Define system simulation settings
RF Blockset / Circuit Envelope / Utilities
Use the Configuration block to set the model conditions for a circuit envelope simulation. The block parameter defines RF and solver attributes. The RF attributes include properties such as simulation frequencies, harmonic order, envelope bandwidth, and thermal noise. The solver attributes include transient analysis types, tolerances, and small signal approximation.
The small signal transient simulation performs a full nonlinear harmonic balance steady state solution to determine an operation point for a subsequent linear transient analysis. This option allows you to capture the right spectral behavior of a small signal affected by large constant (over carrier) signals.
Connect one Configuration block to each topologically distinct RF Blockset™ subsystem. Each Configuration block defines the parameters of the
connected RF Blockset subsystem. To see an example of the Configuration block in a model, enter
RFNoiseExample
in the MATLAB Command Window.
For an introduction to RF simulation, see Simulate High Frequency Components.
Configuration block mask icons are dynamic and show the current state of the applied noise parameter. This table shows you how the icons on this block vary based on the state of the Simulate noise parameter on the block.
Simulate noise: on  Simulate noise: off 



Automatically select fundamental tones and harmonic order
— Automatically select fundamental tones and harmonic orderon
(default)  off
Select this parameter to choose 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. This approach uses conservative number of simulation frequencies to capture the non linear behavior of the system.
To set the Fundamental tones and Harmonic order, clear this parameter. A smaller set of simulation frequencies decreases simulation time and decreases memory requirements. However, a decrease in simulation frequencies can reduce accuracy.
Fundamental tones
— Fundamental tones of set of simulation frequencyFundamental tones of a set of simulation frequencies, specified as a vector of positive integers in Hz.
To enable this parameter, clear Automatically select fundamental tones and harmonic order.
Harmonic order
— Harmonic order for each fundamental toneHarmonic order for each fundamental tone, specified as a vector of positive integer. You can also specify a scalar and this value is applied to each Fundamental tones.
To enable this parameter, clear Automatically select fundamental tones and harmonic order.
Total simulation frequencies: Computed at simulation time
— Displays number for simulation frequenciesThe block determines the simulation frequencies based on the fundamental tones and their respective harmonic order. The solver computes a solution to the network at each simulation frequency and the computation time scales according to the total number of simulation frequencies.
Combinations of fundamental tones determine the set of simulation frequencies: [m*f1 + n*f2 + …]. In this case, the fundamental tones are represented by [f_{s}1,f2,…], and the integers m and n are integers bounded by the corresponding Harmonic order, m ≦h1, n ≦h2, etc. Only positive frequencies are considered.
Click View to open the dialog box containing additional
information about the simulation frequencies in your system. The
Configuration
block displays the number of simulation frequencies
for a nonlinear model. For linear models, the actual number of frequencies are
automatically optimized during simulation.
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.
Consider a single fundamental tone f1 = 2 GHz and
corresponding harmonic order h1 = 3. The set of
simulation frequencies are: [0, f1, 2f1, 3f1] = [0GHz, 2 GHz, 4 GHz,
6GHz]
.
Consider 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, f1f2, f1,
f1+f2]
.
Consider a circuit with two fundamental tones [f1 = 2 GHz, f2 =
3GHz]
and corresponding harmonic orders h1 = 1
, and
h2 = 3
. This setup results in 11 simulation frequencies with
values: [0, f2, f1f2, f1, f1+f2, f1+2f2, 2f2, f1+3f2, f1+2f2, 3f2,
f1+3f2]
.
The set of simulation frequencies must include all carrier frequencies specified in the RF Blockset subsystem such as the carrier frequencies inside Inport, Outport, and source blocks.
To enable this parameter, select Automatically select fundamental tones and harmonic order. If you clear Automatically select fundamental tones and harmonic order, the option becomes, Total simulation frequencies: N/A: Fundamental tones undefined.
Step size
— Time step for fixed step solver configuration1e6
(default)  scalar in secondsTime step for fixed step solver configuration, specified as a scalar in seconds. The inverse of the time step determines the simulation bandwidth of the signal envelope centered around each simulation frequency.
The time step of a circuit envelope simulation should be commensurate to relative signal bandwidth and not to the absolute value of the carrier frequency.
The default (1e6s) is sufficient for modelling envelope signals with bandwidths of up to 1/h, or 1MHz. 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.
The simulation speed is inversely proportional to the simulation step size. A smaller simulation step size corresponds to a wider envelope bandwidth and to a slower simulation.
When the white noise is simulated, the noise bandwidth for each simulation frequency is equal to 1/h.
Envelope bandwidth
— Maximum simulated envelope bandwidth1 MHz
(default)  scalar in HzMaximum simulated envelope bandwidth, returned as a scalar in Hz. Configuration block automatically calculates this value using the Step size parameter. The formula used is: $$bandwidth=\frac{1}{(step\text{\hspace{0.05em}}\text{\hspace{0.17em}}size)}$$.
