Modeling Noise :: Modeling an RF System (RF Blockset™)

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Modeling Noise

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Amplifier and Mixer Noise Specifications Adding Noise to Your System Plotting Noise

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Amplifier and Mixer Noise Specifications

You only need to specify noise information for the physical amplifier and mixer blocks that generate noise other than resistor noise. For the other blocks, the blockset calculates the noise automatically based on the resistor values.

You define noise for the physical amplifier and mixer blocks through one of the following specifications:

Spot noise data in the data source.
Spot noise data in the block dialog box.
Spot noise data (rfdata.noise class) object in the block dialog box.
Frequency-independent noise figure, noise factor, or noise temperature value in the block dialog box.
Frequency-dependent noise figure data (rfdata.nf) object in the block dialog box.

The following table summarizes the noise specification options for each type of physical amplifier and mixer block.

Block	Noise Specification
General Amplifier	Spot noise data (using a Touchstone, P2D, S2D, or AMP data file) OR Spot noise data, noise figure value, noise factor value, noise temperature value, `rfdata.noise`, or `rfdata.nf` object in the block dialog box
S-Parameters Amplifier Y-Parameters Amplifier Z-Parameters Amplifier	Spot noise data, noise figure value, noise factor value, noise temperature value, `rfdata.noise`, or `rfdata.nf` object in the block dialog box
General Mixer	Spot noise data (using a Touchstone, P2D, S2D, or AMP data file) OR Spot noise data, noise figure value, noise factor value, noise temperature value, `rfdata.noise`, or `rfdata.nf` object in the block dialog box
S-Parameters Mixer Y-Parameters Mixer Z-Parameters Mixer	Spot noise data, noise figure value, noise factor value, noise temperature value, `rfdata.noise`, or `rfdata.nf` object in the block dialog box

Adding Noise to Your System

To simulate the noise of a physical subsystem, you perform the following tasks:

Specifying or Importing Noise Data

The method you use to add noise data to a block depends on whether you are specifying noise data manually or importing spot-noise data.

The following table provides instructions for adding noise data.

Noise Specification	Instructions
Frequency-independent noise figure	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Noise figure`, and enter the noise figure value in the Noise figure (dB) parameter.
Frequency-dependent noise figure	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Noise figure`, and enter the name of the `rfdata.nf` object in the Noise figure (dB) parameter.
Noise factor	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Noise factor`, and enter the noise factor value in the Noise factor parameter.
Noise temperature	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Noise temperature`, and enter the noise temperature value in the Noise temperature (K) parameter.
Spot noise data (in a block dialog box)	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Spot noise data`. Enter the spot noise information in the Minimum noise figure (dB), Optimal reflection coefficient, and Equivalent normalized noise resistance parameters.
Spot noise data (from a data object)	In the Noise Data tab of the block dialog box, set the Noise type parameter to `Noise figure` and enter the name of the `rfdata.noise` object in the Noise figure (dB) parameter.
Spot noise data (from a file)	Import file data that includes noise information into the Data file or RFCKT object parameter of the General Amplifier or General Mixer block.

Note If you import file data with no noise information into a General Amplifier or General Mixer block, the Noise Data tab lets you add noise data manually in the block dialog box.

Adding Noise to the Simulation

To include noise in the simulation, you must select the Add noise check box on the Input Port block dialog box. This check box is selected by default.

For information on how the blockset simulates noise, see Modeling Noise in an RF System.

Plotting Noise

RF Blockset software models communications systems. The noise in these systems has a very small amplitude, typically from 1e-6 to 1e-12 Watts. In contrast, the default signal power of a Communications Blockset modulator block is 1 Watt at a nominal 1 ohm. Therefore, the signal-to-noise ratio in an RF system simulation is large, making it difficult to view the noise RF Blockset blocks add to your signal.

To display the noise on a plot, you might need to attenuate the signal amplitude to a value within a couple orders of magnitude of the noise.

For example, suppose you have the following model that contains a multitone test signal source.

When you simulate this model, Simulink brings up several windows showing the input and output for the physical subsystem. The Input - Frequency Domain window shown in the following figure displays the input signal in the frequency domain.

Input Signal Spectrum

The Real Part of Input - Time Domain window displays the real part of the complex-valued input signal in the time domain.

Real Part of Input Signal

In the model, the physical subsystem adds noise to the input signal. The Output - Frequency Domain window shows the noisy output signal in the frequency domain.

Output Signal Spectrum

The amplitude of the signal is large compared to the amplitude of the noise, so the noise is not visible in the Real Part of Output - Time Domain window that shows the real part of the time-domain output signal. Therefore, you must attenuate the amplitude of the input signal to display the noise of the time-domain output signal.

Real Part of Output Signal

Attenuate the amplitude of the input signal by setting the Gain parameter to 1e-3. This is equivalent to attenuating the input signal by 60 dB. When you run the model again, the two signal peaks are not as pronounced in the Output - Frequency Domain window.

Output Signal Spectrum for Attenuated Input