator from Agilent/EEsof. However, MODUA does not have a big library. Since it is implemented for the post processing for IE3D, it really does not need a big library. It accepts geometry modules from MGRID.
Therefore, you can build any structure elements on MGRID and import them into MODUA.
The basic configuration of an MODUA window is shown in Figure 2.4. It consists of seven menu
2-24
items: File, Edit, Element, Control, Process, View and Help. They are documented in Table 2.18 to Table 2.23.
Table 2.18 The important menu items in the File menu of MODUA.
Menu Item Explanation
Add Geometry Module
Add an IE3D geometry file (.geo) as a module on MODUA.
Add Parameter Module
Add an IE3D s-parameter file (in Touchstone format) as a module on MODUA. Original Touchstone file put port information in the file extension. It is not consistent because different port number creates a file with different file extension. For this reason, we use extension .sp for IE3D’s s-parameters. Also, we put the number of port into the .sp file as a comment. An example is a line
“! Nport = 2” in a 2-port s-parameters. MODUA will detect the number of ports
= 2 when this file is imported into MODUA.
Display Parameter Module
MODUA saves and reads files with .dsg extension. It carries the information how the elements are connected. The .dsg file does not carry the information of the s-parameters. However, we implement the feature “Display Parameter Module” here to allow a user to setup the .dsg file automatically from the .sp file. When a user selects this command, MODUA automatically create the .dsg project for the only .sp file module and get the data displayed assuming the .sp file is the only module for the .dsg file. This command is the simple way to
Save S-Parameters Save the current simulated s-parameters into a file.
Open Matrix File Open a file containing the RLC matrix elements (an IE3D specific format). For transmission line structure, RLC topology is in matrix forms. It is easier to manipulate the matrix than the SPICE netlist. A user can use the IE3D to model a small portion of a package structure and extract the RLC matrices. They can use the local RLC matrices to expand it into an overall RLC matrix using a spreadsheet application. Then, he can import the RLC matrices back to the IE3D and convert it into SPICE file.
Save Matrix File Save the transmission line RLC equivalent circuit into an IE3D specific matrix file.
Save SPICE File Save the transmission line RLC equivalent circuit into a SPICE net list file.
Import SPICE File Import a SPICE netlist file (containing R, L, C and K only) into the current design. This feature is very important on checking whether an equivalent circuit is working fine. For example, you use the RLC equivalent circuit feature in IE3D to extract the SPICE circuit. You do not know how good the equivalent circuit is. You can import it back to MODUA and do a simulation. Then, you can compare the simulation result of the equivalent circuit to the original s-parameters to find out the valid frequency range of the equivalent circuit. You can even fine-tune the SPICE model using the Process->Match Queue command.
Export SPICE File Export the current design (R, L, C, mutual inductor and short circuit only) into a SPICE net list file.
Merge Matrix Files This is a useful command for modeling large signal integrity (SI) structure. For example, we may have a lead frame with tens or hundreds of leads. If we break it into smaller size to simulate, the result may not be accurate for some leads on the edge of the size. The Merge Matrix File allows a user to merge the
2-25
extracted RLC circuits of the smaller sections in matrix form to get the complex RLC circuit in matrix form for the whole structure.
Save Excitation Save the result of the Process->Simulate and Find Excitation command. The saved file can be imported into MGRID in post processing mode to find the current and radiation patterns of a structure with lumped elements connected.
Save TLN Information Save the transmission line parameters into a text file.
Table 2.19 The menu items in the Edit menu of MODUA.
Menu Item Explanation
Select Module Set the input mode to select module mode. In select module mode, you can move the module by dragging it. You can use other menu items to control the modules. It is the default mode on MODUA.
Module Properties Display the module properties of the selected module. You can replace the selected R, L or C element with a different R, L or C element.
Rotate Module Rotate the direction of the module or the ports of the selected module.
Fix Module Fix the dropped module at the current location.
Delete Module Delete the selected modules.
Remove optimization variables from the selected R, L, C and mutual inductor elements.
Delete Dependent Modules
Delete all the dependent modules (connection, short circuit, open circuit, mutual inductor) of the design.
Set all RLCM as Optimization
Variables
Set the values of all the R, L, C and mutual inductor as optimization variables.
Remove RLCM Optimization
Variables
Set the values of all the R, L, C and mutual inductor as optimization variables.
Exit Status Exit the edit mode.
Table 2.20 The menu items in the Element menu of MODUA.
Menu Item Explanation
Port Create a port module. You need to connect the Port module to a terminal of an independent module. After you connect a port to a terminal of an independent module, you are still in the Element->Port mode for another port. In case you want to exit, you can select Element->Exit Element or click an empty spot and confirm the exit.
Define All Ports Create one or more port modules on the spare terminals of all independent modules. A spare terminal is a terminal without any connection.
