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Simulate a Passband Signal in Simulink Software |

This example shows how to use SimRF™ circuit envelope simulation to simulate high frequency components while reducing simulation time.

The model, `ex_simrf_tut_passband`, shows how
to modulate a real passband signal with in-phase and quadrature components.

To open this model, at MATLAB^{®} command line, enter:

addpath(fullfile(docroot,'toolbox','simrf','examples')) ex_simrf_tut_passband

The system specifies a real passband signal *x*(*t*)
according to the formula

where:

*I*(*t*) is the in-phase part of the modulating signal, equal to 3 in this example, modeled by the Constant block labeled In-phase modulation.*Q*(*t*) is the quadrature part of the modulating, equal to 4 in this example, modeled by the Constant block labeled Quadrature modulation.*f*is the carrier frequency, equal to 1 GHz in this example._{c}

Running the model produces the following output on the scope.

The output signal at the Real Passband Scope has a magnitude
of 5 and a phase shift of `atan2d(3,-4)`, or about
143°.

In the Configuration Parameters dialog box, the **Fixed-step
size (fundamental sample time)** parameter has been set to `1/16*1e-9`.
This value is on the order of the wavelength of the carrier. The simulation
takes a total of 81 samples — 16 per cycle.

The model, `ex_simrf_tut_compare`, shows how
to compare passband and baseband signals. This section builds on the
results of the previous section, Simulate a Passband Signal in Simulink Software.

To open this model, at MATLAB command line, enter:

addpath(fullfile(docroot,'toolbox','simrf','examples')) ex_simrf_tut_compare

The system simulates a real passband signal as the real part of a complex passband signal according to the formula

where:

*I*(*t*) +*jQ*(*t*) is the complex-valued modulation, equal to 3 + 4*j*.*f*is the angular frequency, equal to 1 GHz._{c}

Contrary to the Simulink^{®} passband implementation
in the previous section, the complex baseband signal driving the SimRF system
does not include the carrier. Instead, the SimRF environment
handles the carrier analytically. The carrier appears in four different
blocks in the SimRF environment:

In the Inport block, the

**Carrier frequencies**parameter defines the carrier frequencies of the modulations entering from outside the SimRF environment. In this example, there is only one input signal, and only one carrier (1 GHz, specified as`1e9``Hz`).In the Outport block, the

**Carrier frequencies**parameter specifies the signal on the`1e9``Hz`carrier (1 GHz) as Simulink signals. These signals appear at the I and Q ports. The**Output**parameter is set to`Real Passband`, so this signal represents a real passband signal on the 1-GHz carrier.In the block labeled SimRF Outport1 block, also an Outport block, the

**Carrier frequencies**parameter specifies the signal outputted on the`1e9``Hz`carrier (1 GHz) as Simulink signals. These signals appear at the I and Q ports. The**Output**parameter is set to`In-phase and Quadrature Baseband`, so these signals represent the in-phase and quadrature modulations of the signal on the 1-GHz carrier.In the Configuration block, the

**Carrier frequencies**parameter specifies all of the carriers to be modeled in the SimRF circuit envelope simulation environment. In this example, only one carrier is specified. For more options, refer to Configuration block.

Running the model produces the following output on the scopes.

The Real Passband Scope displays the same output as the example in the previous section, Simulate a Passband Signal in Simulink Software. The signal has a magnitude of 5 and a phase shift consistent with the specified in-phase and quadrature amplitudes.

The 1-GHz carrier itself does not appear in the output. The results correspond to the real and imaginary parts of the Complex modulation at the input of the system. They also correspond to the In-phase modulation and Quadrature modulation blocks in Simulate a Passband Signal in Simulink Software.

In the Configuration Parameters dialog box, the **Fixed-step
size (fundamental sample time)** parameter has been set to `1/16*1e-9`.
This value is on the order of the wavelength of the carrier. The simulation
takes a total of 81 samples — 16 per cycle.

The model, `ex_simrf_tut_envelope`, shows how
to simulate the envelope of a sine wave using SimRF blocks. This
section builds on the results of the previous section, Compare Passband and Baseband Signals in SimRF Software.

To open this model, at MATLAB command line, enter:

addpath(fullfile(docroot,'toolbox','simrf','examples')) ex_simrf_tut_envelope

The system is almost identical to the system in the previous section, except:

The model contains only one SimRF Outport block and only one scope. The SimRF environment outputs in-phase and quadrature modulations of the 1-GHz signal. In the SimRF Outport block, the

**Output**parameter is set to`In-phase and quadrature baseband`. Since the system is not configured to output a real passband signal, the carrier is not simulated.In the Configuration Parameters dialog box, the

**Fixed-step size (fundamental sample time)**parameter is greater. Its value is`5e-9`instead of`1/16*1e-9`.

Running the model produces the following output at the scope.

The I/Q Scope displays the in-phase and quadrature baseband components of the 1-GHz signal. The 1-GHz carrier itself does not appear in the output. The results correspond to the real and imaginary parts of the Complex modulation at the input of the system.

In contrast to the models in the previous two sections, Simulink works differently in this model. Because the modulating signals are constant in this example, only two sample points are needed. To simulate a time-varying modulating signal, Simulink can use a fixed time step on the order of the reciprocal of its bandwidth.

The model uses a value of `5e-9` for the **Fixed-step
size (fundamental sample time)** parameter. This value equals
the **Stop time** because, in this case, the modulating
signals are constant. Compared to the preceding examples, which use
a sample time of `1/16*1e-9`, this model simulates
accurately with a time step 80 times larger. This step size results
in a reduction of total sample time by a factor of 80, excluding the
initial time step at time 0.

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