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Nonlinear Behavioral Model (Simulation-Based): NL_S

Symbol

Summary

NL_S models a Microwave Office nonlinear circuit within the Visual System SimulatorTM (VSS) program as a 2-port RF nonlinear amplifier. It uses the same underlying mechanism as the Nonlinear Behavioral Model (File-Based) block (NL_F). Instead of using a text data file, NL_S directly imports the nonlinear characterization data from the Microwave Office simulation.

The Microwave Office circuit schematic must conform to the following:

  • Have two or more PORTs

  • Have one of the PORTs configured as a one or two-tone source (two-tone recommended)

  • The source PORT should either have a power level set to the anticipated power at the input of the NL_S block or have swept power that encompasses the anticipated power.

  • Have an NLNOISE control element if noise modeling is desired.

NOTE: If your Microwave Office circuit schematic does not conform to these requirements, you should create a new schematic, add the appropriate PORT elements, and insert your original circuit as a subcircuit within the new schematic. You can also use this technique to change or restrict the frequencies at which the circuit is to be evaluated for the VSS simulations.

The characterization data obtained from the Microwave Office simulation consists of the voltage and current of the fundamental(s) at the input point, and the voltage and current of the fundamental(s) and various output harmonics and/or intermodulation products at the output point. These values are similar to those obtained using the Voltage Harmonic Component (Vcomp) and the Current Harmonic Component (Icomp) Microwave Office measurements.

In addition, the S11 seen looking into the input point when the input point is a source PORT may also be used. By default this is used for RF Budget Analysis and RF Inspector simulations, but is ignored for Time Domain simulations. The S11USERFB, S11USERFI, and S11USETD parameters can be used to change this behavior.

Note that S12 and S22 are not available from the nonlinear simulation. This is because in order to obtain S12 and S22 in a nonlinear simulation, the circuit must be driven from the output port, which is not the case.

Two-tone simulations are suggested as they provide more nonlinear characteristics for NL_S to use. They also allow the use of the Small Signal Polynomial implementation model, which can model asymmetric output fundamentals and close-in IM3 and IM5 products.

The input port of NL_S is typically set to the source PORT and the output port is set to another PORT; however, this is not a requirement. Any point within the Microwave Office circuit that may be referenced by the Vcomp or Icomp measurements can also be used for the input and output points. See the INP and OUT parameter descriptions that follow for details.

If noise modeling is desired, the Microwave Office circuit must contain a nonlinear noise control element, NLNOISE. The VSS program obtains the RMS noise voltage and conversion gain for the upper sideband and noise frequency index 0, similar to the values returned by the RMS Noise Voltage in V/sqrt(Hz) (NV) and Conversion Gain (ConvG) Microwave Office measurements with those settings. The noise voltage and conversion gain are used to compute an equivalent input referred noise current for use in the noise correlation matrices.

If you run many VSS simulations with the same Microwave Office circuit, you can avoid having to run the Microwave Office circuit simulation each time the project is loaded by saving the nonlinear characteristics of the Microwave Office circuit to a Text Data File. This feature can also be used to pass the characteristics off to others without having to send your Microwave Office circuit schematic. The NL_F_DFILE secondary parameter is used to specify the name of a text data file object to be created under the Project Browser Data Files node. Once created, the data file can be directly used by a Nonlinear Behavioral Model (File-Based) block NL_F.

If the Microwave Office circuit contains DC voltage or current sources, you can configure NL_S to output the DC source power by setting the DCPOUT parameter to "Yes". The DC source power output can be used with the Power Added Efficiency, Time Domain measurement (PAE_TD).

This block supports parameterized Microwave Office subcircuits and swept variables in the Microwave Office circuit. See Section 1.7 of the VSS Modeling Guide for details.

