## Convert to and from Simulink Signals

### Signal Conversion Specifications

When you simulate an RF model, the blockset must convert the
mathematical Simulink^{®} signals to and from the physical modeling
environment. The following figure shows the signals involved in the
conversion.

Where:

*Z*is the_{S}**Source impedance (ohms)**parameter of the Input Port block.*Z*is the_{L}**Load impedance (ohms)**parameter of the Output Port block.

There are two options for interpreting the Simulink signal that enters the Input Port block:

*S*_{in}is the incident power wave. For more information about this option, see Interpret Simulink Signals as Incident Power Waves.*S*_{in}is the source voltage. For more information about this option, see Interpret Simulink Signals as Source Voltages.

### Interpret Simulink Signals as Incident Power Waves

The blockset provides the option to interpret the input Simulink signal, *S*_{in},
as the incident power wave, *a _{p1}*,
at the first port of the RF system. The following figure shows the
model for this interpretation.

In the figure, *b _{p2}* is
the transmitted power wave at the second port of the RF system. This
is the signal at the output of the Output Port block,

*S*

_{out}.

For a 2-port RF system, the incident and transmitted power waves are defined as:

$$\begin{array}{l}{a}_{p1}=\frac{{V}_{S}}{2\sqrt{{R}_{S}}}\\ {b}_{p2}=\frac{\sqrt{{R}_{L}}}{{Z}_{L}}{V}_{L}\end{array}$$

where:

*Z*, the_{S}**Source impedance (ohms)**parameter of the Input Port block, is defined as:*Z*=_{S}*R*+_{S}*j**X*_{S}*Z*, the_{L}**Load impedance (ohms)**parameter of the Output Port block, is defined as:*Z*=_{L}*R*+_{L}*j**X*_{L}

Solving the power wave equations for *S*_{in} and *S*_{out} gives
the following relationships:

$$\begin{array}{l}{S}_{in}=\frac{{V}_{S}}{2\sqrt{{R}_{S}}}\\ {S}_{out}=\frac{\sqrt{{R}_{L}}}{{Z}_{L}}{V}_{L}\end{array}$$

The implications of this interpretation are:

$${\left|{S}_{in}\right|}^{2}$$ is equal to the power available from the source,

*P*._{avs}$${\left|{S}_{out}\right|}^{2}$$ is equal to the power delivered to the load,

*P*._{out}

For a linear RF system, $${P}_{out}={G}_{t}{P}_{avs}$$ where *G _{t}* is
the transducer power gain. As a result, the Simulink signals
at the input and output of the RF system have the following relationship:

$${\left|{S}_{out}\right|}^{2}={G}_{t}{\left|{S}_{in}\right|}^{2}$$

**Note**

You can plot *G _{t}* from
the Output Port block's

**Visualization**tab.

### Interpret Simulink Signals as Source Voltages

The blockset provides the option to interpret the input Simulink signal, *S*_{in},
as the source voltage, *V _{S}*,
of the RF system. The following figure shows the model for this interpretation.

With this interpretation,
the signal at the output of the Output Port block is the load voltage, *V _{L}*.

The blockset interpretation of the input Simulink signal
as the source voltage, *V*_{S},
produces different results than the interpretation where the input Simulink signal
is the incident power wave. When the source and load impedances are
the same and real, the former interpretation produces 6 dB of loss
compared to the latter.

### Specify Input Signal Conversions

To specify the way in which the blockset interprets the input Simulink signal,
you change the value of the **Treat input Simulink signal
as** parameter in the Input Port dialog box. The available
parameter values are:

`Incident power wave`

— Interpret the input signal as the incident power wave.`Source voltage`

— Interpret the input signal as the source voltage.

## See Also

General Amplifier | Input Port | Output Port | S-Parameters Amplifier