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Amplifier

Model amplifier in RF systems

• Library:
• SimRF / Circuit Envelope / Elements

Description

Use the Amplifier block to model a linear or nonlinear amplifier, with or without noise. Defining the amplifier gain using a data source also defines input data visualization and modeling. Use the Main tab parameters to specify amplifier gain and noise using data sheet values, standard `s2p` files, S-parameters, or circuit envelope polynomial coefficients.

The amplifier is implemented as a polynomial, voltage-controlled voltage source (VCVS). The VCVS includes nonlinearities that are described using parameters listed in the Nonlinearity tab. To model linear amplification, the amplifier implements the relation Vout = a1*Vin between the input and output voltages. The input voltage is Vi(t) = Ai(t)ejωt, and the output voltage is Vo(t) = Ao(t)ejωt at each carrier w = 2πf in the SimRF™ environment.

Nonlinear amplification is modeled as a polynomial (with the saturation power computed automatically). It also produces additional intermodulation frequencies.

Parameters

expand all

Main

Source parameter of the amplifier gain, specified as one of the following:

• `Available power gain`Available power gain parameter is used to calculate the linear voltage gain term of the polynomial VCVS, a1. This calculation assumes a matched load termination for the amplifier.

• `Open circuit voltage gain`Open circuit voltage gain parameter is used as the linear voltage gain term of the polynomial VCVS, a1.

• `Data source` — Linear voltage gain term of the polynomial VCVS is calculated from the specified data source options:

for the maximal value of S21.

When using the data source option, S11 and S22, are used as the input and output impedances. The data sources are specified using either `Data file` or `Network-parameters` or ```Rational model```, depending on the value of `Data source`.

• `Polynomial coefficients` — The block implements a nonlinear voltage gain according to the specified polynomial coefficients

Available power gain of amplifier, specified as a scalar in dB. Specify the units from the corresponding drop-down list.

Dependencies

To enable this parameter, choose ```Available power gain``` in the Source of amplifier gain tab.

Open circuit voltage of amplifier, specified as a scalar in dB. Specify the units from the corresponding drop-down list.

Dependencies

To enable this parameter, choose ```Open circuit voltage gain``` in the Source of amplifier gain tab.

Data source, specified as one of the following:

• `Data file` — Name of a Touchstone file with the extension`.s2p`. The block ignores noise and nonlinearity data in imported files.

• `Network-parameters` — Provide Network parameter data such as `S-parameters`, `Y-parameters`, and `Z-parameters` with corresponding Frequency and Reference impedance (ohms) for the amplifier.

• `Rational model` — Provide values for Residues, Poles, and Direct feedthrough parameters which correspond to the equation for a rational model

`$F\left(s\right)=\left(\sum _{k=1}^{n}\frac{{C}_{k}}{s-{A}_{k}}+D\right)\begin{array}{cc},& s=j2\pi f\end{array}$`

.In this rational model equation, each Ck is the residue of the pole Ak. If Ck is complex, a corresponding complex conjugate pole and residue must also be enumerated.This object has the properties `C`, `A`, and `D`. You can use these properties to specify the Residues, Poles, and Direct feedthrough parameters.

Dependencies

To enable this parameter, select `Data source` in Source of amplifier gain tab.

Order of polynomial, specified as a vector.

The order of the polynomial must be less than or equal to 9. The coefficients are ordered in ascending powers. If a vector has 10 coefficients, ```[a0,a1,a2, ... a9]```, the polynomial it represents is:

Vout = a0 + a1Vin + a2Vin2 + ...  + a9Vin9

where a1 represents the linear gain term, and higher-order terms are modeled according to [1].

For example, the vector `[a0,a1,a2,a3]` specifies the relation Vo = a0 + a1V1 + a2V12 + a3V13. Trailing zeroes are omitted. If a3 = 0, then `[a0,a1,a2]` defines the same polynomial as ```[a0,a1,a2, 0]```. The default value of this parameter is [0,1], corresponding to the linear relation Vo = Vi.

Dependencies

To enable this parameter, select `Polynomial coefficients` in Source of amplifier gain tab.

Network parameter type, specified as `S-parameters`, `Y-parameters`, or `Z-parameters`.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select `Network-parameters` in the Data source tab.

Input impedance of amplifier, specified as a scalar.

Dependencies

To enable this parameter, select ```Available power gain```, `Open circuit voltage gain`, or `Polynomial coefficients` in Source of amplifier gain tab.

Output impedance of amplifier, specified as a scalar.

Dependencies

To enable this parameter, select ```Available power gain```, `Open circuit voltage gain`, or `Polynomial coefficients` in Source of amplifier gain tab.

Name of network parameter data file, specified as a character vector.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select `Data file` in Data source.

Noise figure of amplifier, specified as a scalar in dB. The default value of this parameter is `0` dB, which implies that no noise is added to the system by this block.

You can model noise in a SimRF model with a Noise, Resistor, Amplifier, or Mixer block. To do so, in the Configuration block dialog box, verify that the Simulate noise check box is selected (default).

If the noise figure is a part of the file specified in the ```Data source```, then the following message is displayed ```Noise specified in Data file```.

Frequency of network parameters, specified as a scalar in Hz.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select `Network-parameters` in Data source.

Reference impedance of network parameters, specified as a scalar.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select `Network-parameters` in Data source.

Residues in order of rational model, specified as a vector.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select ```Rational model``` in Data source.

Poles in order of rational model, specified as a vector.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select ```Rational model``` in Data source.

Direct feedthrough, specified as an array vector.

Dependencies

To enable this parameter, first select `Data source` in Source of amplifier gain tab. Then, select ```Rational model``` in Data source.

Polynomial coefficients, specified as a vector.

