Outport

Convert RF Blockset signal to Simulink output signals

Library:
RF Blockset / Circuit Envelope / Utilities

Description

The Outport block outputs carrier modulation signals in the RF Blockset™ circuit envelope simulation environment as Simulink^® signal. For an introduction to RF simulation, see the example, Simulate High Frequency Components.

The output port senses current and voltage complex envelope or real passband signals. Complex baseband signals consist of in-phase (I_k) and quadrature (Q_k) components centered around each specified center frequency f_k.

The Sensor type parameter determines which signal the block measures, and the Output parameter defines the format of the Simulink signal.

Note

Outport block Real passband output does not support frame-based processing (supported by the Configuration blocks). This block errors if the Samples per frame is more than 1 in the configuration block.

Parameters

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`Sensor type` — Type of signal measured by sensor
`Ideal voltage` (default) | `Ideal current` | `Power`

Type of signal measured by sensor, specified as:

Ideal voltage — The block outputs the modulations of the voltage signal at the specified Carrier frequencies in the format specified by the Output parameter. This is the recommended option to sense a signal without adding a loading impedance and changing matching conditions.
Ideal current — The block outputs the modulations of the current signal at the specified Carrier frequencies in the format specified by the Output parameter.
Power — The block outputs the modulations of the voltage signal at the specified Carrier frequencies and scaled with respect to the specified load impedance. This is the recommended option to sense a signal generated in RF Blockset 50 Ohm environment or a different reference impedance. When you use the power option , the output port automatically inserts a load impedance in your circuit.

$\frac{\sqrt{Re (Z_{l})}}{Z_{l}} v (t)$
where Z_l is the value of the Load impedance (ohms) parameter.

`Load impedance (Ohm)` — Load impedance of RF circuit
`inf` (default) | vector of positive integers in ohms

Load impedance of RF circuit used to measure signal power, specified as a vector of positive integers in ohms. When you use the power option , the output port automatically inserts a load impedance in your circuit. When you use multiple Outport blocks as power sources at the same node in a given circuit, the resulting load is the parallel combination of the specified load impedances.

Dependencies

To enable this parameter, select Power in Sensor type.

`Output` — Format of output signals
`Complex Baseband` (default) | `In-phase and Quadrature Baseband` | `Magnitude and Angle Baseband` | `Real Passband`

Format of output signals, specified as one of the following:

Complex Baseband — The block outputs a vector of complex-valued signals I_k(t) + j · Q_k(t) at the port labeled SL. The kth element of the vector is the kth frequency specified by the Carrier frequencies parameter.
In-phase and Quadrature Baseband — The block outputs two vectors of real-valued signals I_k(t) and Q_k(t) at the I port and Q port, respectively. The signal at the I port contains the in-phase components, and the signal at the Q port contains the quadrature components. The kth element of the vector is the kth frequency specified by the Carrier frequencies parameter. The quadrature component of a signal with carrier frequency equal to 0 Hz is zero.
Magnitude and Angle Baseband — The block outputs two real-valued vectors, whose elements are the magnitude and phase angle of the modulation. The Mag port outputs |I_k(t) + j · Q_k(t)| and the Ang port outputs Arg[I_k(t) + j · Q_k(t)]. The kth element of the vector is the kth frequency specified by the Carrier frequencies parameter.
Real Passband — The block outputs real passband signals by combining envelope and carrier signals for all frequencies listed under Carrier frequencies. When using the Real Passband option, the solver takes time steps small enough to resolve the carrier. Thus, simulation speed improvements from envelope simulation may be limited.
$o u t = Re a l (\sum_{k = 1}^{N} (I_{k} (t) + j \cdot Q_{k} (t)) \cdot e^{j 2 π f_{k} t})$
where t is the value of Load impedance (ohms) parameter.

`Automatically compute output step size` — Determine optimal time step to resolve highest listed carrier frequency
`on` (default) | `off`

Determine optimal time step to resolve highest listed carrier frequency, specified as a on or off. Select this parameter to allow RF Blockset to determine the optimal time step to resolve the highest listed carrier frequency. Clear the parameter selection to enter a value for step size.

`Step size` — Time step
`1e-6 s` (default) | positive integer in seconds

Time step, specified as a positive integer in seconds. The step size should be small enough to resolve the fastest carrier signal. The size helps to avoid passband output undersampling and aliasing effects.

Set the time step value to -1 to inherit the time step specified from Step size in Configuration block.

`Carrier frequencies` — Carrier frequencies
`0 Hz` (default) | vector of positive integers in Hz

Carrier frequencies, specified as a vector of positive integers in Hz. In carrier frequencies, the elements are a combination of fundamental tones and corresponding harmonics in the Configuration block.

`Ground and hide negative terminals` — Ground RF circuit terminals
`on` (default) | `off`

Ground RF circuit terminals, specified as a on or off. Select this parameter to ground and hide the negative terminals. Clear the parameter to expose the negative terminals. By exposing these terminals, you can connect them to other parts of your model.

By default, this option is selected.

Model Examples

Passband Signal Representation in Circuit Envelope

The relationship between two signal representations in RF Blockset™ Circuit Envelope: complex baseband (envelope) signal and passband (time domain) signal. The step size of a RF Blockset solver is usually much larger than the period of the carrier, so upsampling is necessary to construct a reasonable passband signal.