Simulate noise
— Globally enable or disable noise modelingon
(default)  off
Select this parameter to globally enable noise modeling in RF Blockset circuits. 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.
To disable noise modeling globally, clear this parameter.
Use default random number generator
— Default pseudorandom noise stream for RF Blockset sourceson
(default)  off
Select this parameter to retain the default pseudo random noise stream for RF Blockset sources. Clear this option to specify an independent pseudo random number stream for the RF Blockset topological subsystem and determine the seed of the noise stream.
To expose this parameter, select Simulate noise.
Noise seed
— Seed of the independent pseudo random number stream0
(default)  scalar positive integerSeed of the independent pseudo random number stream, specified as a scalar positive integer.
To expose this parameter, clear Use default random number generator.
Temperature
— Global noise temperature290.0
K
 scalar integer in kelvinGlobal noise temperature, specified as a scalar integer in kelvin.
Samples per frame
— Number of samples in each channel of input signal to Inport
block1
 positive scalar integerNumber of samples in each channel of input signal to Inport block, specified as a positive scalar integer less than or equal to
1024. A channel corresponds to an input frequency in the Inport
block.
Note
The recommended maximum number of samples per frame are 1024.
Normalize Carrier Power
— Normalize power of carrier signalon
(default)  off
Select this option to normalize the carrier power such that the average power of the signal is:
$${I}^{2}+\text{\hspace{0.17em}}\text{\hspace{0.17em}}{Q}^{2}$$
In this case, the equation gives the corresponding passband signal at ω:
$${s}_{k}(t)=I(t)\sqrt{2}\mathrm{cos}(2\pi {f}_{k}t)\text{\hspace{0.17em}}\text{\hspace{0.17em}}Q(t)\sqrt{2}\mathrm{sin}(2\pi {f}_{k}t)$$
where:
I(t) is the inphase part of the carrier signal.
Q(t) is the quadrature part of the carrier signal.
f_{k} are the carrier frequencies.
Clear this option so the average power of the carrier signal is:
$$\frac{{I}^{2}\text{\hspace{0.17em}}+\text{\hspace{0.17em}}\text{\hspace{0.17em}}{Q}^{2}}{2}$$
In this case, the corresponding passband signal at ω represented by the equation
$${s}_{k}(t)=I(t)\mathrm{cos}(2\pi {f}_{k}t)\text{\hspace{0.17em}}\text{\hspace{0.17em}}Q(t)\mathrm{sin}(2\pi {f}_{k}t)$$
0 carrier frequency is a special case. Its passband representation is always I and average power I^{2}
Enable input interpolation filter
— Automatic interpolation of lower rate baseband signal to higher rate RF signalSelect this option to enable input interpolation filter to up sample the input signal rates to fit sample rate of the RF solver. You can now directly use baseband communication signals using a lower sample rate in a wider band circuit. This filter introduces a delay in the RF signal. Filter delay (in samples) shows the delay introduced after you simulate the model.
Note
When you enable this filter,
The RFtobaseband sample rate ratio must be 2, 4, 6, or 8.
The RF Blockset model can have only one Inport block.
Transient analysis
— Fixedstep solver of RF Blockset environmentAuto
(default)  NDF2
 Trapezoidal Rule
 Backward Euler
Fixedstep solver of RF Blockset environment, specified as one of the following:
Auto
: Set this parameter
to Auto
, when you are not sure which solver
to use.
NDF2
: Set this parameter
to NDF2
to balance 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.
Trapezoidal Rule
: Set this
parameter to Trapezoidal Rule
for narrowband
simulations. Frequency warping and the lack of damping effects make
this method inappropriate for most wideband simulations.
Backward Euler
: Set this
parameter to Backward Euler
to simulate
the largest class of systems and signals. Damping effects make this
solver suitable for wideband simulation, but overall accuracy is low.
The RF Blockset solver is an extension of the Simscape™ local solver. For more information on the Simscape local solver, see the Solver Configuration block reference page.
Approximate transient as small signal
— Choose small subset of frequencies for transient small signal analysisSelect this option to choose a small subset of frequencies for transient small signal analysis.
Use all steadystate simulation frequencies for small signal analysis
— Choose all steadystate simulation frequenciesSelect this option to choose all steadystate simulation frequencies. Clear this option to specify the frequencies for small signal transient simulation.
To expose this parameter, check Approximate transient as small signal.
Small signal frequencies
— Frequencies for small signal transient simulationFrequencies for small signal transient simulation, specified as a scalar or vector. The frequencies specified are contained in the entire set of simulation frequencies determined from Fundamental tones and Harmonic order in the Main tab.
The default values in this box and the corresponding units are not constants. The values depend on the state of the configuration dialog box when Use all steadystate simulation frequencies for small signal analysis is first cleared.
To expose this parameter, clear Use all steadystate simulation frequencies for small signal analysis.