Parameters

Name Data Type Description Unit Type Default
ID   Element ID   S1
NET S Microwave Office subcircuit name   A
SIMTYP E Nonlinear simulator N/A Harmonic Balance
*INPORT I Id of the input PORT model in the Microwave Office circuit Scalar 1
*OUTPORT I Id of the output PORT model in the Microwave Office circuit Scalar 2
*INP S Input port/node (model.id@n) Text  
*OUT S Out port/node (model.id@n) Text  
DCPOUT E Output source DC power N/A No
NOISE E Noise modeling N/A Auto
*NOISEPORT E Port at which to generate noise N/A Auto
*TNRSEED I Thermal noise random number generator seed    
*S11USERFB E Use co-sim S11 for RF Inspector N/A Auto
*S11USERFI E Use co-sim S11 for RF Budget Analysis N/A Auto
*S11USETD E Use co-sim S11 for Time Domain N/A Auto
*BIAS R Power level bias dB 0
*IMPLTYP E Model implementation N/A Auto
*SSOPPOINT R Operating point for small signal polynomial model Scalar  
*OPPTTYP E Units for SSOPPOINT, LSLOWER and LSUPPER N/A dBm
*MAXHARM I Maximum harmonic to generate Scalar  
*LSLOWER R Lower range for large signal polynomial model data fitting Scalar  
*LSUPPER R Upper range for large signal polynomial model data fitting Scalar  
*LSDATAPTS I Minimum number of data points for large signal polynomial model data fitting Scalar  
*MDLTF E Modeled components N/A Mag & Phase
*MDLINT E Interpolation method N/A Spline
*AMCLIP E AM clipping behavior N/A 3dB+Max. Output Power
*FRQDEP E Frequency dependency behavior N/A All available frequencies
*FRQINTRP E Interpolation type for frequency dependencies N/A Linear
*FRQRES R Frequency resolution for frequency dependencies Frequency GHz
*FLTRCMP E Frequency dependency filter compensation N/A Auto
*FLTRIMP E Frequency dependency filter implementation N/A Use System Options setting
*RFIFRQ R RFI output frequency range Frequency  
*DCSUPPTYP E RFI DC suppression handling N/A Match DC from nonlinear simulation
*DCSUPP R Amount to suppress DC output in RFI simulations dB  
*SIGBW R Signal bandwidth as percentage of sampling frequency Scalar 100
*MXUPSMP I Maximum upsampling rate for anti-aliasing Scalar 1000
*SIGMODEL E Signal type for frequency dependency model N/A Auto
*DIAGDSP E Diagnostics to display N/A None
*TXTOUT E Diagnostic information to output to text window N/A None
*NL_F_DFILE S Optional name of Text Data File for NL_F Text  
*PSWP S Power sweep name Text  
*FSWP S Freq sweep name Text  
*IVARTYP   Treatment of parameters for schematic swept variables   Allow any value for numeric

* indicates a secondary parameter

Parameter Details

NET. The name of the Circuit Schematic. The name is normally enclosed in quotation marks.

SIMTYP. The type of circuit simulator to be used. If this is set to "Harmonic Balance", you can also specify a simulator not listed by appending a period followed by the simulator's tag to the name of the circuit schematic in NET. For example, if the schematic is "Amplifier" and you wish to use the AC harmonic balance simulator, you would enter "Amplifier.AC" for the parameter value.

    NET = "Amplifier.AC"

INPORT, OUTPORT. The port indices (the value of the P parameter of the PORT block, indices start from 1) of the PORT models in the Circuit Schematic to be used for the input and the output, respectively.

INP, OUT. Optional individual element nodes at which to measure the input and output power levels. These override the corresponding INPORT and OUTPORT settings.

The names have the format element.id@n, where element is the name of the element, such as TLIN, id is the value of the ID parameter of the element, and n is the node number, which starts with 1. The names are case-sensitive.

Elements within a subcircuit may also be specified by including the ID of the subcircuit containing the element followed by '\': sid\element.id@n, where sid is the ID parameter of the subcircuit.

