Output Port

Connection block from RF physical blocks to Simulink environment

Library

Input/Output Ports sublibrary of the Physical library

Description

The Output Port block produces the baseband-equivalent time-domain response of an input signal traveling through a series of RF physical components. The Output Port block

1. Partitions the RF physical components into linear and nonlinear subsystems.

2. Extracts the complex impulse response of the linear subsystem for baseband-equivalent modeling of the RF linear system.

3. Extracts the nonlinear AMAM/AMPM modeling for RF nonlinearity.

The Output Port block also serves as a connecting port from an RF physical part of the model to the Simulink^®, or mathematical, part of the model. For more information about how the Output Port block converts the physical modeling environment signals to mathematical Simulink signals, see Convert to and from Simulink Signals.

Note

Some RF blocks require the sample time to perform baseband modeling calculations. To ensure the accuracy of these calculations, the Input Port block, as well as the mathematical RF blocks, compare the input sample time to the sample time you provide in the mask. If they do not match, or if the input sample time is missing because the blocks are not connected, an error message appears.

Linear Subsystem

For the linear subsystem, the Output Port block uses the Input Port block parameters and the interpolated S-parameters calculated by each of the cascaded physical blocks to calculate the baseband-equivalent impulse response. Specifically, it

1. Determines the modeling frequencies f as an N-element vector. The modeling frequencies are a function of the center frequency f_c, the sample time t_s, and the finite impulse response filter length N, all of which you specify in the Input Port block dialog box.

   The nth element of f, f_n, is given by

   $$\begin{array}{cc}{f}_n=f_{\min }+\frac{n-1}{t_{s}N}& n=1,\mathrm{...},N\end{array}$$

   where

   $$f_{\min }=f_c-\frac{1}{2t_s}$$

2. Calculates the passband transfer function for the frequency range as

   $$H(f)=\frac{V_L(f)}{V_S(f)}$$

   where V_S and V_L are the source and load voltages, and f represents the modeling frequencies. More specifically,

   $$H(f)=\frac{S_{21}\left(1+{\Gamma }_l\right)\left(1-{\Gamma }_s\right)}{2\left(1-S_{22}{\Gamma }_l\right)\left(1-{\Gamma }_{in}{\Gamma }_s\right)}$$

   where

   $$\begin{array}{l}{\Gamma }_l=\frac{Z_l-Z_o}{Z_l+Z_o}\\ {\Gamma }_s=\frac{Z_s-Z_o}{Z_s+Z_o}\\ {\Gamma }_{in}=S_{11}+\left(S_{12}{S}_{21}\frac{{\Gamma }_l}{\left(1-S_{22}{\Gamma }_l\right)}\right)\end{array}$$

   and

   • Z_S is the source impedance.

   • Z_L is the load impedance.

   • S_ij are the S-parameters of a two-port network.

   The blockset derives the passband transfer function from the Input Port block parameters as shown in the following figure:

   

3. Translates the passband transfer function to baseband as H(f – f_c), where f_c is the specified center frequency.

   The baseband transfer function is shown in the following figure.

   

4. Obtains the baseband-equivalent impulse response by calculating the inverse FFT of the baseband transfer function. For faster simulation, the block calculates the IFFT using the next power of 2 greater than the specified finite impulse response filter length. Then, it truncates the impulse response to a length equal to the filter length specified.

For the linear subsystem, the Output Port block uses the calculated impulse response as input to the DSP System Toolbox™ Digital Filter Design block to determine the output.

Nonlinear Subsystem

The nonlinear subsystem is implemented by AM/AM and AM/PM nonlinear models, as shown in the following figure.

The nonlinearities of AM/AM and AM/PM conversions are extracted from the power data of an amplifier or mixer by the equations

$$\begin{array}{c}A{M}_{out}=\sqrt{R_l{P}_{out}}\\ P{M}_{out}=\phi \\ A{M}_{in}=\sqrt{R_s{P}_{in}}\end{array}$$

where AM_in is the AM of the input voltage, AM_out and PM_out are the AM and PM of the output voltage, R_s is the source resistance (50 ohms), R_l is the load resistance (50 ohms), P_in is the input power, P_out is the output power, andϕ is the phase shift between the input and output voltage.

Note

You can provide power data via a .amp file. See AMP File Data Sections (RF Toolbox) for information about this format.

The following figure shows the original power data of an amplifier.

This figure shows the extracted AM/AM nonlinear conversion.

Parameters

Main Tab

Load impedance (ohms)

Load impedance of the RF network described in the physical model to which it connects.

Visualization Tab

This tab shows parameters for creating plots if you display the Output Port mask after you perform one or more of the following actions:

• Run a model with two or more blocks between the Input Port block and the Output Port block.

• Click the Update Diagram button to initialize a model with two or more blocks between the Input Port block and the Output Port block.

For information about plotting, see Create Plots.