Dependencies

To enable this parameter, select `Polynomial coefficients` in Source of amplifier gain tab.

Select this option to ground and hide the negative terminals. Clear this parameter to expose the negative terminals. By exposing these terminals, you can connect them to other parts of your model.

By default, this option is selected.

Nonlinearity

Type of nonlinearity, specified as ```Even and odd order``` or `Odd order`.

• When you select `Even and odd order`, the amplifier can produce second- and third-order intermodulation frequencies in addition to a linear term.

• When you select `Odd order`, the amplifier generates only odd order intermodulation frequencies.

The linear gain determines the linear a1 term. The block calculates the remaining terms from the specified parameters. These parameters are IP3, 1-dB gain compression power, Output saturation power, and Gain compression at saturation. The number of constraints you specify determines the order of the model. The figure shows the graphical definition of the nonlinear amplifier parameters.

Intercept points convention, specified a `Input`-referred, or `Output`-referred convention. Use this specification for the intercept points, 1-dB gain compression power, and saturation power.

Second-order intercept point, specified as a scalar.

Dependencies

To set this parameter, select `Even and odd order` in Nonlinear polynomial type.

Third-order intercept point, specified as a scalar.

1-dB gain compression power, specified as a scalar.

Dependencies

To set this parameter, select `Odd order` in Nonlinear polynomial type.

Output saturation power, specified as scalar. The block uses this value to calculate the voltage saturation point used in the nonlinear model. In this case, the first derivative of the polynomial is zero, and the second derivative is negative.

Dependencies

To set this parameter, select `Odd order` in Nonlinear polynomial type.

Gain compression at saturation, specified as scalar.

When Nonlinear polynomial type is ```Odd order```, specify the gain compression at saturation.

Dependencies

To set this parameter, first select `Odd order` in Nonlinear polynomial type. Then, change the default value of Output saturation power

Modeling

Model S-parameters, specified as:

• Time-domain (rationalfit) technique creates an analytical rational model that approximates the whole range of the data. When modeling using `Time domain`, the Plot in `Visualization` tab plots the data defined in `Data Source` and the values in the `rationalfit` function.

• Frequency-domain computes the baseband impulse response for each carrier frequency independently. This technique is based on convolution. There is an option to specify the duration of the impulse response. For more information, see Compare Time and Frequency Domain Simulation Options for S-parameters.

• For the Amplifier and S-parameters blocks, the default value is `Time domain (rationalfit)`. For the Transmission Line block, the default value is `Frequency domain`.

Dependencies

To set this parameter, first select `Data source` in Source of amplifier gain. This selection activates the Modeling Tab which contains Modeling options

Rationalfit fitting options, specified as `Fit individually`, ```Share poles by column```, or `Share all poles`.

Rational fitting results shows values of Number of independent fits, Number of required poles, and Relative error achieved (dB).

Dependencies

To set this parameter, select `Time domain (rationalfit)` in Modeling options.

Relative error acceptable for the rational fit, specified as a scalar.

Dependencies

To set this parameter, select `Time domain (rationalfit)` in Modeling options.

Select this parameter to automatically calculate impulse response. Clear this parameter to manually specify the impulse response duration using Impulse response duration.

Dependencies

To set this parameter, select `Frequency domain` in Modeling options.

Impulse response duration, specified as a scalar.

Dependencies

To set this parameter, first select `Frequency domain` in Modeling options. Then, clear ```Automatically estimate impulse response duration```.

Visualization

Frequency data source, specified as:

When Source of frequency data is ```Extracted from data source```, the Data source must be set to `Data file`. Verify that the specified Data file contains frequency data.

When Source of frequency data is `User-specified`, specify a vector of frequencies in the Frequency data parameter. Also, specify units from the corresponding drop-down list.

Dependencies

To set this parameter, first select `Data source` in Source of amplifier gain. This selection activates the Visualization Tab which contains Source of frequency data

Frequency data range, specified as a vector

Type of data plot that you want to produce with your data specified as one of the following:

• `X-Y plane` — Generate a Cartesian plot of your data versus frequency. To create linear, semilog, or log-log plots, set the Y-axis scale and X-axis scale accordingly.

• `Polar plane` — Generate a polar plot of your data. The block plots only the range of data corresponding to the specified frequencies.

• `Z smith chart`, ```Y smith chart```, and `ZY smith chart` — Generate a Smith® chart. The block plots only the range of data corresponding to the specified frequencies.

Type of S-Parameters to plot, specified as `S11`, `S12`, `S21`, or `S22`.

Type of S-Parameters to plot, specified as `S11`, `S12`, `S21`, or `S22`.

Plot format, specified as `Magnitude (decibels)`, `Angle(degrees)`, `Real`, or `Imaginary`.

Plot format, specified as `Magnitude (decibels)`, `Angle(degrees)`, `Real`, or `Imaginary`.

Y-axis scale, specified as `Linear` or `Logarithmic`.

X-axis scale, specified as `Linear` or `Logarithmic`.

Plot specified data using plot button.

References

[1] Gonzalez, Guillermo. "Microwave Transistor Amplifiers: Analysis and Design", Englewood Cliffs, N.J.: Prentice-Hall, 1984.

[2] Grob, Siegfried and Juergen Lindner. "Polynomial Model Derivation of Nonlinear Amplifiers, Department of Information Technology, University of Ulm, Germany.

[3] Kundert, Ken. "Accurate and Rapid Measurement of IP 2 and IP 3", The Designers Guide Community, Version 1b, May 22, 2002. http://www.designers-guide.org/analysis/intercept-point.pdf.

[4] Pozar, David M. "Microwave Engineering", Hoboken NJ: John Wiley & Sons, 2005.