NOISE. Determines when noise is modeled. An appropriate noise parameter must be specified in the data file in order for noise to be modeled:

  • RF Budget only: Noise is modeled for RF Budget Analysis simulations, but not Time Domain simulations.

  • RF Budget + Time Domain: Noise is modeled for both RF Budget Analysis and Time Domain simulations.

  • Noiseless: The block is assumed to be noiseless in all simulations.

  • Auto: The setting is determined from the RF Noise Modeling setting on the RF Optionstab of the System Simulator Options dialog box.

DCPOUT. Enables/disables the output of the DC source power. The DC source power is the total power generated by all the DC voltage and current sources in the Microwave Office schematic. If set to "Yes", a secondary real-signaled output port is added to the block.

The samples output are power in Watts, and can be used for the DC Power input of the Power Added Efficiency, Time Domain measurement PAE_TD.

NOTE: The DC output port is a RF port, the voltage output is the DC source power in Watts. To view the DC source power in an RF Budget Analysis simulation the Node Voltage measurement V_node should be used. For RF Inspector simulations the RFI Voltage Spectrum measurement RFI_V_SPEC should be used. For Time Domain simulations, the Waveform measurement WVFM should be used.

Because the DC output port is an RF port, if impedance mismatch modeling is enabled the port should be properly terminated such as with a LOAD block.

NOISEPORT. Determines whether the block's thermal noise is generated at the input port or at the output port in RF Budget Analysis simulations. This primarily affects the behavior of the noise generated by the block when the block is in compression. If the noise is generated at the input port it suffers the effects of compression. Selecting "Auto" currently has the same effect as selecting "Output Port".

See Chapter 3 for more on noise modeling in VSS.

TNRSEED. The seed for the time domain simulation's thermal noise pseudo-random number generator. See the Digital Random Source Block RND_D for details.

If this is left empty, a seed will be generated based on a hash of the block name and the ID parameter (if the block is within a subcircuit, the ID parameters of the parents are also used). This will in general result in different instances of the block generating different sequences, though it is not guaranteed.

If this is set to -1, the seed will vary from sweep to sweep in a single simulation run. An initial seed value similar to that generated from the block name and ID parameter is used, with a different offset added to it each new sweep. The seed sequence is deterministic between simulation runs.

S11USERFB, S11USERFI, S11USETD. Determines whether the S11 looking into the co-simulation's input point is used for a particular simulation type:

  • Use System Options Setting: The setting found under the RF Options tab of the System Simulator Options dialog boxes will be used.

  • Use S11 from Co-simulation: The S11 from the input point of the co-simulation will be used. The S11 is derived from the impedance seen looking into the input port and the characteristic impedance of the input port.

  • Ignore S11, set to 0: The S11 will be set to 0. Choosing this option is similar to inserting an ideal lossless isolator between the VSS blocks and the co-simulation input point. This is helpful when co-simulation requirements are such that a sufficiently accurate filter implementation in Time Domain simulations cannot be designed to model the frequency dependent impedance mismatch looking into the co-simulation input point.

Note that if the input point is not a port the impedance seen looking into the NL_S input port will automatically be set to the impedance looking into the input point of the co-simulation, as a characteristic impedance has not been defined and the only impedance value available is the impedance seen looking into the input point.

BIAS. Optional amount to shift the nonlinear characteristics. The BIAS value is added in dB to both the input and output power levels, including harmonics and IM products. A positive BIAS value has the effect of shifting the AM-AM curve up and to the right, effectively increasing the compression point while maintaining the gain.

IMPLTYP. Determines the model used to implement the nonlinearity:

  • Auto: The model is selected based on the characterization data provided, the frequency dependency of the data, whether or not the signal is narrowband, and whether or not the signal is fairly constant envelope.

