Configuration
System simulation settings.
blockType: SubSystem
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Path in the library: |
Description
Block Configuration sets the settings for modeling the circuit envelope. The block parameters define the RF and solver attributes. RF attributes include properties such as simulation frequency, harmonic order, envelope bandwidth, and thermal noise. Solver attributes include types of transient analysis, tolerances, and small-signal approximation.
The low-signal transient simulation performs a stationary nonlinear harmonic balance solution to determine the operating point for subsequent linear analysis of the transient. This option allows you to capture the correct spectral behavior of a small signal, which is influenced by large constant (over-carrier) signals.
Connect one unit Configuration to each topologically separate subsystem of the library RF Blockset. Each block Configuration defines the parameters of the connected library subsystem RF Blockset.
The block icon Configuration depends on the parameter value Simulate noise.
| The flag is selected Simulate noise | The checkbox is not checked Simulate noise |
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Ports
Conserving
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IN_1
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Input signal
electricity
Details
The input signal.
| Program usage name |
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Parameters
Noise
# Simulate noise — noise simulation
Details
Select this option to enable global noise modeling in library schematics. RF Blockset. When this checkbox is checked:
To disable noise modeling globally, uncheck this box.
| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
# Temperature, K — thermal noise temperature
Details
The global temperature of thermal noise, set as an integer in K.
| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
Spectrum
# Fundamental tones, Hz — the basic tones of the simulation frequency set
Details
The basic tones of the simulation frequency set, specified as a vector of positive integers in Hz.
| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
# Harmonic order — harmonic order for each fundamental tone
Details
The harmonic order for each fundamental tone, given as a vector of positive integers. You can also set this parameter as a scalar, then this value will be applied to each value. Fundamental tones, Hz.
| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
# Step size, s — time step for a fixed-step solver configuration
Details
The time step for the solver configuration with a fixed step, specified as a scalar in seconds. The inverse of the time step determines the simulation band of the signal envelope centered around each simulation frequency.
The time step of the circuit envelope simulation should be commensurate with the relative bandwidth of the signal, and not with the absolute value of the carrier frequency.
The default value is sufficient to simulate the envelope of signals with a bandwidth up to , or 1 MHz. Simulation accuracy is reduced when simulating near the maximum bandwidth. Reduce the step size to simulate signals with more bandwidth or improve accuracy.
The simulation speed is inversely proportional to the simulation step size. The smaller simulation step size corresponds to a wider envelope bandwidth and slower simulation.
In white noise simulation, the noise bandwidth for each simulation frequency is .
| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
Additional Info
Setup and complexity of the simulation
Details
The key parameters when setting up envelope modeling are the fundamental tone, harmonic order, and step size. To speed up the simulation, you can swap the simulation step size and the total number of simulation frequencies.
For example, if there are two large input signals with bandwidth 100 MHz each, with a central frequency 10 GHz and 10.1 GHz, respectively, it is possible to simulate these two signals using two separate fundamental tones. [10 10.1] GHz. Each tone has an order of harmonics 3 (total 25 simulation frequencies), and the simulation step size is 1/200 MHz = 5 Ns.
You can also configure the RF subsystem so that both signals are in the same simulated bandwidth with a central frequency. 10.05 GHz. In this case, the harmonic order is set equal. 3 (total 4 simulation frequency), and the simulation step size is 1/400 MHz = 2.5 hc. The latter configuration is faster because the number of simulation frequencies is less in 3 times, and the simulation step size is only in 2 times.
When setting up an envelope simulation, avoid overlapping envelopes. The thermal noise generated by the passive components is accounted for separately in each subband, which makes it possible to overlap individual envelopes.
Criteria for determining the simulation step size
Details
The simulation step size should be small enough to take into account the bandwidth of the signal and the in-band growth of the spectrum.
For example, a complex input signal has a sampling frequency equal to 10 MHz. The minimum time step required to simulate this signal is 1/20 MHz = 50 hc. You can use the oversampling coefficient from 4 before 8, which corresponds to the time step of the simulation from 25 ns before 12.5 hc. This makes it possible to detect the growth of the spectrum caused by nonlinear effects.
By default, the block Configuration allows you to automatically interpolate a base signal with a lower frequency into a radio frequency signal with a higher frequency. If you disable this property, it is recommended to use the same step size as the input signals. The input port resamples the input signal with the step size specified in the block Configuration. Using the same step size avoids the undesirable effects of spectrum overlap. It is best to resample the input signals before importing them into the library. RF Blockset using analog (continuous time) or digital (discrete time) interpolation filters.
Relative tolerance and absolute tolerance
Details
The circuit envelope solver in the library RF Blockset performs the solution of a set of nonlinear equations based on a set of system variables. These system variables are determined from the circuit topology and simulation frequencies. Relative tolerance and absolute tolerance are used to minimize the convergence error of system variables. The number of iterations used in each time step significantly affects the speed of solutions and the trade-off between accuracy and speed. This compromise is governed by the criterion of stopping iterations. This stopping criterion is based on three sub-criteria:
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Convergence to variable error:
where — system variables; — maximum iteration.
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Convergence to the remainder error:
where represents a part of , originating from - Oh branches.
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The maximum number of iterations.
Stop calculations if the first two sub-criteria are met or the last sub-criterion is met. If only one of the sub-criteria is met, an error is returned stating that the nonlinear solver did not work.