Connection Create a Connection module. You need to connect the two terminals of the Connection module to two different terminals of independent modules. When you use a Connection module to connect two different terminals of independent modules, the two connected terminals will be of the same potential. After you finish connecting the terminals, MODUA will still be in the
>Connection mode for a new Connection element. You can select
Element->Exit Element or click at an empty spot and confirm the exit.
Short Circuit Create an idealized short circuit. The Short module needs to connect to a terminal of an independent module. After connection, MODUA will still be in Element->Short Circuit mode. Please understand that Short Circuit does not necessarily mean 0 potential on MODUA. If it is a single ended system, a Short circuit element does mean 0 potential. However, for differential system, a Short
2-26
circuit alone only means the return path of the element. When it is used in a differential system, please be careful not to share a Short circuit element between multiple independent terminals. If you use Connection elements to connect multiple independent terminals of differential elements together, it may result in nonphysical results. In fact, you need to use all dependent elements (Short, Open, Connection and Mutual Inductor) very carefully in a differential system.
Open Circuit Create an idealized open circuit. The Open module needs to connect to a terminal of an independent module. MODUA will remain in Element->Open Circuit mode for a new Open circuit element after you define one Open circuit element.
Termination Allow a user to build a resistor with one terminal short-circuited in one step. In fact, it is not an element of MODUA but a single step to create two elements (a Resistor and a Short circuit).
Resistor Create an idealized resistor. You can define the value of the resistor as an optimization variable.
Capacitor Create an idealized capacitor. You can define the value of the capacitor as an optimization variable.
Inductor Create an idealized inductor. You can define the value of the capacitor as an optimization variable.
Mutual Inductor Generate a mutual inductor. You can define the value of the mutual inductor as an optimization variable. A Mutual Inductor module is a dependent module. It must be defined between two inductors. Each pair of inductor can have only one single Mutual Inductor module. The Mutual Inductor takes value range in (-1, 1). You can control the sign of the mutual inductor by connecting to different terminals. Connecting the mutual inductor at the port 1 of each inductor is the same as connecting the mutual inductor at the port 2 of each inductor. When you connect the mutual inductor at the port 1 of one inductor and port 2 of the other inductor, it means that the value of the mutual inductor will have a sign change in the calculation.
Exit Element Exit from the defining element mode.
Table 2.21 The menu items in the Control menu of MODUA.
Menu Item Explanation
Frequencies Allow a user to define frequency points for a simulation. This command is redundant because this dialog is called for almost every process in the current MODUA.
Define Display Data Define the parameter items for listing.
Define Display Graph Define the parameter items for graph display.
Define Display Smith Chart
Define the parameter items for Smith Chart display.
Terminating Impedance
Allow the users to change the termination or normalization impedance of each port. By default, the normalization impedance is 50-ohms.
Change Excitation In displaying the result of the Process->Simulate and Find Excitation command, you can change the excitation and terminations of the ports. This feature is good for finding out the excitation and loading of antenna arrays or antennas with lumped elements, for current visualization and pattern calculation.
Display Toggle Toggle between displaying the design topology and displaying the s-parameters.
Table 2.22 The menu items in the Process menu of MODUA.
2-27
Menu Item Explanation
Simulate Perform a nodal simulation on the circuit topology of the design.
Update Results Check the .sp files and update its data to the MODUA simulation. This feature is very useful in monitoring an on-going simulation on the IE3D. You can select Display on the IE3D simulator dialog to display the results of an unfinished simulation. Then, you can use the Process->Update Results command on MODUA to update the more finished data points from time to time while IE3D is still running the simulation.
Simulate and Find Excitation
Perform a simulation on the design. After the simulation, it will display the power, voltage, current and load at each port. You can then select
Control->Change Excitation command to adjust the excitation and terminations. The result can be saved into a file by selecting File->Save Excitation command.
The saved excitation file (.ect) can then be imported into MGRID for displaying current distribution and calculating and radiation pattern of a structure with lumped elements.
Batch Simulate and Find Excitation
Allow a set of simulations on a design with an s-parameter file replaced for each simulation to yield a set of .ect files.
Find S-Parameters from Pi-Network
Allow a user to find the s-parameters of a frequency dependent Pi-network created using the Process->Pi-Network Equivalent command on MODUA.
Find S-Parameters from One-Port
Network
Allow a user to find the s-parameters of a frequency dependent 1-port circuit created using the Process->1-Port Equiv. Ckt command on MODUA.
Optimize Perform an optimization on the design. Please refer to the same menu item on MGRID for more information.
L-Equivalent Perform a simulation on the current design and solve for the matrix. L-equivalent is good for structure with dominant inductive effect. It is not as accurate as the LC-equivalent command discussed next. However, it reduces the number of elements.
C-Equivalent Perform a simulation on the current design and solve for the matrix. C-equivalent is good for structure with dominant capacitive effect. It is not as accurate as the LC-equivalent command discussed next. However, it reduces the number of elements.