  • Small Signal Polynomial: A 5th order polynomial model is used, with the coefficients selected to match the characterization data at a specific operating point. The operating point is determined by SSOPPOINT. This model requires at least one column of higher order data, such as IM3 or 2nd order harmonic data. This model offers broadband frequency-dependent support. It works best with input signals whose power is relatively constant around the operating point.

  • AM-AM/AM-PM: An AM-AM/AM-PM interpolation table is used, where the AM-AM and AM-PM represent the conversion of the fundamental. This model works best for narrowband frequency-independent modeling.

    NOTE: AM-AM/AM-PM requires that the signal be complex as the phase information is required. Selecting AM-AM/AM-PM when using a real signal generates an error.

  • Large Signal Polynomial (Prelim.): A 5th order polynomial model is used, with the coefficients selected to best fit the polynomial's output to the characterization data. The input power range over which the fitting is performed can be controlled with the LSLOWER and LSUPPER parameters. The number of points used for the fitting can be set with the LSDATAPTS parameter. This model offers broadband frequency-dependent support. However, because of the iterative nature of fitting algorithm, the final polynomial model might not fit the characterization data very well.

SSOPPOINT. Optional override of the operating point used for the small signal polynomial model. The units are determined by OPPTTYP. If left empty the operating point is set to the propagated signal power level at the input port.

OPPTTYP. Determines the units of SSOPPOINT, LSLOWER and LSUPPER.

MAXHARM. The maximum harmonic to generate for the polynomial models. The polynomial models are 5th order.

LSLOWER, LSUPPER. Optional lower and upper bounds of the input levels over which to fit the large signal polynomial model's coefficients to the characterization data. If left empty the bounds will be determined automatically.

LSDATAPTS. Optional number of points at which to fit the large signal polynomial model's coefficients to the characterization data. If left empty the number of points is determined automatically.

  • S21: The data file is a text data file with three columns. The first column contains the input power or voltage levels. The second and third columns define complex values that represent the S21 response for the input power level. The following is an example data file:

        InPwr(,dBm)    Gain(Mag,dB)    Phase(Phs,deg)
        -10            0               10
        0              0               10
        10             -3              30
        20             -5              45

    In this example, the first column is the input power in dBm, the second column is the S21 gain in dB and the third column is the phase distortion in degrees.

  • AM-PM: The data file is a text data file with three columns. The first column contains the input power or voltage levels. The second and third columns define complex values that represent output power or voltage and phase distortion for the input power or voltage level. The following is an example data file:

        InPwr(,dBm)    AM(Mag,dBm)    PM(Phs,deg)
        -10            -10            10
        0              0              10
        10             7              30
        20             15             45

    In this example, the first column is the input power in dBm, the second column is the output power in dBm and the third column is the phase distortion in degrees. This example has characteristics equivalent to the S21 example.

NOTE: The type and units of the column headings in the first line are used to define the units and the complex value component represented by the second and third columns. However, the tags are ignored (InPwr, Phase, AM and PM are not valid tags).

MDLTF. Selects the characteristics to be modeled for the AM-AM/AM-PM model:

  • Mag & Phase: Both amplitude and phase distortion are applied.

  • Mag only: Only amplitude distortion is applied, the signal phase is unchanged.

  • Phase only: Only phase distortion is applied, the magnitude is unchanged.

MDLINT. Selects the interpolation to use between the input power levels characteristics for the AM-AM/AM-PM model:

  • Cubic Spline: Cubic spline interpolation results in smooth power (in dB) and phase distortion curves between input power levels from the data file.

    NOTE: The curve may contain wide amplitude variations between data points if the input power levels are unevenly spaced.

  • Linear: Linear interpolation results in linear power (in dB) and phase distortion curves between the input power levels from the data file. The curves typically have discontinuous slopes at the specified input power levels.

