General Amplifier

Model nonlinear amplifier described by rfdata object or file data

Library

Amplifiers sublibrary of the Physical library

Description

The General Amplifier block models the nonlinear amplifier described by a data source. The data source consists of either an RF Toolbox™ data (rfdata.data) object or data from a file.

Network Parameters

If network parameter data and corresponding frequencies exist as S-parameters in the data source, the General Amplifier block interpolates the S-parameters to determine their values at the modeling frequencies. If the network parameters are Y- or Z-parameters, the block first converts them to S-parameters. For more information, see SimRF Equivalent Baseband Algorithms.

Nonlinearity

If power data exists in the data source, the block extracts the AMAM/AMPM nonlinearities from the power data.

If the data source contains no power data, then you can introduce nonlinearities into your model by specifying parameters in the Nonlinearity Data tab of the General Amplifier block dialog box. Depending on which of these parameters you specify, the block computes up to four of the coefficients c1, c3, c5, and c7 of the polynomial

FAM/AM(s)=c1s+c3|s|2s+c5|s|4s+c7|s|6s

that determines the AM/AM conversion for the input signal s. The block automatically calculates c1, the linear gain term. If you do not specify additional nonlinearity data, the block operates as a linear amplifier. If you do, the block calculates one or more of the remaining coefficients as the solution to a system of linear equations, determined by the following method.

  1. The block checks whether you have specified a value other than Inf for:

    • The third-order intercept point (OIP3 or IIP3).

    • The output power at the 1-dB compression point (P1dB,out).

    • The output power at saturation (Psat,out).

    In addition, if you have specified Psat,out, the block uses the value for the gain compression at saturation (GCsat). Otherwise, GCsat is not used. You define each of these parameters in the block dialog box, on the Nonlinearity Data tab.

  2. The block calculates a corresponding input or output value for the parameters that you have specified. In units of dB and dBm,

    Psat,out+GCsat=Psat,in+GlinP1dB,out+1=P1dB,in+GlinOIP3=IIP3+Glin

    where Glin is c1 in units of dB.

  3. The block formulates the coefficients c3, c5, and c7, where applicable, as the solutions to a system of one, two, or three linear equations. The number of equations is equal to the number of parameters that you provide. For example, if you specify all three parameters, the block formulates the coefficients according to the following equations:

    Psat,out=c1Psat,in+c3(Psat,in)3+c5(Psat,in)5+c7(Psat,in)7P1dB,out=c1P1dB,in+c3(P1dB,in)3+c5(P1dB,in)5+c7(P1dB,in)70=c1IIP3+c3

    The first two equations are the evaluation of the polynomial FAM/AM(s) at the points (Psat,in,Psat,out) and (P1dB,in,P1dB,out), expressed in linear units (such as W or mW) and normalized to a 1-Ω impedance. The third equation is the definition of the third-order intercept point.

    The calculation omits higher-order terms according to the available degrees of freedom of the system. If you specify only two of the three parameters, the block does not use the equation involving the parameter you did not specify, and eliminates any c7 terms from the remaining equations. Similarly, if you provide only one of the parameters, the block uses only the solution to the equation involving that parameter and omits any c5 or c7 terms.

If you provide vectors of nonlinearity and frequency data, the block calculates the polynomial coefficients using values for the parameters interpolated at the center frequency.

Active Noise

You can specify active block noise in one of the following ways:

  • Spot noise data in the data source.

  • Spot noise data in the block dialog box.

  • Spot noise data (rfdata.noise) object in the block dialog box.

  • 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 latter four options are only available if noise data does not exist in the data source.

If you specify block noise as spot noise data, the block uses the data to calculate noise figure. The block first interpolates the noise data for the modeling frequencies, using the specified Interpolation method. It then calculates the noise figure using the resulting values.

Operating Conditions

Agilent® P2D and S2D files define block parameters for several operating conditions. Operating conditions are the independent parameter settings that are used when creating the file data. By default, SimRF™ Equivalent Baseband software defines the block behavior using the parameter values that correspond to the operating conditions that appear first in the file. To use other property values, you must select a different operating condition in the General Amplifier block dialog box.

Data Consistency

If the data source is a MathWorks™ AMP file or an Agilent S2D file that contains both network parameter data and power data, the blockset checks the data for consistency and reconciles it as necessary.

The blockset compares the small-signal amplifier gain defined by the network parameters, S21, and by the power data, Pout-Pin. The discrepancy between the two is computed in dBm using the following equation:

ΔP=S21(fP)Pout(fP)+Pin(fP)(dBm)

where fP is the lowest frequency for which power data is specified.

If ΔP is more than 0.4 dB, a warning appears, and the blockset adds ΔP to the output power values at each specified input power value to resolve the discrepancy for simulation. The following graph shows this discrepancy.

Dialog Box

Main Tab

Data source

Determines the source of the data that describes the amplifier behavior. The data source must contain network parameters and may also include noise data, nonlinearity data, or both. The value can be Data file or RFDATA object.

