I understand that the SimRF block library is divided into two main sections: Equivalent Baseband and Circuit Envelope. I would like to know more about these modeling methods, and the differences between them.
MATLAB: What are the differences between Equivalent Baseband and Circuit Envelope modeling, in SimRF 4.0 (R2013a)
RF Blockset
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There are several methods by which it may be possible to model a custom RF component in SimRF:
1) Use some combination of existing blocks:
Can the component be represented as some equivalent circuit that can be expressed in terms of the blocks in the SimRF library? If so, then the component can be modeled using some combination of the existing blocks.
The custom component model can be converted to a subsystem, or imported as a model reference or library block in some larger model. For a list of the blocks that are available in SimRF, please see the following links:
2) Represent the component using the RF Toolbox:
In RF Toolbox, it is possible to create data objects to represent circuit elements including amplifiers, mixers, S-parameter networks, and other generalized circuit elements. In general, S-parameters and amplifier/mixer data can be represented as RFDATA objects, and generalized circuit networks such as RLC networks can be represented as RFCKT objects. In turn, some of the blocks in the Equivalent Baseband Library offer the ability to import these RF Toolbox objects to define the block parameters.
If the component can be represented as an equivalent circuit in terms of the circuit elements available in the RF Toolbox, then the component can be created in RF Toolbox and imported into SimRF using the technique outlined above.
For more information on the RF Toolbox modeling objects, please see the following link:
3) Represent the component as equivalent S-parameters:
Is S-parameter data available for the component of interest? If so, then the data can be imported using one of the S-parameter blocks that are available in the SimRF library. For more information on the S-parameter blocks available in SimRF, please see the following links:
4) Interfacing SimRF with Simulink:
SimRF offers blocks that can be used to interface signals back and forth between Simulink and SimRF. Using these blocks, it may be possible to model an RF component as follows:
- Export the RF signal to the Simulink domain
- Use Simulink blocks to process the signal in some way
- Import the signal back into SimRF
Simulink has a very large variety of blocks available that may be used to process the signal in some desired manner. In addition, Simulink also has access to custom blocks such as S-functions that can be used to implement arbitrary functionality.
Simulink blocks cannot model circuit loading effects (because signals in Simulink propagate in one direction only). To model the loading effects of the custom element on the rest of the SimRF model, you can include input and output impedances before and after the Simulink blocks, as shown in the figure below:
Please use caution when importing/exporting signals between SimRF and Simulink. It is important to keep track of how SimRF signals map to the Simulink domain, and vice versa. The mapping is different for Equivalent Baseband and Circuit Envelope modeling. For more information, please see the following links:
How do I reduce the simulation time of my model in SimRF 4.0 (R2013a)?
I have a very large and complex SimRF model. When I simulate my model, it takes a very long time to run. I would like to know how I can speed up the execution time of my model.
Depending on the specifics of your model, there are several ways that it may be possible to reduce the simulation time:
1) If possible, use Equivalent Baseband (EBB) instead of Circuit Envelope (CE). EBB is faster than CE, although the tradeoff is less accuracy and modeling flexibility.
2) If you are using the Normal Simulink simulation mode, please consider switching to Accelerator or Rapid Accelerator mode. Accelerator mode is available for both EBB and CE models, while Rapid Accelerator mode is only available for EBB. For more information on the Accelerator/Rapid Accelerator modes, please see the following link:
3) Try changing the solver settings to see if that reduces the simulation time. In general, it is recommended to use the stiff solvers for physical modeling. If your model is CE, try changing the local solver setting. For more information on solvers in general and the local solvers in particular, please see the following links:
4) Try to simplify the model itself:
- Combine series and parallel components into equivalent single components.
- Derive the equivalent S-parameter representation for complex subsystems and replace the subsystem with an S-parameter block with these values.
- If the model is CE, try to reduce the number of simulated frequency harmonics/carriers in the SimRF Configuration block (trading some accuracy for higher speed).
5) If the model is CE, please consider upgrading to MATLAB release R2013a or later. The simulation speed of CE in R2013a was significantly improved relative to R2012b and earlier releases.
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