The following diagram illustrates the differences between the different MDLINT options. The AM-AM/AM-PM curve used was (with DFTYP="S21"):

    InPwr(,dBm)    (Mag,dB)    (Phs,deg)
    -10            5           10
    -5             8           10
    0              0           20
    5              6           30
    10             3           40

The data points are spaced at 1 dB intervals along the x-axis. The curve with triangle markers illustrates "Cubic Spline". The curve with box markers illustrates "Linear".

AMCLIP. Determines the amplitude distortion when the instantaneous input power level exceeds the maximum specified input power level for the AM-AM/AM-PM model:

  • 3dB+Max. Output Power: The output power level is clipped to 3dB above the output power level at the maximum specified input power level IF the power curve has a positive slope at the maximum specified input power level. If the slope is 0 or negative, the output power level is set to the output power level at the maximum specified input power level, the same as the "Max. Output Power" option.

  • Max. Output Power: The output power is clipped to the output power level at the maximum specified input power level. A warning message displays when the output power level is first clipped.

  • Linear Extrapolation: The output power level is linearly extrapolated using the slope of the power curve at the maximum specified input power level.

The phase distortion is linearly extrapolated from the phase distortion at the maximum specified input power level.

The following diagram illustrates the different AMCLIP options. The AM-AM/AM-PM curve used was (with DFTYP="AM-PM"):

    InPwr(,dBm)    AM(Mag,dBm)    PM(Phs,deg)
    -10            -5             10
    -5             0              10
    0              5              20
    5              10             30
    10             13             45

with cubic spline interpolation. The maximum input power level is 10 dBm with an output power level of 13 dBm.

The top curve (with diamond markers) illustrates "Linear Extrapolation". The curve is a straight line, continuing the slope from the last point.

The middle curve (with triangle markers) illustrates "3dB + Max. Output Power". The curve smoothly continues from last point until it reaches 16 dBm (13+3dBm).

The bottom curve (with X markers) illustrates "Max. Output Power". The power level is simply clipped to 13 dBm.

FRQDEP. Determines how frequency-dependent data is handled:

  • Frequency independent: A frequency-independent nonlinearity is modeled. The data set whose frequency is closest to the center frequency is used.

  • All available frequencies: Frequency dependency is modeled using all the data sets whose frequencies fall within the sampling frequency band.

  • Data set closest to center frequency: The data set whose frequency is closest to the center frequency is used. If the data set is a frequency-dependent two-tone data set, the frequency dependency is modeled. This option is useful when you have two-tone data sets at several frequencies. Restricting the model to only one data set prevents the other data sets from inadvertently influencing the model.

  • Auto: If the data set contains frequency dependent IM product information, then 'All available frequencies' will be chosen for non-Time Domain simulations, or if more that one frequency data set falls within the sampling frequency band. Otherwise, the behavior is similar to 'Data set closest to center frequency'.

FRQINTRP. Determines how values for frequencies between the frequencies in the data set are interpolated.

FRQRES. Determines the frequency resolution of the filters used to implement the frequency dependencies. The number of taps in the filters is the sampling frequency divided by the frequency resolution. If left empty FRQRES is determined automatically. For speed performance reasons FRQRES is limited to the sampling frequency/100000.

FLTRCMP. Determines how delay introduced by any frequency dependency filters is compensated for.

  • Auto: This is currently the same as 'Compensate filter phase delay'.

  • Compensate filter phase delay: Delay introduced by the filters is removed from the signal when the block is not in a feedback loop.

  • Ignore filter phase delay: Delay introduced by the filter is included in the signal.

FLTRIMPL. Determines the type of implementation used by the frequency dependency filters.

  • Use System Options setting: The option selected in the System Simulator Options dialog box under the RF Options tab is used. The options are the same as the ones below.

  • IIR modulated with phase, FIR otherwise: If the input signal is from a modulated signal source and the frequency dependency has non-constant phase, an IIR filter implementation will be used, otherwise an FIR filter implementation will be used.

  • FIR: An FIR filter implementation will be used.

  • IIR: An IIR filter implementation will be used.

