Genesys 2012 Tutorial 2 - Using Momentum Analysis for Microwave Planar Circuits: Circuit and EM Co-Simulation

Transcription

1 Genesys 2012 Tutorial 2 - Using Momentum Analysis for Microwave Planar Circuits: Circuit and EM Co-Simulation Here we demonstrate the process of running circuit and EM (electromagnetic) co-simulation. The electromagnetic interaction between the metallic interconnections on the PCB can be cast into a Y (admittance) matrix. The terminals on the Y matrix correspond to the metallic pads where we attach components or stimulus, these terminals are called ports here. We will use a simple Wilkinson Power Combiner/Divider to illustrate. We will treat the Wilkinson as a power combiner. Table 1 shows the important parameters. Center Frequency 3500 MHz Substrate Rogers R4350 Thickness of Substrate 30 mils Copper Foil Thickness 0.5 Ounce/square feet Impedance 50 Ohm Table 1 Parameters of the Wilkinson Power Combiner. Using microstrip transmission line synthesis tools, we can work out the required trace width for characteristic impedance Z c = 50 and Z c = 2 Z o = This is shown in Table 2. Characteristic Impedance Approximate Trace Width Unit mils mils Table 2 Required microstrip line trace width. As usual we invoke Genesys software and create a new workspace. We add a new design, in the form of a new layout WC1. We create the layout shown in Figure 1 (assuming the reader is already familiar with using the Genesys layout tools). Input 1 (Port 1) Footprint for 0402 size 100Ω resistor 50Ω trace Output (Port 2) 70.71Ω trace Input 2 (Port 3) Figure 1 The Wilkinson power combiner designed for operation near 3500 MHz. 1

2 Figure 2 shows the following commands to add the various geometrical shapes and objects into the design. Note that in Figure 2 we only construct the metallic structures. Figure 2 Commands to create the layout. In Figure 2 we also insert two Internal Ports (Port 4 and 5) on the center of the footprint pads for the 100Ω resistor. Figure 3 illustrate the setup of Port 4 and 5. Port 1, 2 and 3 remain as Normal Ports. For Normal Port during the solution for EM fields, the solver engine will automatically extend the length of the interconnection connected to the port to reduce the effect of evanescent mode due to the discontinuity at the port/trace interface. The extension length varies with the frequency for the EM field solution. 2

3 Trace will be extend to the left of Port 1 during solution process Port type selection Figure 3 Changing Port 4 and Port 5 to Internal Ports. Also the extension direction of Normal Port is shown for Port 1. Once the layout is complete, we insert a EM solver using MoM (Method-of-Moment) approached, called Momentum Analysis into our workspace, and assign the layout WC1 to the analysis. This is shown in Figure 4. As we span from 1 to 6 GHz, we set the Adaptive Frequency Sampling (AFS) to 50 frequency points. For frequency where the data changes less the frequency interval will be larger, and vice versa. The result of the Momentum Analysis is an admittance matrix of the form below: I1 y11 y12 y13 y14 y15 V1 I 2 y21 y22 y23 y24 y25 V2 I = 3 y31 y32 y33 y34 y35 V3 I 4 y41 y42 y43 y44 y45v4 I 5 y51 y52 y53 y54 y55 V5 Where I 1, I 2 etc. are the port current phasors and V 1, V 2 etc. are the port voltage phasors. 3

4 Figure 4 The Momentum Analysis setup. After the Momentum Analysis setup is done we run the analysis. Figure 5 shows the screen shot of the result. The elements of the Y matrix are stored in the array Y raw. 4

5 Figure 5 The Momentum Analysis result for Y raw. The Y matrix Y raw can be assign a special symbol, which contains 5 ports (actually there are 6 ports, the sixth port is grounded). To do this we invoke the Create Co-Simulation command by rightclicking the Momentum Analysis as shown in Figure 6. Once done you should see the Momentum3_Cosim (assuming we call our Momentum Analysis Momentum3) element on the file browser in Genesys, see Figure 7. We can create a new schematic, then drag-and-drop Momentum3_Cosim into the schematic as illustrated in Figure 7. 5

6 Figure 6 Generating a co-simulation component from the Momentum Analysis data. Figure 7 The Co-simulation component, and after inserting into a schematic. 6

7 We built up the schematic as shown in Figure 8, and assign to a Linear Analysis. Thus by now it is clear that the Co-simulation component forms a interconnection matrix that connects the input and output ports, and any discrete components together. This interconnection matrix accounts for the EM interaction of the conductors on the PCB. Observe that the Start and Stop frequencies of the Linear Analysis should match the Momentum Analysis. The simulated result is finally shown in Figure 9. Note that the simulated result shows the actual operating frequency is slightly higher than 3500 MHz. Figure 8 After connecting up the Co-simulation component with Input/Output stimulus and discrete component. 7

8 Figure 9 The final result, after performing Linear Analysis on the Wilkinson Power Combiner. Figure 10 The actual Wilkinson Power Combiner in action in a microwave circuit. 8