MATLAB: Does the rfdata.nf constructor’s Data property unit (related to noise figure) specify Watts in the RF Toolbox 2.1 (R2007a) documentation

RF Toolbox

The documentation for RF Toolbox specifies the following under Properties –>Data –>Description:

 "M-element vector of  *** noise figure data, in watts ***, that corresponds to the frequencies stored in the Freq property. The default is 0..."

RF engineers typically refer to "noise figure" and "noise factor". They are related by

 Noise figure = 10 log10(Noise factor)

Noise factor is a UNITLESS quantity. "Noise figure" data is conventionally expressed in dB (NOT dBm, or dBW, etc).

I would like clarification of the units being used.

Best Answer

This bug has been fixed in RF Toolbox 2.3 (R2008a). For previous product releases, read below for any possible workarounds:

The documentation should read as follows:

 M-element vector of noise figure data, in dB, that corresponds to the frequencies stored in the Freq property. The default is 0.

The implementation and M-help of RFDATA.NF are correct. To see the M-help, type the following at the command line.

help rfdata.nf

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MATLAB: Can I specify a frequency-dependent IP3 parameter in the RF Blockset

This enhancement has been incorporated in Release 2008b (R2008b). For previous product releases, read below for any possible workarounds:

To work around this issue, use the General Circuit Element block from the Black Box Elements library. Use the following command line functionality to define an RFCKT object called mixer that specifies the mixer behavior and then set the 'RFCKT object' parameter of the General Circuit Element block to the MATLAB variable mixer:

% mixer for the mask parameter ‘RFCKT object’ of the General Circuit Element block % is an RFCKT.MIXER object and should be created in MATLAB workspace:
mixer = rfckt.mixer;
% Create data objects for frequency-dependent S-parameters, spot noise and IP3: 
freq = [1e9 1.4e9];     % two frequencies


sparams(:,:,1) = [-0.7247 - 0.4813i        0;           -0.6857 + 1.7827i  -0.0741 - 0.3216i];
sparams(:,:,2) = [-0.7318 - 0.4715i   0.0014 + 0.0005i; -0.6560 + 1.7980i  -0.0761 - 0.3190i];
sparamsData = rfdata.network('Type', 'S', 'Freq', freq, 'Data', sparams);
freq = [1e9 1.4e9];                       % two frequencies
fmin = [12.08 13.40];                     % Minimum noise figure in dB
gopt = [0.2484-1.2102j 1.0999-0.9295j];   
% "gopt" is a source reflection coefficient to realize minimum noise figure
rn = [0.26 0.45];                         % Equivalent normalized noise resistance
noiseData = rfdata.noise('Freq', freq, 'FMIN', fmin, 'GAMMAOPT', gopt, 'RN', rn);
freq = [1e9 1.4e9];     % two frequencies
ip3 = [0.001 0.05];     % IP3 in Watts at two frequencies
ip3Data = rfdata.ip3('Type', 'IIP3', 'Freq', freq, 'Data', ip3);
% Set mixer’s three properties: NetworkData, NoiseData and NonlinearData with
% three data objects:
mixer.NetworkData = sparamsData
mixer.NoiseData = noiseData
mixer.NonlinearData = ip3Data

MATLAB: How to interpret the parameters of the “Phase Noise” block under “RF Impairments” in the Communications Blockset

The "Phase Noise" block adds phase noise to the input signal such that the power density spectrum of the output signal satisfies the following criteria (specified via the block dialog parameters):

 The power density spectrum of the output signal, after magnitude scaling such that the carrier power is 0 dB, equals X dB/Hz at a frequency offset of F Hz from the carrier frequency.

X is the "Phase Noise Level (dBc/Hz)" parameter and F is the "Frequency offset (Hz)" parameter of the "Phase Noise" block. The attached model and MATLAB file illustrate the interpretation of the block parameters. Save the attached model dBc_per_Hz_test6.mdl and the function plot_dbc_per_hz.m files in a suitable directory and open the model, by typing the following command in the MATLAB command window:

dBc_per_Hz_test6

Note that this model is compatible with Communication Blockset 3.2 (R14SP3).

1. The model has a "Constant" signal feeding into a "Phase Noise" block. This simulates phase noise being added to a carrier signal (0 Hz carrier frequency). The block parameters are set at the following values:

Phase Noise Level (dBc/Hz) = -100

Frequency offset (Hz) = 1MHz

2. The Signal from the "Phase Noise" block is then passed through a "Power Spectrum Estimate". This block returns the power spectrum of the input signal, the total power in the signal and also the scaled dBc/Hz of the signal. The "Scaled dBc/Hz" output is the power spectrum density of the input signal that has been scaled such that the carrier power is 0 dB. This is the reason it is called dBc (dB carrier). Look under the mask of the "Power Spectrum Estimate" block to see how the power spectrum is calculated (right click on the block and select "Look under mask").

3. The model is set up such that at the end of the simulation, the "plot_dbc_per_hz.m" function is called. This function plots the dBc/Hz of the "Phase Noise" block output signal. If you run the simulation, you will observe that when the simulation ends, this plot appears and you will see that the dBc/Hz will be -100 at 1MHz (from carrier frequency) (as specified in the "Phase Noise" Block).

Thus the noise added to the carrier signal is at a level of -100 dBc/Hz at a frequency offset of 1MHz from the carrier frequency.

The entire model is adequately commented for you to be able to understand the methodology to obtain the dBc/Hz of a signal. Right click on the "Power Spectrum Estimate" and select "Look under mask". You will observe the following

1. A Hann window is used to scale the input signal samples.

2. The FFT^2 of the windowed signal is computed

3. Spectral averaging is performed to obtain a time averaged power spectrum

4. The power spectrum is scaled to obtain the power spectrum in dBc. Note that the scaling assumes that the largest signal (signal frequency with largest FFT^2) is assumed to be the carrier. Double-click on the "dBc scaling" block to see the implementation of the scaling.

5. The power spectrum in dBc is frequency scaled to obtain the power spectrum density in dBc/Hz.

Best Answer

Related Solutions

MATLAB: Can I specify a frequency-dependent IP3 parameter in the RF Blockset

MATLAB: How to interpret the parameters of the “Phase Noise” block under “RF Impairments” in the Communications Blockset

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