IIR filters tend to provide a frequency response closer to the desired frequency response compared to FIR filters when portions of a signal fall between the FIR filter bin frequencies. This occurs when the signal is not a CW signal, or the CW signal frequency does not fall on an FIR bin frequency. However, the downside of the IIR filters is that a reasonable approximation of the desired frequency response is not always possible.

The spectrum of the signal should be observed before and after the filter if the filter has frequency dependency, and if the output spectrum does not appear correct, try setting FLTRIMPL to FIR to force an FIR filter implementation.

RFIFRQ. Optional frequency range for restricting RFI output signals. If this is a two element vector, the two elements specify the lower and upper limits of the RFI frequencies to generate. If this is a single value, the value is the bandwidth about the center frequency. The frequency range specified overrides any RFI frequency range limits specified in the Simulation Options dialog boxes.

DCSUPPTYP. Determines how DC suppression in RF Inspector simulations is handled:

  • Match DC from nonlinear simulation: The DC suppression is automatically computed, and is set so the DC output matches the circuit simulation's DC when the input power levels and port loads match those of the circuit simulation.

  • Use DCSUPP: The value of the DCSUPP parameter is used.

DCSUPP. Amount to suppress the DC output of the block in RF Inspector simulations. Positive values decrease the DC output, and negative values increase the DC output. Setting DCSUPP to 400 or greater results in no DC output being generated. Leave this option empty to have DC suppression determined by the Amplifiers do not pass DC by default setting on the System Simulator Options dialog box RFI/RFB Settings tab.

SIGBW. Percentage of the sampling frequency bandwidth occupied by the signal of interest. The anti-aliasing mechanism uses the signal bandwidth to determine the amount of resampling needed, if any, to avoid aliasing.

This may be left empty. If so, the block attempts to determine the bandwidth based on the samples per symbol used to generate the input signal.

MXUPSMP. The maximum upsample rate allowed for the anti-aliasing resampler. If the simulation runs extremely slow try reducing this value at the potential expense of decreasing accuracy due to aliasing.

DIAGDSP. Enables the display of diagnostic information such as the coefficients and saturation settings used for the polynomial models. The information displays in the Text Output window.

TXTOUT. Enables the display of S21 or AM-AM/AM-PM tables in the Text Output window when DIAGDSP is set to "Full".

NL_F_DFILE. The optional name of a Text Data File to create that contains the Microwave Office circuit's nonlinear characteristics in a format supported by the Nonlinear Behavioral Model (File-Based) block (NL_F). The data file is created as a data file object under the Data Files node of the Project Browser. If there is an existing data file with the same name, the contents of the data file are replaced. Note that the data file will include the S11 information from the co-simulation only if S11USERFB, S11USERFB, or S11USETD is appropriately set for the current simulation.

PSWP. The optional name of the power sweep to use. If left empty, the default power sweep for the Microwave Office circuit is used.

FSWP. The optional name of the frequency sweep to use. If left empty, the default frequency sweep is used. If '.$FPRJ' is added to the end of the circuit schematic name in the NET parameter the default frequency sweep is the project frequencies and is FSWP is set to FPRJ. Otherwise, the default frequency sweep is the document frequency sweep and FSWP is set to FDOC.

IVARTYP. Determines the behavior of the dynamic parameters representing the swept variables of the Microwave Office schematic.

  • Allow any value for numeric, pin to nearest: The parameters allow any numeric value, and the data set with the swept variable closest to the parameter value is used.

  • Select from list: The parameters display a list of available values for the swept variables.

Data Input

Node No. Type Purpose
1 Complex, Real Input Signal

Data Output

Node No. Type Purpose
2 Complex, Real Output Signal
3 Real DC Source Power in Watts (only present if DCPOUT is "Yes")

Implementation Details

NL_S utilizes the same underlying implementation as NL_F. See the NL_F documentation for details on the underlying implementation.