Populate Frequencies
— Tool to choose small signal transient frequenciesTool to choose small signal transient frequencies to populate Small signal frequencies. The selected frequencies are a subset of the simulation frequencies determined from Fundamental tones and Harmonic order inputs in the Main tab. The entire set of simulation frequencies are given in the combo box on the righthand side of the dialog box and the selected frequencies are highlighted. You can select by directly choosing the frequencies in the selection box, or by choosing the desired tones and harmonic order in the Small signal selection panel and pressing Select. The Tones(Hz) and Harmonic order values in the combo boxes are also populated using Fundamental tones and Harmonic order inputs in the Main tab.
To expose this parameter, clear Use all steadystate simulation frequencies for small signal analysis.
Relative tolerance
— Relative newton tolerance for system variables1e3
(default)  real positive finite scalarRelative newton tolerance for system variables, specified as a real positive finite scalar.
Absolute tolerance
— Absolute newton tolerance for system variables1e6
(default)  real positive finite scalarAbsolute newton tolerance for system variables, specified as a real positive finite scalar.
Maximum iterations
— Number iterations required for convergence10
(default)  real positive integer scalarNumber iterations required for convergence, specified as a real positive integer scalar.
Error estimation
— Check for error of convergence in system variables2norm over all variables
(default)  Each variable separately
Check for error of convergence in system variables, specified as:
2norm over all variables
: Use
this option to calculate the 2norm of all the state variables and
then check the error in convergence of state variables.
Each variable separately
: Use this
option to check the error in convergence of each variable separately.
Restore Default Settings
— Restore newton solver to default valuesRestore newton solver to default values, specified as a button.
The key parameters in setting up a Circuit Envelope simulation are the fundamental tones, the harmonic order, and the step size. To speed up simulation, you can trade off the simulation step size and the total number of simulation frequencies.
For example, suppose that you have two large inputs signals each with 100 MHz bandwidth, centered around 10 GHz, and 10.1 GHz respectively. You can simulate the two signals using two separate fundamental tones [10 10.1] GHz. Each tone has a harmonic order of 3 (for a total of 25 simulation frequencies), and a simulation step size equal to 1/200MHz = 5 ns.
You could also set up the RF subsystem so that both of the signals are within the same simulation bandwidth centered around 10.05 GHz. In this case, you set the harmonic order equal to 3 (for a total of 4 simulation frequencies), and a simulation step size equal to 1/400MHz = 2.5 ns. The latter configuration is faster as the number of simulation frequencies is smaller by a factor 3, and the simulation step size is only smaller by a factor 2.
When setting up a circuit envelope simulation, avoid overlapping envelopes. The thermal noise generated by passive components are accounted for separately in each subband thus allowing for overlap of separate envelopes.
The simulation step size must be small enough to capture the signal bandwidth and inband spectral regrowth.
For example, your complex input Simulink signal has a sample frequency equal to 10 MHz. The minimum time step required to simulate this signal is 1/20 MHz = 50 ns. You can use an oversampling factor from 4 through 8, corresponding to a simulation time step between 25 ns and 12.5 ns. This captures the spectral regrowth caused by nonlinear effects.
By default, the configuration block allows automatic interpolation of lower rate baseband signal to higher rate RF signal. If you disable this property, it is recommended that you use the same step size as the input Simulink signals. The input port resamples the input signal with the step size specified in the Configuration block. Using the same step size avoids undesired aliasing effects. It is best to resample the Simulink signals before importing them in RF Blockset using either analog (continuous time) or digital (discrete time) interpolation filters.
Circuit envelope solver in the RF Blockset is a solving a set of nonlinear equations from a set of system variables. These system variables are derived from the circuit topology and simulation frequencies. Relative tolerance and absolute tolerance are used to keep the error in convergence of the system variables to minimum. The number of iterations used at each time step dramatically affects the speed of the solutions and the tradeoff between accuracy and speed. The tradeoff is governed by the stopping criterion for the iterations. This stopping criterion is based on 3 sub criteria:
Variable error convergence:
$$\left\Delta X\right<\mathrm{Re}lTol.\underset{t}{\mathrm{max}}(\leftX\right)+AbsTo{l}_{x}$$
where:
X System variables
t maximum iterations.
Residue error convergence:
$$\leftF(X)\right<\mathrm{Re}lTol.\underset{t,n}{\mathrm{max}}(\left{F}_{n}(X)\right+AbsTo{l}_{F}$$
where:
F_{n}(X) represents a part of F(X) coming from the nth branch.
Maximum number of iterations.
Stop the calculations if the first two sub criteria are filled or the last sub criterion is filled. If only one of the subcriteria is filled, error out that the ' nonlinear solver failed'.
Behavior changed in R2021b
Starting in R2021b, the Configuration block icon is now updated. The block icons are now dynamic and show the current state of the noise parameter.
When you open a model created before R2021b containing a Configuration block, the software replaces the block icon with the R2021b version.
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