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Configuration

Specify system-wide parameters for circuit envelope analysis

Library

Utilities

Description

Use the Configuration block to set the model conditions for a circuit envelope simulation. The block parameters define a set of simulation frequencies, solver attributes, and thermal noise.

Connect one Configuration block to each topologically distinct SimRF™ subsystem. Each Configuration block defines the parameters of the connected SimRF subsystem. To see an example of the Configuration block in a model, enter simrfV2_noise in a MATLAB Command Window.

For an introduction to RF simulation, see Simulate High Frequency Components.

Dialog Box and Parameters

Automatically select fundamental tones and harmonic order

When this check box is selected, the block determines the Fundamental tones and Harmonic order parameters automatically when you update the model. Automatic selection does not always return the smallest possible set of simulation frequencies.

Clearing this check box enables you to manually set the Fundamental tones and Harmonic order parameters. A smaller set of simulation frequencies decreases simulation time and decreases memory requirements. However, a decrease in simulation frequencies can reduce accuracy.

Fundamental tones

When Automatically select fundamental tones and harmonic order is cleared, specify a vector of positive frequencies. These frequencies represent the fundamental tones [f1f2, …] of the set of simulation frequencies. See the Total simulation frequencies parameter for additional information.

Harmonic order

When Automatically select fundamental tones and harmonic order is cleared, specify the harmonic order [h1h2, …] of each fundamental tone. Each hi is a positive integer. You can specify a scalar that will be applied to each Fundamental tones parameter. See the Total simulation frequencies parameter for additional information.

Total simulation frequencies: Computed at simulation time

The block displays the number of simulation frequencies for a nonlinear model. For linear models, the actual number of frequencies are automatically optimized during simulation. Because the solver computes a solution to the network at each simulation frequency, computation time scales according to the size of this value.

Click View to open dialog box containing additional information about the simulation frequencies in your system. The Configuration: Explaining simulation frequencies dialog box lists tones and simulation frequencies. By clicking a listed simulation frequency, you can see which linear or multiple combinations of fundamental tones represent that frequency. From the dialog box, you can also plot the simulation frequencies on a number line.

The block parameters define a set of simulation frequencies as combinations of fundamental tones: [m*f1 + n*f2 + …]. In this case, represented as [f1,f2,…], and the integers m and n are bounded by the corresponding Harmonic order, |m| ≦ h1, |n| ≦ h2, etc. Only positive frequencies are considered.

For example, suppose you have a single fundamental tone f1 = 2 GHz and corresponding harmonic order h1 = 3. The set of simulation frequencies [ 0, f1, 2f1, 3f1] = [ 0GHz, 2GHz, 4GHz, 6GHz ].

As a second example, suppose you have a circuit with two fundamental tones [f1 = 2 GHz, f2 = 50 MHz] and corresponding harmonic orders h1 = h2 = 1. This setup results in five simulation frequencies with values [ 0, f2, f1-f2, f1, f1+f2].

The set of simulation frequencies must include all carrier frequencies specified in the SimRF subsystem such as the carrier frequencies inside Inport, Outport, and source blocks.

Normalize Carrier Power

When this option is selected, the carrier power is normalized such that the average power of the signal is:

In this case, the corresponding passband signal at ω is represented by the equation

where:

  • I(t) is the in-phase part of the carrier signal.

  • Q(t) is the quadrature part of the carrier signal.

  • fk are the carrier frequencies.

When this option is not selected, the carrier power is not normalized. In this case, the average power of the signal is:

In this case, the corresponding passband signal at ω represented by the equation

Note that 0 carrier frequency is a special case. Its passband representation is always I and average power I2

By default, the check box is selected.

Solver

Specify the fixed-step solver for the SimRF environment. When you are not sure which solver to use, set this parameter to auto. When manually choosing a solver, consider the following benefits and drawbacks:

  • The Backward Euler solver is able to simulate the largest class of systems and signals. Damping effects make this solver suitable for wideband simulation, but overall accuracy is low.

  • The Trapezoidal Rule solver is accurate for narrowband simulations. However, frequency warping and the lack of damping effects make this method inappropriate for most wideband simulations.

  • The NDF2 solver balances narrowband and wideband accuracy. This solver is suitable for situations where the frequency content of the signals in the system is unknown relative to the Nyquist rate.

By default, Solver is set to auto.

The SimRF solver is an extension of the Simscape™ local solver. For more information on the Simscape local solver, see the Solver Configuration block reference page.

Step size

Specify a time step h for fixed-step integration. The default value is 1e-6 s, which is sufficient for modeling envelope signals with bandwidths of up to 1/h, or 1 MHz by default. However, simulation accuracy is reduced when simulating close to the maximum bandwidth. Reduce the step size to model signals with a larger bandwidth, or improve accuracy.

When the noise is simulated, the noise bandwidth for each simulation frequency is equal to 1/h.

Simulate noise

Use this parameter to globally enable or disable noise modeling for SimRF blocks that support noise. When this check box is selected:

  • Amplifier and Mixer blocks use the value of their respective Noise figure (dB) parameters.

  • Amplifier and Mixer blocks simulate with thermal noise at the temperature specified by the Temperature parameter.

  • Resistor blocks model thermal noise using the Temperature parameters.

  • Noise blocks model a specified noise power as a voltage or current source.

Clearing this check box disables noise modeling in the SimRF environment. By default, this check box is selected.

Temperature

When Simulate noise is selected, specify a global noise temperature. The default value of this parameter is 290.0 K.

References

Motchenbacher, C.D. and J.A. Connely. Low Noise Electronic System Design. New York: John Wiley & Sons, 1993.

Rodrigues, Paulo J. C. Computer-Aided Analysis of Nonlinear Microwave Circuits. Norwood, MA: Artech House, Inc., 1998.

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