Data file

If Data source is set to Data file, use this field to specify the name of the file that contains the amplifier data. The file name must include the extension. If the file is not in your MATLAB® path, specify the full path to the file or click the Browse button to find the file.

RFDATA object

If Data source is set to RFDATA object, use this field to specify an RF Toolbox data (rfdata.data) object that describes an amplifier. You can specify the object as:

  • The handle of a data object previously created using RF Toolbox software.

  • An RF Toolbox command such as rfdata.data('Freq',1e9,'S_Parameters',[0 0; 0.5 0]), which creates a data object.

  • A MATLAB expression that generates such an object.

Interpolation method

The method used to interpolate the network parameters. The following table lists the available methods describes each one.

MethodDescription
Linear (default)Linear interpolation
SplineCubic spline interpolation
CubicPiecewise cubic Hermite interpolation

Noise Data Tab

Noise type

Type of noise data. The value can be Noise figure, Spot noise data, Noise factor, or Noise temperature. This parameter is disabled if the data source contains noise data.

Noise figure (dB)

Scalar ratio or vector of ratios, in decibels, of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (Si/Ni)/(So/No). This parameter is enabled if Noise type is set to Noise figure.

Minimum noise figure (dB)

Minimum scalar ratio or vector of minimum ratios of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (Si/Ni)/(So/No). This parameter is enabled if Noise type is set to Spot noise data.

Optimal reflection coefficient

Optimal amplifier source impedance. This parameter is enabled if Noise type is set to Spot noise data. The value can be a scalar or vector.

Equivalent normalized resistance

Resistance or vector of resistances normalized to the resistance value or values used to take the noise measurement. This parameter is enabled if Noise type is set to Spot noise data.

Noise factor

Scalar ratio or vector of ratios of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (Si/Ni)/(So/No). This parameter is enabled if Noise type is set to Noise factor.

Noise temperature (K)

Equivalent temperature or vector of temperatures that produce the same amount of noise power as the amplifier. This parameter is enabled if Noise type is set to Noise temperature.

Frequency (Hz)

Scalar value or vector corresponding to the domain of frequencies over which you are specifying the noise data. If you provide a scalar value for your noise data, the block ignores the Frequency (Hz) parameter and uses the noise data for all frequencies. If you provide a vector of values for your noise data, it must be the same size as the vector of frequencies. The block uses the Interpolation method specified in the Main tab to interpolate noise data.

Nonlinearity Data Tab

IP3 type

Type of third-order intercept point. The value can be IIP3 (input intercept point) or OIP3 (output intercept point). This parameter is disabled if the data source contains power data or IP3 data.

IP3 (dBm)

Value of third-order intercept point. This parameter is disabled if the data source contains power data or IP3 data. Use the default value, Inf, if you do not know the IP3 value. This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).

1 dB gain compression power (dBm)

Output power value (P1dB,out) at which gain has decreased by 1 dB. This parameter is disabled if the data source contains power data or 1-dB compression point data. Use the default value, Inf, if you do not know the 1-dB compression point. This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).

Output saturation power (dBm)

Output power value (Psat,out) that the amplifier produces when fully saturated. This parameter is disabled if the data source contains output saturation power data. Use the default value, Inf, if you do not know the saturation power. If you specify this parameter, you must also specify the Gain compression at saturation (dB). This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).

Gain compression at saturation (dB)

Decrease in gain (GCsat) when the power is fully saturated. The block ignores this parameter if you do not specify the Output saturation power (dBm). This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).

Frequency (Hz)

Scalar or vector value of frequency points corresponding to the third-order intercept and power data. This parameter is disabled if the data source contains power data or IP3 data. If you use a scalar value, the IP3 (dBm), 1 dB gain compression power (dBm), and Output saturation power (dBm) parameters must all be scalars. If you use a vector value, one or more of the IP3 (dBm), 1 dB gain compression power (dBm), and Output saturation power (dBm) parameters must also be a vector.

Visualization Tab

For information about plotting, see Create Plots. Use rftool or the RF Toolbox plotting functions to plot other data.

Operating Conditions Tab

If the data source contains data at multiple operating conditions, the Operating Conditions tab contains two columns. The Conditions column shows the available conditions, and the Values column contains a drop-down list of the available values for the corresponding condition. Use the drop-down lists to specify the operating condition values to use in simulation.

Examples

Creating a General Amplifier Block from File Data

This example uses the default data source, which is the nonlinear amplifier in the file default.s2d. The file contains S-parameters for frequencies from 1.0 to 2.9 GHz at intervals of 0.01 GHz, power data at frequency 2.1 GHz, and active noise parameters. By default, the General Amplifier block uses linear interpolation to model the network described in the object.

  1. On the Main tab, accept the default settings.

  2. On the Visualization tab, set the parameters as follows:

    • In the Plot type list, select Z Smith chart.

    • In the Y parameter1 list, select S22.

    Click Plot. This action creates Z Smith chart of the S22 parameters using the frequencies taken from the data source.

For more about using an Agilent .s2d file in a Simulink® model, see Effect of Nonlinear Amplifier on QPSK ModulationEffect of Nonlinear Amplifier on QPSK Modulation.

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