SIwave: Everything you need to know about the Resonant Mode Solver
SIwave is a tool designed for power integrity and signal integrity analysis. Today, we focus on the Resonant Mode Solver, which is crucial for identifying optimal locations for coupling capacitors in power planes.
Purpose of Resonance Calculations
- Identify the best location to place coupling capacitors in power planes.
- Determine the size of the power plane based on expected maximum current and allowed maximum voltage drop.
- Address the lack of sufficient capacitance to maintain low impedance across a broadband spectrum.
Key Features of SIwave
- Imports various CAD file types: ODB, IPC, EDB, DXF, and GDSI.
- Includes information such as material, stackup, dimensions, and nets.
- Begins any process by selecting the appropriate solver.
Using the Resonant Mode Solver
- Select the solver to generate a dialog box for inputting necessary parameters.
- Enter the minimum and maximum frequency to search for resonance within the design.
- Specify solver options for accuracy and speed.
- Launch the solver to begin calculations.
Understanding Resonance and Impedance
Resonance is defined as the frequency at which impedance is very high. In practical terms, at this frequency, the power plane behaves like a perfect antenna, radiating energy and accepting external signals, which can lead to system inefficiencies.
Analyzing Results
After running the solver, view the results to identify resonant frequencies and their characteristics:
- Real resonant frequency indicates the actual resonance point.
- Imaginary part represents losses or damping factor.
- Wave number (K) is calculated as frequency multiplied by a constant factor (2π/speed of light).
- Q factor indicates the sharpness of the resonance.
Practical Application of Results
To suppress resonance, place decoupling capacitors at identified locations, particularly where red spots appear in phase animations. This helps in reducing impedance peaks and improving system performance.
Additional Considerations
- Perform phase animation to understand resonance behavior.
- Use linear scaling for applications unless otherwise required.
- Monitor and adjust the placement of decoupling capacitors as needed.
Conclusion
The Resonant Mode Solver in SIwave provides valuable insights into power plane behavior, allowing for targeted improvements in system design through strategic placement of decoupling capacitors. By analyzing resonance and impedance, engineers can enhance the performance and reliability of electronic systems.
SI Wave: Everything you need to know about the Resonant Mode solver (HD) SI Wave is a power integrity and signal integrity tool. Today, we'll focus on the Resonant Mode solver, which computes resonant modes.
The main reason for performing resonance calculations is to identify the best location to place decoupling caps in power planes. The size of the power plane is determined by the expected maximum current and allowed maximum voltage drop.
However, even the best design may not have enough capacitance to keep the impedance low for a broadband spectrum. Power planes need decoupling caps to extend their bandwidth beyond the spectrum derived from current pulses. SI Wave can import various CAD files, such as ODB, IPC, EDB, DXF, and GDSI.
It imports all relevant information, including the material, stackup, dimensions, materials, and nets. When using any process in SI Wave, such as DC, PI, or signal integrity solvers, the user must first select the solver.
Once a solver has been chosen, SI Wave generates a dialog box that looks like a form. The user must check and fill in the necessary information.
For example, if you excite a computer as if it were a remote, you will see a simple dialog box requiring the minimum and maximum frequency, the frequency range for resonance search, the number of resonances, and the dissemination name.
You can also specify the solver's accuracy: optimal speed, optimum accuracy, or a balanced approach. Now, let's explore what happens if we do not have any decoupling caps in our model. From the PI analysis, we can plot Z11, which is important when solving a power plane.
By adding the equivalent circuit of the VRM and reading the impedance from the load side, we can study the power plane more accurately. In this example, we see a significant resonance at 206 MHz on the 1.2-volt power plane. We would like to extend our Z bandwidth beyond this value.
To do this, we will add decoupling caps at the right locations, with the correct values and quantities. The Resonant Mode solver will help determine where to place the decoupling caps.
After the solver is done, we can view the results, which include a list of all resonances in the PCB within the band of interest. The real part represents the resonant frequency, while the imaginary part stands for the losses or damping factor of the resonance.
The Q factor represents how sharp the resonance is. To determine where each resonance exists, you must display the field between two layers. In this case, we select the VCC and ground layers. After computing, you will see a list of 23 different plots, each representing one of the resonances.
By going through them one by one, you can identify where each resonance exists. Now, let's focus on the VCC with the ground, as that's where our power plane of interest is. By hiding the structure and displaying the field, we can see the resonance on the 3.3-volt power plane.
We would like to suppress this resonance by adding decoupling caps at the right places. After adding decoupling caps, we can look at the results of the Z11 plot. We have suppressed the resonance from 21 to 0.122, achieving our goal.
However, resonances may still be present, so it's essential to run the resonance solver and look at the fields one by one to ensure the right resonance has been suppressed.