Validating IP2/IP3 Using Complex Signals

Use the RF Blockset™ Circuit Envelope library to run a two-tone experiment that measures the second- and third-order intercept points of an amplifier. The model computes the intercept points of the amplifier from the modulated signal power measured on each carrier, verifying the behavior of the RF Blockset system. These values are confirmed using the RF Budget Analyzer app and a measurement testbench.

More About

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Multi-Carrier Envelope Simulation

Using the Inport block you can specify the complex envelopes of your input signals and import them as RF signals for multi-carrier simulation.

The Configuration block automatically determines the fundamental tones specified in the input ports and proposes a suitable harmonic order to capture the non-linearity of the system. You can also manually specify the harmonic order for each fundamental tone in the simulation.

In the input port, you can specify as many carrier frequencies as you want. It is recommended that you trade off the simulation bandwidth (inversely proportional to the simulation time step) and the total number of simulation frequencies.

Real Passband Formula

Normalized carrier power option in the Configuration block defines the passband formula:

When this option is selected, RF Blockset interprets complex envelope I+jQ signal for the k^th carrier as,

$s_{k} (t) = I (t) \sqrt{2} \cos (2 π f_{k} t) - Q (t) \sqrt{2} \sin (2 π f_{k} t)$
When this option is not selected, the signal on the k^th

$s_{k} (t) = I (t) \cos (2 π f_{k} t) - Q (t) \sin (2 π f_{k} t)$
In both cases, the signal for zero-frequency (DC) carrier is x( t ) = I( t ). The final output signal is computed as s(t) = sum( s_k )

Formula for Time Step

The formula for the time step selected is:

$\min (h, ((1 / 2 π f) \div 8))$

f is the largest listed carrier frequency.
h is the time step listed in Configuration block.

Algorithms

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How to Use Outport Block

Sensing Signals at Different Nodes of RF Chain

Consider an RF chain composed by several stages. You want to sense and inspect the signal behavior at different intermediate nodes.

Use the power input port and power sensor port at the input and output of your chain, as gateways between Simulink (reference 1Ohm) and the RF domain.

Use the voltage or current output ports connected to the intermediate nodes and branches that you want to inspect. To measure the power of a voltage signal, change the default spectrum analyzer reference impedance to 50Ohm.

Sense Complex Equivalent Baseband Signal for Digital Signal Processing

Output signal is a combination of (digital communication) complex equivalent baseband signals (I,Q). For each envelope, assume an implicit center frequency for the signal that is equal to the carrier frequency,F_c.

Enter the array F_c in the Carrier Frequencies parameter corresponding to the center frequency of the envelopes that you want to sense. The output signals is an array of complex (I,Q) envelopes.
The output port of sensor type power provides a termination (by default 50Ohm) at the end of the chain.
The simulation step size in the Configuration block is the same as the sample time of the Simulink signal, and it is not related to the carrier frequency.

Sense Real Passband Signal

Output signal is a (digital communication) complex baseband signal (I,Q) resulted from a direct conversion receiver. Assume that no carrier is associated with the output signal.

Use two Outport blocks for the I and Q components of the signal. Set the Carrier Frequencies parameter of each Outport block to 0. Use the real passband option to sense a real signal rather than a complex signal with quadrature component equal to 0.
The output ports of sensor type power provide a termination (by default 50Ohm) at the end of the chain.
To down-convert the signal, use an IQ Demodulator block. Set the Local oscillator frequency to F_c equal to the center frequency of the input signal (direct conversion).
The simulation step size in the configuration block is the same as the sample time of the Simulink signal, and it is not related to the Local Oscillator frequency.

Down Convert Signal to IF and Sense Complex Equivalent Baseband Signal

Output signal is a (digital communication) complex equivalent baseband signal (I,Q) down-converted to intermediate frequency (IF). Apply digital signal processing techniques for processing the complex equivalent baseband information of the signal.

Set the Carrier frequencies parameter of the Outport block to IF. Use the complex baseband option.
Use the Mixer block for down-conversion. Set the LO carrier frequency to LO = RF-IF. The output port will behave as an ideal filter and select only the down-converted signal. The envelope at RF+LO = 2RF-IF frequency is simulated but it is not sensed by the output port.
The simulation step size in the configuration block is the same as the sample time of the Simulink input signal, and it is not related to the IF, RF or LO frequencies.

Down Convert Signal to IF and Sense Real Passband Signal

Output signal is a (digital communication) signal (I,Q) down-converted to intermediate frequency (IF). Apply analog signal processing techniques to the output signal.

Set the Carrier frequencies parameter of the Output block to IF. Use the real passband option.
If the intermediate frequency is within the simulation bandwidth defined in the configuration block, Use the same step size in the output without the need for resampling the signal.
If the intermediate frequency is not within the simulation bandwidth defined in the configuration block, you need to resample the signal (as described in the real-passband formula) to correctly resample the carrier.
Use the Mixer block. Set the LO carrier frequency to LO = RF-IF. The output port will behave as an ideal filter, and select only the down-converted signal. The envelope at RF+LO = 2RF-IF frequency is simulated but it is not sensed by the output port.
The simulation step size in the configuration block is the same as the sample time of the Simulink input signal. All the blocks in the RF Blockset network connected to the configuration block are executed with the same step size. The time step of the outport, when the real passband option is selected, might differ from the time step of the input Simulink signal and of the time step set in the configuration block.

Documentation

Outport

Description

Parameters

`Sensor type` — Type of signal measured by sensor
`Ideal voltage` (default) | `Ideal current` | `Power`