NL_S obtains the nonlinear characterization data from the Microwave Office simulation. If the Microwave Office simulation is a one-tone simulation, the voltage and current of the fundamental at the input PORT or element node are used for the input signal. The voltages and currents of the fundamental and 2nd through 5th order harmonics at the output PORT or element node are used for the output signal characteristics.

If the Microwave Office simulation is a two-tone simulation, the voltages and currents of the two fundamentals at the input PORT or element node are used for the input signal. The voltages and currents of the two fundamentals, the two 2nd order harmonics, and the (-1,2), (2,-1), (-1,3), (3,-1), (-2,3), and (3,-2) IM products at the output PORT or element are used for the output signal characteristics. These voltages all represent the total voltage seen at the PORT or element node.

How these voltages and currents are used depends on whether the input is a PORT element or an element node. If the input is a PORT element, the input voltages are first converted to incident voltage before being used to generate the appropriate model. If the input is an element node, the total voltages at the input are used for generating the implementation model. For the AM-AM/AM-PM model, the transfer function is treated as a voltage transfer function and no conversion to power is made.

Impedance Mismatch Modeling

The characteristic impedances and reflection coefficients seen at the input and output ports of the NL_F block depend on whether the input/output is a PORT element or an element node.

If the input/output is a PORT element, the characteristic impedance of the input/output port of the NL_S block is set to the characteristic impedance of the PORT element. S11/S22 is set using the characteristic impedance of the PORT and the impedance computed from the total voltage and the current at the PORT if the corresponding S11USERFB, S11USERFI, or S11USETD is set to use the S11 values.

If the input/output is an element node, the characteristic impedance of the input/output port of the NL_S block is set to the impedance computed from the total voltage and current at the element node. The current direction is reversed as necessary to ensure the real component of the impedance is non-negative.

The impedances seen looking out the ports of the NL_S block are NOT applied to the Microwave Office circuit simulation. The Microwave Office simulation uses the impedances specified in the PORT elements of the circuit schematic. Care must be taken to apply the proper impedances if the Microwave Office circuit's transfer function is highly dependent upon the source or load impedances.

The following diagram illustrates how the Microwave Office circuit fits into the VSS simulation when the input and output of the NL_S block are set to PORT elements. The Microwave Office circuit is treated as if it has ideal isolators at its input and output. To the VSS simulation, the block's nodes appear as terminations with the impedances from the corresponding Microwave Office circuit diagram's ports.

ZInp is the port impedance of the input port in the Microwave Office circuit, ZOut is the port impedance of the output port.

If there is an impedance mismatch present on the input node, the following correction is applied to convert the signal from total voltage to incident voltage:

If there is an impedance mismatch present on the output node, the following correction is applied to convert from reflected voltage to total voltage:

NOTE: S12 modeling is restricted to RF Budget Analysis and RF Inspector simulations. It also requires that the impedances at the input port match. If the impedances are not matched, the total voltage and current at the input port may be incorrect due to the requirement that nonlinear blocks synthesize S12 voltage in the RF Budget Analysis and RF Inspector simulations.

See Chapter 2 for more on impedance mismatch modeling in VSS software.

Noise Modeling

When noise generation is enabled, NL_S obtains a noise factor from the Microwave Office nonlinear noise simulation. This requires that the Microwave Office Circuit Schematic have an NLNOISE control element properly configured.

NL_S uses the frequency index 0 upper sideband RMS noise voltage and available gain for its computation. The RMS noise voltage is the same value returned by the Microwave Office NV measurement and the available gain is the same value returned by the Microwave Office ConvG measurement.

Frequency index 0 corresponds to the NLNOISE element NFstart parameter. This should be a fairly small value (say ≤ 0.1% of the center frequency), as NL_S ignores the offset and applies the value at the frequency being swept.

At each frequency of the Microwave Office simulation NL_S computes an equivalent input referred noise current from the RMS noise voltage and available gain.

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