LC - Equivalent Perform a simulation on the current design and solve for the LC-matrix of a design. It is more accurate then the L-Equivalent or the C-Equivalent commands. The results are not exact while it is frequency independent and compatible with SPICE if it is extracted at one single frequency.
General Lumped Equivalent Circuit
This is a new feature implemented in IE3D 12. After the implementation, the Pi-Network Equivalent and 1-Port Equiv Ckt commands become obsolete.
Pi-Network Equivalent Find the Pi-network equivalent circuit from a 2-port s-parameter file. The results are frequency dependent and exact. However, the Pi-network is frequency dependent and it is not compatible with SPICE.
1-Port Equiv. Ckt Find the 1-port equivalent circuit from a 1-port s-parameter file. The results are frequency dependent and exact. However, they are not compatible with SPICE.
Match Queue File This feature is useful in solving the frequency independent RLC equivalent circuit of specified topology of a design. The LC-Equivalent command is good only for coupled transmission line model. The model always assumes shunt C and R to ground and series L and R between input and output. They cannot be applied to any other structure such as series L and C. It is not realistic to build in different models for different structures. The Process->Match Queue File command allows a user to construct a topology based upon the elements on MODUA. MODUA will try to change the values of the RLCM elements to match the resulting s-parameters to the one saved in the Parameter File Queue.
2-28
For example, you have a complicated structure that cannot be fitted into the transmission line model. You simulate the structure to get the s-parameter file.
You put the file into then Parameter File Queue. Then, you build the RLCM model on MODUA. You set the appropriate RLCM modules as optimization variables. You define the appropriate frequency points and select the
Process->Match Queue File command. MODUA will try to fine tune the optimization variables and match the performance of the design to the parameter file in the queue. If it is successful, the RLCM topology will be a good SPICE representation to the parameter file in the queue. Sometimes, it may take a few runs before you can get a good result.
The Match Queue File command is also good for fine-tuning the result from LC-equivalent command. A user should understand that the LC-equivalent circuit is extracted at one single frequency point only. It works in a frequency range around where the extraction is performed. If you want to make it working in a wide frequency range, you can fine-tune the values of the LC-equivalent circuit based upon the s-parameter results. You may even need to change the LC-equivalent circuit and try to match the s-parameters in the queue for better result.
Back Simulation This feature makes the IE3D de-embedding even more flexible. One of its most important applications is in shifting reference plane for an IE3D simulation.
Shift reference plane is available on MGRID/IE3D for isolated ports.
Whenever you encounter a shift of reference plane, the IE3D will try to find the transmission line (TLN) parameters by simulating a short uniform line. Then, it will use the TLN parameters to do the shifting of reference plane. There are cases the shifting reference plane feature on MGRID/IE3D may not work well.
One case is that the ports are closely coupled together. When a few ports are coupled together, the TLN parameters are dependent on the excitation of the port parameters. Another case causing problem is a long distance reference plane shift. For example when we shift the reference plane by one wavelength, we need to change the phase of S21 by 720 degrees. If we introduce 0.1% error in calculating the wavelength, we will introduce 0.72-degree error in the phase of S21. If we shift the reference plane 10 wavelengths, the error in the phase of S21 may be 7.2 degrees. The problem in the magnitude of S21 is even more serious. This kind of error is actually understandable. However, you can get higher accuracy result by doing the following. You simulate your structure and simulate a 10-wavelength long TLN. Then, you use Process->Back Simulation command to remove the 10 wavelength long transmission line on the port. It is equivalent to the shifting reference plane on MGRID/IE3D.
However, it may be more accurate. In fact, the benefit of the Back Simulation goes beyond the shift of reference plane of uniform transmission lines. You can even use it to shift the reference plane of non-uniform transmission lines.
Separate S-Parameters This is a very powerful feature. It allows a user to separate an s-parameter file into two connected s-parameter files. It is very similar to the Back Simulation feature. However, this is a more general feature. It will be discussed in the manual.
Remove S-Parameters This is also a very powerful feature. It allows a user to remove the effect of coupled transmission lines on the ports. It is a command can replacing the Back Simulation. The Back Simulation can only remove the effect of isolated transmission lines on the ports.
Find Transmission Line Parameters
Solve for the characteristic impedance and other TLN parameters of the s-parameter file of a structure. The structure must be a uniform 2-port structure shorter than quarter wavelength. When you use this command to find the TLN
2-29
parameters from the 2-port s-parameters of a TLN, MODUA will prompt you for the physical length of the TLN. The characteristic impedance will be correctly calculated no matter what length value you enter. However, entering a value other than the actual one will certainly affect the propagation constant and effective dielectric constant.
Create TLN S-Parameters
Allow a user to create an s-parameter file for the frequency response of an ideal TLN based upon the electrical length, characteristic impedance and TLN parameters.
Curve Fitting and Interpolation
Curve-fitting the s-parameters with fine frequency detail based upon the
Curve-fitting the s-parameters with fine frequency detail based upon the